This descriptive catalogue of the collection of microscopes in charge
of the Utrecht University Museum differs in a few respects from
most, if not all, catalogues of other collections- It is, in the first place,
not concerned only with the design and the mechanical arrangement
of the instruments, as is usually the case, but it also aims at giving,
with constant reference to the Utrecht collection, a survey of the his-
torical development of the magnification and the resolving powers
as well. In the second place, it deals with the 19th century microscopes
in more detail than is to be found in the greater number of such
catalogues. The development during that period is, indeed, by no
means less important and interesting than during the 18th century.
In the 19th century, too, one meets with tentative efforts to arrive at
the best form for the supporting stand and also with a variety of minor
alterations, introduced as improvements, but subsequently withdrawn.
Above all, however, the 19th century is remarkable for the develop-
ment of the simple non-corrected objective into the modern one whose
actual resolving power has practically reached its theoretical value.

This collection contains a few unique instruments of great historical
interest. To begin with, there is the strongest of the remaining quot;van
Leeuwenhoekquot; microscopes, further, the achromatic objective of
Beeldsnijder made about 1791 and, finally, the two different types of
the first achromatic microscope ever introduced on the market, both
of them constructed by van Deijl about 1806. It contains, as well, the
greater part of those instruments of which Harting published, in his
well-known standard work, the magnifying and resolving powers as
determined by him. For a long time Harting was a professor at Utrecht
and director of the Zoological Laboratory, and not only the instru-
ments belonging to that institute were at his disposal but also those
belonging to the Physical Laboratory, which then, already, had be-
come an important collection.

The Utrecht microscope collection itself is only a part of a very
extensive collection of instruments (about 1200) owned by the
University and in which three smaller collections arc combined. First
of all, namely, the instruments purchased since the year of its foun-
dation (1706) by the Theatrum Physicum, secondly, those collected

by the Physical Society (Natuurkundig Gezelschap) and thirdly, those
brought together by the Utrecht University Museum. As regards the
share of the Natuurkundig Gezelschap (which was founded in 1777
and still flourishes) we may remark that, especially during the first
hundred years of its existence, it could dispose of ample means and
started an exceedingly valuable collection of instruments which it
ceded on certain conditions to the University in 1889. As regards
the third contributor, the Utrecht University Museum, this includes*
among its activities the extension of the present collection. It is res-
ponsible for the description of the collection and also for the publi-
cation of this catalogue for which it gratefully acknowledges the
financial support of the Utrecht University Fund.

Ergötzung. I 1763, II 1761.
H. Baker. Het Mikroskoop gemakkelijk gemaakt, enz. 1778.

and development of the Microscope. 1928 (Catalogues of the Royal
Microscopical Society).
R. S. Clay and Th. H. Court. The History of the Micros-
cope. 1932.

The discovery of the lens includes the discovery of the microscope,
for, once the first positive lens was constructed, its magnifying
power must at once have been apparent. This means that the first
microscope had thereby come into existence though most probably its
magnification and resolving power were very poor. In course of time,
however, it must have become obvious that the magnifying power of
lenses increases with increasing curvature of their surfaces. Hence
the tendency must have arisen to obtain ever stronger lenses by making
them continually smaller. Since, however, the manipulation of such
minute lenses became more and more inconvenient, it was only natural
to mount them in some kind of lens-holder or supporting stem and to
fit such a lens-holder or stem with an object-holder provided with a
contrivance for the control of the focussing. This is how, what is
commonly called, the simple microscope came into being, a type of
instrument which held its own as long as until about 1830. And
rightly so, for, however difficult the instrument may have been to
handle, especially on account of the very small object distance
necessary with higher magnifications, its optical quahties were unsur-
passed then by any other type of instrument. The images are remark-
ably free from spherical and chromatic aberration, even with a magni-
fication of 500 they give an impression of still being, practically
speaking, perfectly achromatic. Indeed, as is clear from theoretical
considerations, all aberrations from the ideal image, excepting the
deviation from flatness, will in the case of strongly curved nearly
spherical lenses only sligtly deteriorate the quality of the image.

From its origin down to the middle of the 19th. century the simple
microscope has developed from a very primitive into a refined physical
instrument. Whereas the earliest microscope consisted simply of a
short tube fitted with a lens at one end and having the object attached
(o it at the other, the microscope constructed shortly after 1800 had a
beautifully made supporting pillar, a convenient stage which often
admitted of central adjustment and a perfect contrivance for focussing.

Though the closer study of the mechanical and constructional
development of the microscope is very interesting, it is no doubt
equally interesting to follow the development of the magnifying and
resolving powers of these instruments during that same period And
the remarkable result is that from the earliest microscope in the Utrecht
collection (and of the 17th century too), down to the middle of the
19th century hardly any improvement is found. The van Leeuwenhoek
instrument, described under A. 1. proves to be one of the best micros-
copes as regards magnification and resolving powers made until the
commencement of the 19th century. In order to make sure of this fact,
all microscopes of the collection here described have been brought
once more into a workable condition, all lenses have been cleaned
as thoroughly as possible, and after these preliminaries the magnifi-
cation and the resolving power of all instruments have been deter-

quot;quot; Fot the stronger simple microscopes as well as for the projection-
microscopes the determination of the magnification was carried out
by throwing the image of a reading scale, formed by the lens under
investigation, on to a screen, at a fixed distance from the lens, and
by measuring the length of the divisions. For the weaker simple
microscopes and for the compound ones it was done with the aid
of the camera lucida. All magnifications, those of the projection
microscopes inclusive, are given for 25cm image distance.

As regards the determination of the resolving power, it was not
possible to make use of the aperto-meter. as is usually done nowadays,
because the numerical aperture gives the resolving power for those
cases only in which both lenses and conditions for illumination are
ideal As soon as the lenses and the illumination are not ideal, the
result of the aperto-meter method can only have the signification of
an upper limit and the true resolving power corresponding to the
actual state of affairs remains unknown. Even with the modern in-
struments of the best manufacture there is no absolute guarantee that
the actual conditions agree sufficiently closely with the ideal ones to
permit the application of the aperto-meter method.

When dealing, however, with instruments of the 17th and 15th
centuries one may be sure that the actual conditions fall so far short
of the ideal ones that this method can no longer be applied. It had
therefore to be replaced by a direct one, now almost forgotten but
in common use about the middle of the 19th century. This direct
method gives at once the true resolving power for the actual condition
cf the lenses and illumination during the measurements and ought
therefore strictly speaking, to be preferred even for modern instru-
ments to the first one. In the middle of the 19th century this method
made use of a so-called Nobert's test plate, that is. a small glass plate
in which a few groups of parallel equidistant lines are scratched, the

mutual distances for each group being known, (cp. W. 5). Later on
the quot;Grayson Rulingsquot; i) became more popular as a testing object.
This is a thin realgar-film, also with a number of groups of
parallel equidistant lines scratched on it (cp. W. 6). For the present
determinations both the Nobert plate and the Grayson Rulings were
used, mainly the latter, however, which in our case contained 12 groups
of lines.

Numbering the groups in the order of their decreasing mutual line-
distances, the latter amounts tor group a to 1/5000 a inch, which is
equal to about V200a mm. If now, the examination of the plate in
the microscope shows that group a is still resolved but the next group
a / not yet, the resolving power is sure to have a value between

For the small magnifications an object micrometer was used with
divisions in 1/100 mm. Our numerical results for the resolving powers

source of light for this investigation was, except in the case of very
high magnifications, an electric lamp at a distance of about one meter:
the measurements are, therefore, the results of experiments with
lightpencils of very slight divergence.

Let us now return to the simple microscope- It was clear from the
measurements, that for the microscopes described below, one could
fix, fairly sharply, the average magnification required to reach some
definite resolving power. For instance, lenses with magnifications
smaller than X 20 turned out not to be capable of resolving V100 mm.
For resolving powers between Vioo mm. and Vuoo mm, the required
magnifications had as a rule values between 20 and 40, etc. The results
are collected in Table 1, and in fig. 1 the resolving power of the
simple microscope is plotted against the magnification (continuous

^'^Here, we are struck by the fact that the point L furnished by the
oldest instrument of the collection, (the van Leeuwenhoek microscope)
not only fits the curve perfectly, (a magnification of 270 resolves in
this case 1/700 mm. i.e. the 4th group of a Nobert plate) but that it
even lies very high on the curve; it is only surpassed by a few 19th
century microscopes fitted with doublets and by one, only one, small
lens of Dollond dating from that same period, with a magnification
of 480.

Considering that van Leeuwenhoek's instrument attains its pro-
minent position in spite of a badly scratched lens it would in its

1) These were introduced on the market by the firm Bcck in London; they are
nowadays, however, no longer made and have, practically speaking, disappeared
from the market.

As regards the projection-microscopes, one might, from theory,
expect the same relation between magnification and resolving power
as that of the simple microscopes, for the fact that one uses the lens
(of short focal length) in the first case as a projecting lens instead of as
a magnifying glass does not appreciably alter the object distance, and,
therefore, neither the numerical aperture. In reality, however, the
resolving power proved to be less than that of the simple microscopes;

the obvious reason herefore is that the screen is never perfectly flat.
The more it approaches ideal flatness the closer the resolving power
will be to that of the simple microscope. In agreement herewith it was
found experimentally that the resolving power is greater for projec-
tion distances of more than 25 cm. In order, however, to make a fair
comparison with the simple microscope possible, the screen was held
at the fixed distance of 25 cm from the lens. K sheet of white card-
board as smooth and as flat as possible, was used as a projection
screen. The results are again given in Table 1.

We will now consider the development of the compound micros-
cope as well. To all appearances, its more convenient manipulation

and the greater object distances, offered the observer many advan-
tages- Here again, however, one meets with the same phenomenon
as in the other types of microscopes. In the course of the 18th century
namely, a considerable improvement in the mechanical construction
was obtained, but hardly any progress was made as regards the
optical capacities, and moreover, the optical powers of the compound
microscopes turned out to fall short, by a long way, of those of the
simple microscopes. This can be seen at once in Table 1 and from
the dotted curve of fig. 1. A comparison, too, in the present catalogue
of the optical data of the various instruments will at once reveal the
fact that optical capacities of the compound microscopes have remai-
ned the same during the whole of the 18th century. The original
Culpeper microscope, for instance, shows in this respect, hardly any
difference from those instruments constructed about 1800. Even those
improvements which were obviously necessary were neglected; the
objectives, for example, are found to consist in the majority of cases
of bi-convex lenses, if one comes across plano-convex lenses at all,
they are almost invariably mounted with their convex surfaces turned
towards the object and have evidently only been put in for the sake
of their convenient mounting.

The reason why the magnifications of the compound microscopes
are less than those of the other types is that the influence of the
chromatic and spherical aberrations is much more predominant. 1 he
resolving power is less for the obvious reason, that a single
lens used as a simple microscope has a definite resolving power which
can never increase, though its magnification can increase when the
lens is subsequently combined with an eyepiece. If often occurs on
the contrary that the resolving power of the combination is less than
that of the single lens so that higher magnifications and lower
resolving powers belong together.

Whereas the resolving power of the compound microscope remain-
ed therefore, far below that of the simple microscope, so long as
the objectives were not achromatized, this was no longer the case
when once achromatic objectives were successfully made. The very
first achromatic objective of Beeldsnijder (1791) is capable, when
combined with a low power eye-piece, of resolving i/,oo mm with a
magnification of 20 (fig. 1 point B). With van Deyl's microscope
(1806 M. 2) Vquot;oo mm's already resolved with a magnification of 30
(fig. 1 point D). This proves that though as yet restricted to low
magnifications only, the construction of the achromatic objective
brought the compound microscope at once up to the level, or even
above the level, of the simple microscope. It is worthy of note that
in our opinion van Deyl owes his remarkable success not only to
his achromatic objective, but also to the fact that he constructed his
lenses in such a way that they partly neutralized their separate sphe-
rical aberrations. Both surfaces of all the lenses in his instrument
have different curvatures and are mounted in such a way that the
light-pencils that go to form the image pass through them at favorable

Soon however, the restriction to low magnification was felt as a
serious drawback. The achromatic objective must necessarily consist
of a convex crown lens and a concave flint lens. Now in order to
obtain high magnifications the convex lens must be very much more
powerful than in the case of a single nonachromatized lens and this
leads to practical difficulties in their construction. Selligue and Che-
valier, soon followed by others, were the first to obtain high magni-
fications by combining into a system a number of small lenses each
of which had been achromatized separately as well as possible- 1 he
advantage of this method was that by simply adding or removing one
or more of the lenses one could very easily alter the magnification.
The drawback, however, was the accumulation of the separate sphe-
rical aberrations, which in the case of higher magnifications spoiled
the resolving power. This explains why the resolving power of the
compound microscope, though increased considerably by achromatiz-

ing. still remained below that of the simple microscope. This is clearly
demonstrated by the instrument (O. 1) constructed in 1837 by Cheva-
lier, one of the best builders of microscopes of his time. From Table 1

It is due to the genius of Amid that these difficulties were over-
come. He showed that, in order to arrive at a high resolving power,
the objective must be composed of different parts each of which
separately still gives rise to aberrations, but which are so computed,
that they neutralize each others impairing influence. He was also the
first to draw attention to the part played by the cover-glass and to
point out the great advantage of having at one's disposal a number
of eyepieces of different powers, as well as a number of different
objectives. He pointed out. moreover, the influence of a larger aper-
ture and the important advantage of immersion. The microscope
of Amid (1836) in the Utrecht collection turns out indeed to
possess a resolving power far exceeding that of the simple micros-
cope; with a magnification of 80 it resolves already 1/400 mm (fig. 1
point A). When his method of constructing objectives was once gener-
ally accepted and followed, and the resolving power of the com-
pound microscope went up by leaps and bounds, the cause of the
simple microscope was lost! The microscope of Oberhäuser (about
1845. see Q. 2) or better still that of Hartnack (about 1870, see Q. 3)
makes this clear to us in a most convincing way. (See Table 1 and

to the Hartnack microscope moreover shows, that, in the case of lower
magnifications, this instrument has already reached the theoretical
limit represented in fig. 1 by two continuous straight lines. The
horizontal line gives the theoretical limit for NA = 0.9 and A =
5000 A The construction of the slanting line is based on the experi-
mental fact that the angular distance of two points must be at least
IH' in order to be seen separately. And the achievement of a water-
immersion. belonging to the same Hartnack instrument and which,
with a magnification of 340 is able to resolve V,soo mm is also
represented in fig. 1 (point /). It is clear from this that at about
1870 the resolving power of the compound microscope had al-
ready attained a very high value. It is, indeed, very interesting and
instructive, that an entirely new microscope constructed in one of the
most famous factories in the world yielded exactly the same curve for
its resolving power as the Hartnack instrument which was made about
65 years previously!

We may summarize these comments on the resolving power of
the microscope as follows: From 1700 to 1800 only the construc-
tion and the mechanical arrangement of the simple and of the com-

pound microscope were improved. The optical capacities however,
show hardly any improvement.

The simple microscope is. during this period, far superior in optical
respect to the compound one. which explains why scientific observers
invariably fall back on the former type of instrument for their most
important investigations. The successful construction and the de-
velopment of the achromatic objective opens a period of increasing
resolving power of the compound microscope. At about 1830 the
compound microscope definitely outdid the simple microscope, which
from this time onwards loses its leading position and is nowadays
only used as a dissecting microscope or as a magnifying glass.

In this connection we may perhaps once more draw attention to
the remarkable fact that, as regards optical powers, the van Leeuwen-
hoek microscope (A. 1) must have been one of the best micros-
copes ever made before 1830. It is therefore no wonder that van
Leeuwenhoek, possessing all the qualities of a keen observer was
able to make such startling discoveries with this instrument, that up
to the present day the scientific world is still amazed by them. Nor
is it to be wondered at, that their reliabihty and correctness were
formerly often doubted, for the simple reason that they could not be
repeated.

Anthonie van Leeuwenhoek (1637—1723) was undoubtedly the
pioneer of those sciences dependent on the microscope for their data.
For, at a time when, as yet, only the rudiments of the simple,
as well as of the compound, microscope existed and therefore only
the most primitive instruments were at his disposal, he suc-
ceeded in making extremely interesting discoveries. The reliabihty,
however of his observations was often doubted, then and later,
simply because no one was ever capable of repeating them. It was
considered next to impossible that with such a poor outfit — a very
small lens, which he had ground and polished himself, let in between
two roughly finished brass plates, and some rough arrangement for
focussing — he should have succeeded in observing protozoa, bacteria,
cilia, etc. Even nowadays the scientific world is still amazed at his
having obtained such important results with such simple means. And
again and again one meets with the opinion that van Leeuwenhoek
must have had better means at his disposal as well. Quite recently,
even, the same view has been put forward in this matter and it has been
suggested that van Leeuwenhoek must have been acquainted with

It is, of course, very probable that this phenomenon was actually
observed by him, as the present writer is quite willing to admit
but it is not at all necessary to assume that van Leeuwenhoek
must, purposely, have made use of it for his observations. Measure-
ments of the optical powers of the small microscope, described
under A. 1. show that this instrument even in its present condition,
with the lens badly scratched on the side of the object, is capable of
resolving, with a magnification of 270 the line structure of a grating
of which the spacing is 1/700 mm; one may safely assume that, when
in good condition in van Leeuwenhoek's time, its resolving power
must have been considerably higher. This means that this little instru-
ment must have surpassed in optical capacities any of the compound
microscopes of the 18th century and that not until the beginning of
the 19th century, some, though not many, instruments of more effi-
ciency arc to be found. Besides, it is not quite certain that the micros-
cope in this collection is the best of all he ever made. It is only

1) Cp. C. Dobell: ..Antony igt;an Leeuwenhoek and his little animalsquot;, pg. 332.

the strongest among those still left of the 250 microscopes made by
him, which existed at the time of his death.

Van Leeuwenhoek possessed all the qualities that go to make a
first-rate observer: keen eyesight, ingenuity and discrimination and,
undeniably, an indefatigable patience without which he could never
have worked with such clumsy apparatus at all. Moreover, his skill in
grinding and polishing lenses must have been exceptional. And yet
even all these excellent qualities do not explain his outstanding

success. This can be only fully understood by taking into account
the fact that he used exactly the type of microscope, which by its
high resolving power made his discoveries possible.

If, at that time, the compound microscope had already offered
the misleading advantages of a much more convenient manipulation
and its apparent superiority over the simple microscope, instead of
being still at the beginning of its development, and if van Leeuwen-
hoek should thereby have been induced to prefer the former type to
the latter he would never have obtained his startling results. In short,
he made his discoveries not in spite of, but thanks to, the fact he
made use of a primitive simple microscope.

This small instrument consists of two very badly finished brass
plates rivetted together and measuring about 4.5 X 2.5 cm- (fig. 2).
Between them a very small lens is fitted, having an effective diameter
of 0.5 mm. For examination, the object is stuck on a small point.
This point can be removed, which suggests that, originally, the
instrument was occasionally used with object-holders of a different
shape. What kind of object-holders these may have been is not known.
For focussing, the distance between the point and the lens can be
varied by a screw. This screw is 1 cm long; it has only 11 windings in
all and of very bad workmanship at that! Since moreover, the focal
length of the lens is very small, it is clear that the actual focussing
is an extremely tedious affair!

the object possible, the brass piece which carries the object-point is
attached to a long screw running parallel to the plates- The female
screw is in the shorter arm of a brass angle-piece, of which the longer
arm can turn round another screw, by which it is attached to the
brass plates. By this arrangement the object can be made to move
in all directions. A coarsely finished leather case belongs to this in-
strument.

As regards the lens, it is bi-convex. the radii of curvature are
± 0.75 mm; its greatest thickness it 1.1 mm. (fig. 3). The brass

plates between which it is fitted serve
at the same time as diaphragms; the
aperture on the object-side is 0.5 mm,
on the other side 0.8 mm. The dis-
tance object-lens is about 0.5 mm. For
the numerical aperture a value of
about 0.4 was found. The theoretical
resolving power is 1 At, but in practice,
details not less than V700 m™ apart,
are still seperated. The magnifying
power of the lens is X 275.

scratched rather spoils the image, which therefore is doubtlessly less
satisfactory now than when van Leeuwenhoek himself used the in-
strument. Yet structural details, the size which is somewhat more
than 1 iM are still resolved; coloured bacteria of a size between 1 and
2 u, can be seen clearly, and living bacteria measuring about 5

Fig 4 shows a microphotograph of a few diatoms. 1 he magni-
fication used in this instance was X 200; the actual length of the
side of the triangle in the figure is 0,18 mm.

For a very complete description of our instrument see:
P Harting, Het microscoop III, pg 43—44.
P. H. van Cittert. Proc. Amst. 35. 1062, 1932; 36, 194, 1933.
P. H. van Cittert, Natuur en Mensch, 53, 136, 1933.

The workmanship of this instrument (fig 5) is much better than
that of the original one. The construction of the objectholder is a to-
gether more solid and better finished. Its motion too can be better
controlled. The size of the instrument is X 15 cm-.

Originally, the lenses belonging to it were 'quot;^erchangeable one
with another At present, however, there is only one lens left having
a magnifying and a resolving-power of X 30 and Vioo mm re-

■'^Thrmkroscope is not signed. To judge from its decorative designs,
however, which remind one strongly of Joblot, its construction, very
probably, dates at about 1700.

The authenticity of this instrument is testified by the trade-mark
of the van Musschenbroek's viz. quot;the oriental lampquot; and by the arms
of Leyden. It is, in fact, more hke an ordinary magnifying glass to
which a movable object-holder is attached, than like a real micro-
scope (fig. 6). The various lenses, all of which have wooden mounts.

Johan van Musschcnbrock (1660—1707). who made this instrument, and his
brother Samttcl Joostcn van Musschenbrock were instrument-makers at Leyden.

can be pushed so as to fit tightly on a brass spike. The object-holder
is attached to the lower end of the spike by means of three ball and
socket joints which allow of the displacement of the object in all

The object-holders at present accompanying the instrument are
a wooden disc and a brass mount for holding capillary-tubes.

magnifying-powers X 8. 15 and 30. The last one resolves Vh,o mm.
This type of microscope is a.o. described, (resp. illustrated) in:
Ledermüller II, pg 56 resp. Tab XXXII.
Harting III, pg 48 resp. pi. I, fig. 10.
Petri, pg 44—45.
Clay and Court, pg 37—38.

Both of them were famous as designers and constructors of microscopes and
vacuum-pips. Johan's sons, ]an and Pefrus .an Masschcnbrock were both Jar^ou^^
too The former L an instrumentmaker at Leyden and as 's-Gravcsandc s collaborator
the lauer aTa professor of Physics in various universities, including Utrecht and
Leyden (cf C. A. Crommelin. Physics and the Art of Instrumentmakmg at Leyden
in the 17th and 18th centuries.)

This instrument (fig. 7) is remarkable for its object-holder, which
consists simply of a wire spring. For focussing, this spring is pressed
by hand toward the stem. The power of the lens is X 15. A card-
boardtube serves as a case for this very primitive instrument

Ledermüller II, pg 55 resp. Tab. XXI.
Harting III, pg 40 resp. pi. 1 fig. 2.
Petri, pg 40. 41-

This type of microscope was constructed in 1694 by Hartsoeker. i)
In 1702 after it had been slightly altered, Wilson introduced it
successfully and made it more popular. Its chief feature is its very
compact build. It consists of a short brass tube which can be attached
either to a handle or to a fixed stand. The small lens, mounted, either
in wood, brass or ivory is screwed in at one end of the tube. The
object is mounted in glass or between two small plates of mica which
are fastened together in ivory or horn. For examination it is pushed
between two brass plates which can be slid along two grooves of the
tube. The position of these two plates relative to the lens can be varied
by turning a second brass tube screwed in at the other end of the first
tube. This second tube sometimes contains a condenser.

In order to examine an opaque object this is stuck outside
the instrument on a sharp point or in a forceps clamped between
the two plates. The lens is then brought in the right position over
the object by means of a lens holder made especially for this
purpose. For a description, resp. illustr. of the screw-barrel micros-
cope see, among others:

1) Nicolaas Hartsoeker was born at Gouda in 1654. He settled as a maker of
microscopes in Rotterdam but in 1684 moved from there to Paris where he lived
for twelve years and became very well-known for his capacities as a grinder ot
lenses and as a physicist. In 1697 he was appointed teacher of physics to Czaar
Peter the Great.'and on this account the town of Amsterdam put a small l^boraWry
at Ms disposal. Later on he was appointed professor in Heidelberg and finally
cpttlpH down in Utrecht where he died in 1725.nbsp;_

quot;quot; Gerquot;?CraaLr or Grander lived from 1738 till his death in 1^55 at Groningen.
No further particulars concerning his profession are to be found in the archives.

The accessories belonging to it are four strong lenses provided with
ivory protection-caps and two weaker lenses, object-holders for the
examination of opaque bodies and a small tube containing various
objects. All these things are kept in a shagreen leather case.

Accompanying the microscope is a list written by hand giving the
various focal length's and magnifying powers of the lenses and also
an inventory of the objects. The respective magnifying powers and
resolving powers of the various lenses are:

This instrument (fig. 8) is signed quot;Culpeper fecitquot;. Of all the
accessories which belonged to it only one lens is left. Its magnifying
power is X 18 and its resolving power Vioo mm.

The microscope is attached to a stand which is fixed on a mahogany
box. Accompanying it are three lenses with powers X 15. 25 and 40.

This instrument is signed quot;C. i^an Wijk fecit Utrecht 17831) It
was presented by the Foundation of Renswoude. (together with other
instruments, some of which also made by van Wijk) to the Museum
of the University of Utrecht

This instrument has a stand fixed on a small wooden box (fig. 9).
It is signed quot;]acobus Lommers fecit. Utrecht 1760'-^). Two lens-

which had hi.Ti trained as instrument-maker, first at Utrecht, and later on m 1 ans.

holders belonging to it are still left, but only one of them is fitted with
a lens. Both holders are threaded so as to make it possible to screw
a short tube with an eye-piece on to the holder. By this device the
simple microscope could easily be altered into a compound one This
extra eye-piece tube is now missing. In the catalogue, dated 1839, ot
instruments belonging to the Physical Laboratory our instrument is
described as a compound one and Harting also mentions the said tube
in his book. (Harting III pg. H4).

This microscope, which can be used either attached to a handle or
fixed on its wooden box bears the signature quot;ƒ• G. Brinkman fecit
Bremenquot;. Accompanying it is the complete set of accessories, viz.
lens- and object-holders for opaque objects and 5 lenses. The
respective magnifying and resolving-powers of the lenses are:

This small instrument can, like the one described under C. 5, be
used in two ways, either attached to a handle or screwed on to a
stand fixed on a small wooden box. The illuminating mirror is missing.
The focussing differs from that of the ordinary type and is here
effected by moving the lens relative to the object by means of a screw.
The accessories accompanying it are:

of liquids and living objects,
and 3 lenses with powers X 12. 25 and 40. of which the last one

married in 1717. In 1743 the astronomical instruments of the University of Utrecht
were placed in his charge. In 1747 he appears to have established himself as an
instrument maker. On account of his high capacities in this line he was ottered
the citizen-ship of Utrecht free of cost. He was. very likely, connected with the
..Theatrum Physicumquot; of the University of Utrecht. Various instruments made by
him are now in the collection of the Utrecht University Museum. (Cp. U. A.
Evers. Maandblad van „Oud Utrechtquot; 3, 27. 1928).

About the year 1750 the Englishman Cuff began to construct
microscopes of a different design. Its advantage over the screw-
barrel model was the more convenient way in which the object could
be handled. This accounts for its holding its own for such a long
time as a standard model for the construction of microscopes. Even
the dissecting microscopes of today are still built on these lines.

The main feature of this instrument is the fixed object-stage which
is attached to the supporting-pillar. The latter may or may not
be fixed to the box of the microscope- Underneath the object-stage
is the illuminating-mirror and above it the lens. The lens is adjustable
with respect to the stage in various ways either by simple moving it
up and down by hand, or by means of a screw, or by rack-and-
pinion motion.

In the 18th century two types of instruments were distinguished,
viz. the quot;aquaticquot; and the quot;botanicquot; microscope. In the first type the
lens was capable, apart from its up and down motion, of a motion
sideways, parallel to the plane of the stage. This made it possible to
search a drop of water for protozoa and suchlike objects. The
quot;botanicquot; lens could only move up and down. A description of a
probably genuine Cuff microscope is given under H.l.

For description, resp. illustration of the original Cuff microscopes
the reader is referred to:

This instrument, which is not signed, was made by Jacob Huisen ')
for the Theatrum Physicum of the Utrecht University and delivered
on October 2nd 1758 as is shown by the books (accounts) of the

Jacob Huisen was born at Stralen. From 1739 until the time of his death
1792 he was an instrument-maker at Utrecht. In 1750 he obtained the citizenship
of Utrecht free of' cost on account of his great merits in his profession. His son
Hendrik Huisen was later on connected with the Theatrum Physicum of the
University of Utrecht. A few more instruments belonging to the university collection
are also made by this ]acob Huisen.

The focussing is effected by a rack-and-pinion motion. The rack
itself is pressed into the stand by means of spring (fig. 10). Among

the accessories accompanying the instrument arc 10 lenses of various
powers, one of them is very strong, two others are fitted with a
hollow metallic mirror for illuminating opaque objects from above,
(the so-called Lieberkuehn mirror). Only 5 of the lenses are in a
satisfactory condition. Their magnifying and resolving powers are
as follows:

This microscope is similar in every respect to the one described
under D. 1. The 8 lenses belonging to it, have the following magni-
fying and resolving powers.

This microscope is supported by a folding tripod which suggests
a probable construction at about 1800. The stand is connected to
the foot by a compass-joint and can therefore be made to incline.
The focussing is effected by means of a rack-and-pinion motion.

Accompanying the instrument is a simple lens, (magn. p. X 15),
which, however did not originally belong to it as is evident from the
fact of its being threaded.

quot;Charles Chevalierquot;
quot;Ingenieur Opticienquot;
quot;Palais Royal 163. Parisquot;.

In 1835 the „Natuurkundig Gezelschapquot; (Physical Society) at
Utrecht bought it for ƒ 81.50. Its general build is mostly on the
same lines as Cuff's original model (fig. II). It was designed by
Chevalier and an article about it was published in the Ann. d. Sc.
Nat. 1833. A copy of this article belongs to our instrument. The
focussing is done by an up or down rack-and-pinion motion of
the lens-holder. Under the stage a cone carrying a rotating dia-
phragm with 6 apertures is attached to a folding hinge.

From the accessories belonging to the instrument two doublets
are left, viz. No. 3 of which the magnifying and resolving power

These same doublets were examined by Harting. As regards the
magnications he obtained the same results. The resolving powers
however which he found were 1/450 quot;im resp. 1/950 mm. from which
it is clear that these powers have greatly diminished 1) (Cp. Harting
III p. 273).

Harting III page 103, resp. pi. Ill fig- 1.
For further data concerning Chevalier's doublets see:

1) The space between the lenses of doublet No. 5 was full of verdigris and the
lenses themselves have been obviously impaired by it too.

This microscope shows some strong deviations from the original
Cuff type. In a flat rectangular hollow pillar, fixed on a round foot,
a brass plate can be screwed up and down. The lens holder is
attached to the top of this plate (fig. 12). There is only one lensi
left with a power X 15. This instrument was presented to the
University Museum by the Foundation of Renswoude and was
probably the work of one of the wards of that foundation.

This instrument bears the signature quot;Dollond Londonquot;. It was
bought by the Physical Laboratory for ƒ 100 early in the 19th.
century. Its construction differs greatly from that of the ordinary
Cuff type (fig. 13). The lenses are mounted between two small brass
plates which can be slid on the main pillar and can then be screwed

up and down with respect to the stage. The stage itself can be
centrally adjuste;d. This is all contained in a small red morocco leather
case. Among the accessories of this instrument are four lens holders,
only three of which, however, are still fitted with a lens. Their
magnifying powers and resolving power are respectively X 185 and

Veoo mm; X 330 and Vsoo mm and X 480 and Vsoo mm. Harting
gives for the missing lens a magnifying power X 77.

A cursory mention of the instrument is made by f-farting in III
page 81. where he gives the powers of the lenses and comments upon

the X 'ISO lens as being the strongest lens obtained by grinding and
polishing he had ever seen.

As regards its general shape this resembles the Zeiss microscope,
described and illustrated in Petri (pg. 95—96). The only difference
is a wooden foot instead of a brass one. To the instrument belongs a
case containing two doublet lenses of the Chevalier type with mag-
nifying powers X 30 and X 60. Both of them resolve V-joo mm.

two plano-con\jex lenses, the focal length of which are in the ratio
3:1. The lenses are placed a short distance apart one above the
other and have their plane surfaces turned towards the object. (Cp.
Harting III pg. 77 resp. pi. II, fig. 9).

Wollaston designed and constructed a single microscope as well,
which he fitted with a peculiar illuminating apparatus. A brass tube
screwed on to a wooden box contained a fixed illuminating lens
which concentrated the hght from the mirror at the lower end of the
tube on the object. Later on, Dollond made similar instruments but
with an adjustable illuminating lens and an object stage capable of
central adjustment.

This instrument, signed quot;Dollond Londonquot;, was bought by the
Utrecht quot;Physical Societyquot; in 1835 for the sum of ƒ 120. It is fitted
with the illuminating apparatus mentioned above and with a centrally
adjustable stage. (Fig. H). Accompanying the microscope there are
two doublets with magnifications X 200 and X 300, and with
resolving powers V400 mm ^nd Vsoo respectively.

This instrument was made according to special indications given
by Harting. The characteristic features in which it differs from the
original Wollaston construction are a larger illuminating mirror, an
adjustable illuminating lens, a revolving diaphragm under the object-
stage and an ivory micrometer scale fixed to the focussing screw.
(Fig. 15).

Harting gave a very complete description of it in Bulletin de Sc.
phys. et nat. 1, 354, 1839 and a less detailed one in Harting III
footnote on pg. 78—79.

Harting worked with this instrument a great deal though he did
not actually use the doublets. Instead of these he fitted it with small
glass beads mounted in platinum foil. In his book he describes at
some length how these beads can be obtained by melting (Harting
III pg. 58—59). Accompanying the microscope there are still a
number of these beads, only some of which are complete with mount,
and differing greatly, amongst each other, in strength.

This small instrument consists of a short wooden tube in which
a lens, mounted in wood, can be screwed up and down. In the base
of the tube is a small square opening, the sides of which measure
exactly two quot;Rijnlandsche lijnenquot;. This instrument was made for
counting the number of threads contained in two quot;Rhineland linesquot;.
Its magnification is X 8-

This is simply a short glass tube in which a lens (power X 4) can
be screwed up and down. It was made for the purpose of examining
living insects.

This is a bi-convex lens mounted in silver. The plane of the
object coincides with the surface of the lesser curvature. The lens
is therefore always focussed on its own less-curved end so that for
examination the object must be placed right up against this end.
Its power is X 35.

With a view to reducing the spherical aberration, Coddington
devised the grinding of a groove round a glass sphere. By this
contrivance only those rays which have passed through the lens
near its centre can contribute to the formation of the image. The

lenses were mounted on short brass tubes in which they were kept
when not in use. (Fig. 16).

Both samples are made by Gary. Early in the 19th century the
Utrecht Physical Society became the owner of them for the sum
of ƒ. 19.20 for both. Their magnifications are X 22 and X 35. The
strongest lens resolves Vioo quot;im.

mater al. The foot m which there was usually a drawer remained
then the only part made of wood.nbsp;remained

Baker, pg. 15—21 resp. pi. III.
Adams, pg. lO-l—106 resp. pi. IV.
Harting III, pg. Hi resp. pi. IV. fig. 7
Petri, pg. I49_i52.

to support the body-tube in which the microscope-tube can be shd
up and down (fig. 17).

The instrument itself is not signed, but the Culpeper quot;tradecardquot;
is fastened in the pyramidal case belonging to it.

The microscope is accompanied by the usual accessories such as:
spring object holder

illuminating lens screwed on to the stage
ivory cone with diaphragms
objectglasses in brass mounts
fish plate
live box.

The microscope-tube is marked with dotted lines indicating the
positions of the tube with relation to the body-tube required for
sharp focussing with the various objectives. The 5 objectives be-

Like the instrument just mentioned under G.l. this one is built for
the greater part of wood and cardboard- It differs from the first how-

ever, m that the foot, which has a drawer, is octagonal and that it
has one set of three legs extended so as to support the body-tube
instead of two sets of three legs alternating at the stage. The case
is missing. The microscope is exactly similar to those figured in Clay
and Court, pg. 118 fig. 78 and in Cat. R. M. S., pi. V A 7. The
accessories still left are: a spring objectholder and a shaft with sharp
point and clamp; special clips for small glass tubes are attached to

the stage. The five objectives belonging to the instrument have the
following magnifying and resolving powers:

Three brass legs fixed on a round wooden foot support the body-
tube of this instrument, made very primitively of cardboard orna-
mented with a flowery design- The lenses belonging to it are fitted
in ivory mounts (fig. 18). The magnifying power is X 15. Besides
these, there are an object-holder with spring-clamping and a pyra-
midal case.

This is one of the many instruments of wood and cardboard made
in Germany during the 18th century (Fig. 19). They were mostly
manufactured by preachers. (Cp. U. 5).

When the microscope-tube is drawn up to a certain mark out of
the body-tube the magnifying and resolving power of the instrument
are X 80 and Vioo mm. The mark IM is branded into the bottom
of the foot.

This instrument is constructed on lines exactly similar to those of
the original Culpeper microscope but contrary to the latter this one
is. with the exception of the foot, made entirely of brass. The ac-
cessories accompanying it are:

wooden slide for objects mounted in ivory caps
clips for small glass tubes
pyramidal case.

Originally there were 4 objectives belonging to the instrument.
The lenses of those numbered 1 and 3 however are now missing,
while the lens of number 2 is damaged. The power of the remaining
number 4 is X 30.

This instrument is mounted on a square foot, containing a drawer.
It is kept in a pyramidal case. Its accessories are:
object-holder
illuminating lens
clips for glass tubes

sliding tube fitted with a Lieberkuehn mirror
brass diaphragm cone
small pointed shaft with forceps
and in addition. 5 objectives of which the magnifications and resol-
ving powers are:

The image obtained with No. 1, is, considering, a very good one-
G. 7. Brass Culpeper microscope.

sliding-tube fitted with a Lieberkuehn mirror
brass diaphragm cone
fish plate
live box

The microscope bears the inscription quot;Urings fecitquot;. The pyra-
midal case in which it is kept is marked with the tradecard of the
dealer and gives the following information concerning him, in quaint
old Dutch:nbsp;,

quot;Anthonie Ciquino woond in de Nes, in de Weyde Lombaertsteeg,
quot;in de Drie Weerglazen, 't Amsterdam.

quot;Maakt, Verkoopt en Versteld alle Zoorten van Barometers en
quot;Thermometers, Verkoopt ook veelderlei Zoorten van Verrekijkers,
quot;Optica-, Gezigt- en Experientie-Glaazen, Tot een civiele Prijs.quot;

quot;Anthony Ciquino lives in the Nes,quot; (an old part of the town of
Amsterdam) quot;in the broad Lombaert-alley, in the quot;Three Weather-
quot;glassesquot; at Amsterdam.

quot;Makes, sells and repairs all kinds of barometers and thermometers,
quot;sells also a great variety of field-glasses and glasses for optical
quot;experiments, at moderate prices.quot;

The accessories accompanying this microscope are:
economyglass
spring object-holder
sliding tube with Lieberkuehn mirror
fish-plate

handle for the objectives, when used as ordinary mag-
nifying-glasses, and, finally. 5 objectives. The field-lens of the
microscope however is missing and for this reason there would be no
sense in determining the magnifications and resolving-powers.

The two main drawbacks of the Culpeper type of microscope are
he inconvenient position of the stage between the three supportinq-
legs, which interfere with the adjustment of the objects and of tL
accessories, and the primitive way in which the focussing is effected
J hese induced Cuf[ to devise and construct a new model- The
characteristic feature of this instrument, which, like that of Cul-
peper became exceedingly popular, is the attachment, by means
of an arm, of the tube to a rectangular pillar which can be slid along
another similar pillar, fixed on the foot, while gripping it tighty For
focussing, a rough adjustment is obtained by shifting the sliding pillar
by hand to its approximately correct position. To facilitate this, num-
bered notches are engraved on the fixed pillar indicating the posi-
tion required when the objective with the corresponding number is
used. After clamping the sliding pillar to the fixed one, the final
focussing is effected by means of a screw. C«// made the stage
in the shape of a Maltese cross, in the corners of this cross are holes
m which the condensing lens, the fish plate etc. can be fixed On
the snout (microscopic-tube) slides an outer tube on to which the
lieberkuehn was screwed. Numbered notches on the microscope-tube
denote the position of this outer tube required to concentrate the
reflected light on the objects underneath. This type of instrument
IS described, resp, illustrated in:

Adams, pg. 89—92 resp. pi. VII A.
Harting HI. pg. 142—143 resp. pi. IV fig. 8.
Petri, pg. 153—154.
Clay and Court, pg. 136—154.

This instrument differs greatly from the general type described
above. It IS mounted on an oval brass plate which is fixed on a
mahogany foot (fig. 21). The stand is attached to the brass foot by
means of a compass-joint. The microscope itself which is made of
wood and of shagreen covered cardboard can be replaced by a simple
microscope and is illustrated as such in Clay and Court fig. 42 and
in Petrus van Musschenbroek: Introductio ad Phil. Nat. II, Tab. XLV.

Neither the instrument nor the case are signed. The Science Museum
in London however, is in the possession of a model exactly similar,
of which the case, too, has precisely the same division, and this case
is signed quot;Cuf/quot;. This practically guarantees the authenticity of our
instrument.

The illuminating-mirror as well as the stage and the body itself
can be folded back against the pillar. The microscope has aquatic
motion. The illuminating-mirror is hollow on the one side and plane
on the other.

As a simple microscope four objectives belong to it, fitted with
ivory protection caps. These four can be combined by screwing one
on top of the other. This arrangement, however, gives very poor
images. The magnification and resolving-power of the various
lenses are

As a compound microscope it has a sliding tube and two objectives,
both of which are constructed in lieberkuehns. When the tube is slid
in, the magnifications of the objectives are X 45 and X 100, the
resolving power of both of them is i/ioo mm. On comparing this power
with the values for the simple microscope the superiority of the latter
is evident at once. Moreover, the images given by the compound
microscope are strongly chromatic.

The accessories belonging to the instrument are: live box fish plate
and a screw to fix the oval brass foot directly on the table.

This microscope is mounted on a square wooden foot with a drawer
in it (fig. 22). It is signed quot;Geo Sterrop, makerquot;. Its accessories are:
two object-holders, with spring clamping,
a black and white disc for putting the object on.
a ground glass object carrier,
an illuminating lens
a brass diaphragm cone
a small sharp pointed shaft
a lieberkuehn tube
a fish plate
a live box

In addition it has 6 objectives of which the magnifying and resolving
powers are resp.

This instrument which bears no signature is remarkable for its
stage which differs from the usual type by its oblong shape. A further
curious detail is the mounted condenser, belonging to the instrument,
which can be fitted in the hole in the stage. The object holder with

spring-clamping and the diaphragm-cone are combined to make one
single piece. Further accessories are:

This instrument is signed quot;Lincoln, Londonquot;. Its strongest feature
IS Its resolving power which far exceeds the average of the other
non-corrected compound microscopes.

The accessories belonging to it are:
object-holder with spring-clamping
small sharp-pointed shaft with forceps and a black and

white disc
brass diaphragm cone
lieberkuehn tube
illuminating lens
fish plate
live box
glass tubes

pyramidal case with drawer
and 6 objectives with the following magnifying and resolving powers:

This instrum^ent is signed quot;B. Martin et fils, fecitquot;
In strong contrast to H. 4. the resolving power of this instrument
remains far beneath the average. Besides, of the 5 objectives belonging
to It, 4 are, practically speaking, equally strong. Its accessories are:

object-holder with spring clamping
lieberkuehn tube
brass diaphragm cone
revolving object-holder

small sharp pointed shaft with forceps and a black cap
double illuminating mirror
and besides 5 objectives of which the magnifications and resolving
powers are respectively:

This is a very primitive instrument differing greatly from the stan-
dard type. It is in all probability the work of some of the wards of
the quot;van Renswoudequot; foundation. A vertical grooved stand of brass
is fixed on a round wooden foot. In the groove the arm bearing the
microscope can be slid up and down and is adjustable by means of a
screw. The instrument is constructed without a field lens. The illu-
minating mirror is missing. The remaining accessories are a spike
for fixing the objects and four objectives. One of the latter however
is without a lens. The magnifying powers of the others are X 100,
56 and 32, The images obtained by them are very poor. The strongest
objective is hardly able to resolve Vioo mm. To the instrument there
belongs a very coarsely finished pyramidal case with a drawer.

This instrument is remarkable for the way it combines some features
of the Cuff microscope with some of the Culpeper type. A round
brass pillar is fixed on a square foot with a drawer in it. To the
pillar the stage is attached sideways and also the body-tube in which
the microscope-tube, exactly as in the Culpeper type, can be slid up
and down, with this difference that the sliding is not effected by
hand in this case, but by rack and pinion (fig. 23).

No. 1 gives a distorted image. The image obtained with No. 2. is
exceedingly poor. Its present lens was evidently put in at a later date
and did not belong to this microscope.

This is more or less similar to the one described onder H. 7. The
object-holder with spring-clamping and the diaphragm-cone are made
in one piece. Various accessories are missing; all that is left of them
is a small sharppointed shaft with forceps and four objectives with
the following particulars:

The objective lenses are plano-convex, their convex surfaces how-
ever are turned towards the side of the object.

About the year 1770, Dellabarre built a microscope which, accord-
ing to him, had many advantages over the existing types. In the first
place, according to him, the images were achromatic owing to the
fact that the eyepiece of his construction consisted of several lenses
made of different kinds of glass. In the second place, the numerous
combinations made possible by intercombining four ocular lenses,
three objectives and a long or short microscopic-tube, were supposed
to offer many advantages too. According to the inventor, the images
were splendid in quahty and a magnification of 231102^2000 could
be reached. This enormous value was meant as a three-dimensional!

In reality, however, the instrument did not nearly achieve what it
was supposed to. The four ocular lenses were all of them bi-convex,
and could therefore never be combined so as to form achromatic
sets. Besides, if one tries to obtain higher magnifications by combin-
ing ocular lenses of the strength of 80 dioptries instead of by making
the objective stronger, one can never expect an increase of the
resolving powei.

The microscope was constructed as follows: On a tripod was
mounted a square brass stand along which the illuminating mirror
(plane on one side and hollow on the other), the condenser and the
stage could be slid. They could all three be folded and rotated side-
ways out of the optica] axis. The up and down motion of the stage
was effected by rack and pinion. The microscope, clamped in a ring,
hung at the end of an arm which was attached to the stand so as
to be capablc of quot;aquaticquot; motion. The microscope was comparatively
short, it could however, be lengthened by an auxiliary tube. Four
ocular lenses and 3 objectives belonged to the instrument. The four
ocular lenses could either be combined into one system, or each one

of them could be made to play the part of a field-lens while the
other three could be combined in various ways to an eyepiece. Over the
eyepiece an eye-ring was fixed, but as early as in the translation of
Baker's work it is stated that the latter was practically never used,
and indeed, observations made with the microscope described below
under I. 1. confirmed the utter impractability of this eye-ring!

The upper part of the metal stand together with the microscope
and the stage could pivot round a compass joint, so that the instru-
ment could be used in a horizontal arrangement as well. The whole
instrument made an unwieldy impression and its mechanism left much
to be desired!

The construction of this instrument agrees in every way with
Baker's description, mentioned above. The various parts are even
marked with the same letters as those given to them in the descrip-
tion, (fig. 24). The accessories include a large Lieberkuehn mirror
and an object-holder of a special make to be used in the horizontal
arrangement. Everything is contained in a mahogany box. Three ob-
jectives and four eyepiece lenses belong to the instrument as well.
Although Dellabarre, in his original description, states emphatically
that the objective lenses are plano-convex, with their plane surfaces
turned towards the object, in reality the lenses here are bi-convex-
The eyepiece lenses are all different from each other. The approxi-
mate values of their optical data are as follows:

(The refractive indices arc computed from the directly measured
values of the radii of curvature and the focal lengths.)

given in the direction from top to bottom. The eyepiece lens IV has a
strong green colour.

The perfectly useless eyering and the equally superfluous diffe-
rences between the various ocular lenses have been omitted from this
microscope. It is fitted instead with a fixed field-lens of focal length
5,3 cm and 3 identical eyepiece lenses, focal length 3,8 cm, which can
be intercombined. Their refractive index is about 1.6. The double
illuminating mirror is made of speculum metal. Further accessories are:
Lieberkuehn mirror
shaft with forceps and sharp point
pyramidal case.

Only one objective is left. With 3, 2, resp. 1 eyepiece lens the magni-
fication is X 27, 23 and 15 respectively. With none of the magnifi-
cations i/joo mm is resolved.

In the beginning of the 19th century the EngUsh instrumentmaker
Cary constructed a small microscope which became highly popular,

especially in England. The microscope-tube, the upper part of which
was cyhndrical and the lower part conically narrowing was fixed
rigidly to the stand. The focussing was therefore effected exclusively
by the up and down motion of the object by means of rack and
pinion. The microscope was fitted with various objectives which
could be used either separately or in combination. The eyepiece lens

and the field-lens were fitted to form, as is still done nowadays, one
single sliding piece- For description see for instance:

This small instrument mounted on a round wooden foot bears the
signature ..Cary. Londonquot;, (fig. 25). To the lower end of the micro-
scope carrier is attached a small plane-convex lens in the centre of
a Lieberkuehn mirror. There are also three bi-convex objective lenses
and inside the microscope tube there is still another little lens with a
conical wooden mount. The mounting is however so primitive that
the adjustment of this lens in the optical axis of the instrument is
practically impossible. This complication makes all efforts to obtain
images of a fairly good quality unsuccessful. It is very doubtful whe-
ther this lens really belonged to the instrument originally at all.

The eyepiece is a doublet consisting of two bi-convex lenses.
When used as a simple microscope the lens (L) mounted in the Lie-
berkuehn gives a magnification X 24 and resolves V200

This microscope, of which the illuminating mirror is missing, is
mounted on a wooden box. Accompanying the instrument there are
three objectives allowing of combinations with magnifying and re-
solving powers as follows:

Like those of the instrument just mentioned some of these combi-
nations give strongly chromatic images too.

With the exception of the hoop bearing the body of the microscope
and of the stage, this instrument is made entirely of wood. The stand
is fixed on a large mahogany box; to this stand the brass hoop is

attached in which the microscopic tube can be made to sHde up and
down by hand. For sharp focussing the stage is adjusted by means
of a screw (fig. 26). The illuminating mirror is missing and of the
original objpctives only No 5. is left. Its magnifying power is X 40,
but the images are strongly distorted and it cannot resolve even so
much as Vico mm.

It is very much like the instrument described and figured in
Cat. R.M.S. pg. 201 resp. pi. 16. and
Clay ond Court pg. 194—197
only it is much less decorative (fig. 27). A square bar is fixed on a

folding tripod. The upper end of the bar carries the microscope which
can pivot on a joint. That bar can be inclined, according to need, by
means of a worm. The double illuminating mirror as well as the
stage can be made to slide along the stand-bar by means of rack and
pinion. The microscope itself is, optically speaking, remarkable:
between the field-lens and the objective is fitted another lens, a
bi-convex one, of power 4,5 D which is called the ,,between-lensquot;.
The distance objective—quot;between-lensquot; amounts to 6.5 cm. The eye-
piece consists of two lenses, 8 cm apart, viz: a plano-convex ocular
lens (power 16 D) and ditto field-lens (power 10 D) and can be
made to slide over a range of 6.5 cm, so that the distance field-lens

—between-lens can be varied from 5 to 11.5 cm. The between-lens was
evidently put in to intensify the influence of the field-lens, for it
enlarges the field of view at the cost of the magnification. Both eye-
piece lenses are mounted with their plane surfaces turned towards
the eye.

Of the objectives only No. 2 is left. The various optical data of the
instrument are:

All other accessories are missing except a loose triple object-carrier
that can be fixed on the stage.

This small microscope, elegantly finished off and contained in a
morocco-leather case differs in mechanical as well as in optical respect
from all the other microscopes of the collection.

On a folding tripod are mounted the illuminating mirror, and an
octagonal tube (fig. 28) in which a round steel rod can be made to
slide over a small range by means of a screw immediately above the
foot. Over this steel rod a brass tube can move up and down and can
be clamped tight to the rod at any desired height by a screw. At its
upper end this tube carries the microscope.

The coarse focussing is effected by moving the round tube over the
steel rod by hand and. after clamping it for the final adjustment, the
steel rod is moved by means of the lower screw in the octagonal tube.

The stage is attached to the octagonal tube; it can be removed and
replaced by an arm which carries a little shaft movable in all directions
and with a forceps at one end and a black-white disc at the other.

The microscope contains, besides the usual lenses, the quot;between-
lensquot;, mentioned under K. 2. This is a plano-convex lens with its flat
side turned up and fitted at such a height that the eyepiece is focussed
exactly on this flat surface so that the image of a micrometer if
placed on this surface is seen sharp, together with the image of the
object.

There were, originally, 5 objectives with the instrument. One of
them is mounted in a lieberkuehn mirror (L). The others were
marked 1—4. No 1. however, is missing. The, objectives can be used
as a simple microscope too. For that purpose an eye-cap can be fitted
above the objective in question.

Here is once more a convincing demonstration of the superiority
of the simple microscope. The same lens which as a simple microscope
resolves ^/loo miii- with a magnification of 19 is not able as part of a
compound microscope to resolve this ^/loo mm with a magnification
of 40.

It is mounted on a folding tripod. The microscope itself has aquatic
motion. The focussing is effected by rack and pinion adjustment of
the stage. The latter is fitted with two clips and an illuminating lens
is attached to it by means of a hinge and ball socket joint so that
it can be turned in any direction (fig. 29).

The eyepiece is a doublet of which both lenses are bi-convex.
When fitted in a special holder, included among the accessories, it can
be used separately as a simple microscope and. as such, its magnifi-
cation is X 17 and its resolving power i/ioo mm.

tube and is marked with a notch. When the eyepiece is drawn out
as far as this notch the 4 objectives belonging to the instrument have
the following magnifying and resolving powers:

Objective No 1. is plano-convex and its plane surface is turned
towards the object; the others are bi-convex.

Besides numerous accessories for dissecting purposes there is
a stray tube with an object-holder attached to it and in which a
second tube can be slid by rack and pinion. To the latter tube the
objectives and the eyepiece can be screwed on and the instrument
held simply in the hand.

To judge from its construction the date of this instrument must be
about the middle of the 19th century though it is not achromatized.
On a round metal foot two vertical bars are fixed between which
the stage can move up and down by rack and pinion. These bars are
connected at the top by a horizontal slab which carries a tube in
which the microscope tube can slide up and down. To this slab is
also attached a condensing lens which can move in all directions by
means of a double ball-socket joint. The 3 objectives accompanying
the instrument are bi-convex, the lenses of the eye-piece, however,
plano-convex, with their plane surfaces turned towards the eye. The
resolving power is considerably greater than that of the compound
microscope described above, a fact which must be solely ascribed to
the better workmanship bestowed on the lenses.

CHAPTER IV.
Achromatic Compound Microscopes.
L. Achromatic objective of Beeldsnijder.

This objective was found by Pro/. Harting among microscopes and
accessories in a box which had originally belonged to François Beeld-
snijder. 1 ) According to Harting it must have been made by Beeld-
snijder himself somewhere about 1791, a time when he was engaged
in the construction of microscopes. It consists of three lenses fitted
in a short brass tube, and of which the optical centres are very closely
collinear. The two outer lenses are bi-convex and are made of crown
glass, between them is placed a bi-concave lens of flint glass. The
first two lenses have focal lengths of 22 resp. 19 mm, the focal length
of the third one is 20 mm, the focal length of the system amounts
therefore to about 21 mm. The thickness of the 3 lenses together
amounts to about 4 mm. Their diameter is 6.5 mm. When combined
with the weakest eyepiece of Hartnack (Q. 3) it can resolve i/ioo
while the magnification is still as low as 20, an achievement which
cannot be obtained by any of the compound microscopes described
above nor exceeded by the simple microscope either.

François Gcrardzoon Beeldsnijder was born in 1755 and died in 1808. He was
a colonel in the Amsterdam cavalry, a member of the committee of Justice in that
town and collecter of burial rates of St. Anthony's churchyard. He used to spend
much of his time in experimenting in physics and mechanics as an amateur.

The Amsterdam instrumentmaker, Harmanus van Deyl (born in
1738), was the first to introduce achromatic microscopes on the
market. In a communication to the Physical papers of the Royal
Society of Sciences at Haarlem HI. 2nd. vol, page 133, 1807 (Natuur-
kundige Verhandelingen van de Koninklijke Maatschappij der Weten-
schappen te Haarlem UI, 2e deel, pg. 133, 1807) he states that he
and his father Jan van Deyl, (born in 1715, and died in 1801) had
already constructed an achromatic microscope as early as 1770. They
had, however not advertised their success, being at the time too busy
making achromatic fieldglasses (telescopes) and because they ex-
pected others would succeed ere long in the construction of the same
microscope.

Harmanus van Deyl then proceeds to give a description of the
achromatic microscope which he had just made for the market. The
stand was very sober in design; the utmost care, however was be-
stowed on the lenses. The optical equipment of the microscope con-
sisted of two achromatic objectives with focal-lengths n/io quot;duimquot;
(= 26 mm) and ^ quot;duimquot; (= 18 mm) and two eyepieces. The
objectives were composed of a plano-convex flint-lens and a bi-convex
crown-lens. The plane surface of the first was turned towards the
side of the object. The two eyepieces were bi-convex but their sur-
face on the side of the eye was considerably less curved than the
other one. The microscope-tube could be lengthened by drawing out
the inner tube. The magnifying power of the weaker objective com-
bined with the weaker eyepiece was, with the tube pushed in, X 25
and reached X 45 when the tube was drawn out (these magnifications
are determined for 20 cm distance). Combining the weaker objective
and the stronger eyepiece, as well as the stronger objective and the
weaker eyepiece, these values ranged from X 45 to X 80 and finally,
for the combination of the stronger objective and stronger eyepiece,
from X 40 to X 150.

In Harting III pag. 170—174 this instrument is described in detail.
According to Harting it was possible to combine the two objectives,
thereby increasing the resolving power so as to be able to resolve
even the third group of a Nobertplate (0.0016 mm).

It is accompanied by a very complete handwritten description. Its
mechanical construction is very simple and in many respects does not
reach the high standard of the instruments of the 18th century. The
illuminating mirror is fastened on a folding tripod, as is also a brass
bar in the groove of which the stage can be moved up and down by
means of a pinion. At the upper end of the bar the microscope is
attached in such a way that it can be moved by hand in any direction
over the stage (aquatic motion).

Accompanying the instrument there are also the two achromatic
objectives and the eyepieces. The weaker eyepiece, however, con-
tains a bi-convex lens with equal curvature on both sides; it, therefore,
evidently does not belong to the instrument; nor does the magnifica-
tion obtained with it agree with the one given in the accompanying
description. Strange to say, the instrument is constructed without a
field'lens. Further information concerning the objectives cannot be
given as they are mounted in such a way that they cannot be taken
to pieces. Cleaning the lenses was therefore out of the question and
the following measured resolving powers only represent a lower limit.
The images are indeed achromatic, only strongly distorted.

Its mechanical parts are much better finished off that those of the
instrument described under M.l. The microscope is not moved by

hand over the stage but by means of a rack and pinion and by a
worm (fig. 30). Contrary to the construction of M. 1 this instrument
is equipped with a field-lens, which, like the eyepieces, is bi-convex,
with its less-curved surface turned towards the eye. The two eye-
pieces are screwed on to this field-lens with tubes of different lengths.

The numbers in brackets are those given in the above-mentioned
communication (corrected for 25cm. distance).

The quality of the images is very satisfactory. They are achromatic
and not distorted. On comparing the resolving powers of this instru-
ment with those of the non-achromatic types, described above, it is
at once apparent that van Deyl's achievements mean a considerable
step forwards. His resolving powers reach the same order of mag-
nitude as those of the simple microscopes.

A very great improvement in the construction of achromatic ob-
jectives was made by the Itahan professor Amid (f 1862). He began
by trying to avoid chromatic aberration by constructing objectives
with concave mirrors instead of lenses (Katadioptric microscopes),
but about 1830 he began to improve the achromatic objectives. He
put an end to the method, which had gradually become general, of
making strong objectives by combining a number of weaker lenses,
each of which had been corrected separately as completely as possi-
ble. He, on the contrary, constructed objectives of which the separate
parts themselves still showed strong deviations, only they were com-
puted in such a way as to neutralize their impairing effects when
combined. This method made the correction of the objectives much
more satisfactory than before. Amid moreover, included in his consi-
derations the thickness of the cover-glass and he was the first to make
systematic use of immersion for the purpose of obtaining higher re-
solving powers. As a further improvement, he equipped his micro-
scopes with a large number of eyepieces which made alteration of
the magnifications possible without having to change the objectives
and without spoiling the central adjustment of the object.

Finally, he constructed his microscopes with the tube horizontal
which, in his opinion, facilitated observations considerably; he achie-
ved this by placing a reflecting prism over the objective.

It was bought by the quot;Natuurkundig Gezelschapquot; (Physical Socie-
ty) for f 500. A very complete description signed by Amid and dated
March 7th. 1836 accompanies the instrument.

It is constructed as follows (fig. 31): On a folding tripod is moun-
ted a brass stand along which a very large concave illuminating mirror,
and the stage as well, can be made to slide by rack and pinion. The
horizontal microscope is attached to the upper end of the stand. The
stage can be moved in two directions at right angles to each other.
These displacements can be measured with the aid of two micrometer-
screws of which the divisions correspond to 0.0031 mm and to

0.00246 mm (= 0.0001 inch) respectively. Directly under the stage
is fitted a cone with a diaphragm-wheel with three apertures. This
cone can be rotated out of the optical axis. There is, further, a small
ground glass plate capable of the same rotation. A plano-convex
condensing lens for the illumination of opaque objects is attached

to the microscope tube, and one of the objectives is fitted with a
Lieberkuehn mirror.

resp. pi. VII fig. 19), i.e. a mirror smaller than the pupil of the
eye; it was placed at an inclination of 45° behind the eyepiece.
Looking straight down it one could see via the small mirror into
the microscope, and along its edge on the table beyond.

2). A glass plate a few mm thick, which was placed like the
little mirror at an inclination of 45° behind the eyepiece (Cp. Har-
ting III pg. 435). By this means one could see the table through
the plate and, by the reflection of the front surface, into the
microscope. This kind of camera lucida could, naturally, only be
used with very strongly illuminated objects and with low magni-
fications.

3. The camera lucida of Amid (Harting I pg. 257 resp. pi V
fig. 85) consisting of a small perforated mirror likewise slanting
at 45° behind the eyepiece and an inverting prism underneath.
Observing horizontally, one looked through the opening into the
microscope and via the mirror at the table. The prism served to
erect the image reverted by the mirror.

Originally 5 eyepieces and 10 objectives belonged to the micro-
scope. The objectives numbered from 1 to 8, 10 and 12 could be
combined by means of two small cylindrical tubes, numbered 0 and
11 in the following ways;

8°

0	0	0	0
1	1	4	6
2	2	5	7
2	3	6	8

10 1	10
	11	0
	12	1

The only difference between the 4th and 5th system is that a
small Lieberkuehn mirror (also marked with 2) is attached at the
lower end of the combination 0, 1,2.

With the combinations 1° to 5° the thickness of the cover glass was
of no importance; the 6th required a definite, clearly determined thick-
ness, the 7th could be used without a cover-glass, while with the 8th
it was necessary to cover the object with a thin mica plate.

Amid gives the following magnifications for the distance from the
eyepiece tot the surface of the table (33 cm):

Unfortunately, of all these optical accessories only tube 0, objective
2 fitted with the Lieberkuehn mirror, and the eyepieces 1, 3, 4 and 5
are left. Although the objective 2 was not meant to be used without
one of the others the images obtained by it are exceedingly sharp.
Combined with eyepiece No. 1. the magnification is X 80, with
No. 3. X 200 and with No. 4. X 320. In all three cases it resolves
1/400 mm; a value which none of the microscopes described above,
compound or simple, can reach with a magnification of 80. With
eyepiece No 5., it is not easy to focus sharply.

Of the eyepieces, No 1. is a very long one; it consists of a plano-
convex field-lens and ditto eye-glass; the plane surfaces of both arc
turned towards the eye. No 3. is an Huyghenian eyepiece also fitted
with two plano-convex lenses. No 4. is composed of two plano-
convex lenses, one immediately on top of the other, whereas No 5.
consists of one single almost spherical lens. Amid remarks that this
last one is practically never used. The eyepieces 1 and 3 are provided
with spider-lines, used for measurements with the stage-micrometers.
The combination 6, 7, 8 was not originally included among the
accessories of the instrument in the price paid for it but were presen-
ted by Amid as an expression of his high esteem for Pro/. G. Moll
at Utrcdit. The microscope was originally provided with an arrange-
ment by means of which it could be used as a vertical and as a simple
microscope as well. This arrangement is now however missing.

Three members of the Chevalier family in Paris, namely, Vincent,
Charles and Arthur, won widespread fame in the 19th cent, as con-
structors of achromatic microscopes. It was Charles Chevalier, appa-
rently, who first thought of making stronger objectives by combining
a number of small lenses, each of which had been corrected separa-
tely. (± 1824).

It is kept in a mahogany case which serves as its foot when in
use (fig. 32). Along the square stand, which carries the microscope,
the illuminating mirror and the stage can be shd. The illuminating
mirror is concave on one side and has a plane surface of a smaller
diameter on the other. There are two interchangeable stages with
the instrument: a fixed one and a mechanical one after the system of
Tyrrell, (cp. Harting III pg. 397 and pi. IX fig. 11). Under the
table is a cone which can be rotated out of the optical axis and
carrying a wheel with 6 diaphragms. The microscope tube itself can
be pushed in or drawn out. The optical accessories accompanying the
instrument are 4 objectives and two Huyghenian eyepieces. Each
objective consists of a system of three small corrected lenses.

means of the Grayson rulings because its focussing required the
distance between object and objective to be smaller than the thick-
ness of the cover-glass of the testplate.

There are also two doublets with the instrument, by means of
which it can be used as a simple microscope, in which condition it is
practically the same as the model described under D. 4 and illustrated
in fig. 11. (Magn. and resolv. p. X 22 and i/ioo nim and X 37 and
1/200 mm resp.).

The construction is very much the same as that of a modern
microscope. The foot has the horse-shoe shape and the instrument is
jointed on to it, so that it can be made to incline The microscope is
carried by an arm fixed sideways on to the stage. The fine focussing is
obtained by screwing it up or down over a short distance along that
arm. It differs from the modern type in that it can be revolved, together
with the arm and the stage round the optical axis, a possibility of mo-
tion shown in a great many instruments dating from the middle of the
19th century; it was meant to facilitate the modification of the direc-
tion of the light-rays relatively to the object while working with a
slanting illumination. The stage is a mechanical one after the (slightly
altered) Tyrrell system. Underneath this stage a short tube adjusta-
ble by rack and pinion, carries at its lower end a diaphragm wheel
with four apertures, while at the same time its upper end can be cove-
red by perforated caps. The microscope tube is extensible. The optical
parts accompanying the instrument are 6 objectives and 3 eyepieces.
In the latter is a groove in which a micrometer can be fitted. The
following magnifications were measured by Harting. The resolving
powers here given are for the weakest eye-piece and with tube pushed
in- The values for the other eye-pieces do not differ materially from
these:

drawing prism of Chevalier
eyepiece micrometer divided in 0.1 mm
object micrometer divided in 001 mm.

In the middle of the 19th century the firm Lerebours, later on
Lerebours et Secretan, became very well known for their construction
of achromatic microscopes.

It is screwed on its own box when in use and the stage and the
illuminating-mirror can slide along the stand by means of rack and
pinion (fig. 33). An extra arrangement for fine focussing is attached

to the stage. The latter consists, namely, of two plates, one over the
other, of which the top one can be screwed up and down relatively
to the lower one. On this stage can be fitted another, with centring
adjustment (Oberhäuser system, Harting III pg. 376 and pi. IX fig.
12). Under the stage is a diaphragm wheel with four apertures.

a)nbsp;as a horizontal microscope, with the aid of a prism and objective
fitted together in a mount, attachable to the instrument by a bayo-
net socket;

b)nbsp;as a vertical microscope, with the aid of a mounted objective,
without a prism, but likewise attachable by a bayonet fitting.

The microscope tube is extensible. There are three objectives with
this instrument. No. 1. is a single achromatic lens. No. 2. and No. 3,
each consist of a system of three lenses. There are also 4 eyepieces
of which No 2. is equipped with a point micrometer. In order, name-
ly, to determine the distance between a pair of points in the image,
this eye-piece is fitted with two minute sharp-pointed shafts, which,'
by screwing them in or out, can be adjusted in such a way that their
ends coincide with these points. The required distance can then be
measured subsequently by means of the objective-micrometer.
The magnifications with tube pushed in are:

Further accessories with the instrument are:
small trough for liquids
cajnera lucida of Machet

The box, however, belonging to it is inscribed: quot;Secretan, succes-
seurquot;.

The microscope is of the same design as the quot;drumquot; microscope
reintroduced by Oberhäuser about the year 1835. The base has
the form of a drum and the illuminating mirror is fitted inside it. The
stage is mounted on top of it and under the stage is a wheel of dia-
phragms with 5 apertures. Above the stage is a fixed tube, the inside
of which is threaded with a very coarsely worked pitch with a high
speed and in which the microscope tube, by turning it on its axis, can
be screv/ed up and down. The fixed tube carries a condensing lens for
opaque objects. The mounting of the objective is very remarkable.
The mount consists of two cones, one inside the other, to each of
which the various small lenses can be screwed on. This device
made combinations of the lenses possible in which they are not
screwed one right against the other but remain apart at fixed distances
one above the other. According to Harting three lenses belonged to
this instrument (Harting III pg. 198 and pi. V fig. 8'), which could
be combined in the following way:

Unfortunately lens 1 is missing, and it was therefore impossible to
measure any of these combinations.

When the instrument is used in the ordinary way the magnifica-
tions and resolving powers are:

A very great improvement in the construction of microscopes is
due to G. Oberhäuser in Paris, (who was afterwards succeeded by
his nephew E. Hartnack, at first also in Paris, later after 1870,
in Potsdam). In 1835 Oberhäuser had already succesfully reintro-
duced the so-called quot;drum-microscopequot;. In 1848 however, he designed
and made the first horse-shoe microscope, a form which has held its
own up to now.

Though it does not bear his signature, this instrument is very pro-
bably made by Oberhäuser. The construction answers completely to
the description by

As the name indicates, the base is drum-shaped; an opening is made
in it to allow the light to fall on to the illuminating-mirror inside the
drum, (fig. 34). The stage is mounted on it in such a way that it
can be turned, together with the microscope itself, round the optical
axis. Underneath the stage is a slide in which a short tube can be
moved up and down with the aid of a lever. In this tube the following
articles are made to fit:

c.nbsp;an apparatus after Nachet for slanting illumination (Cp.
Harting III pg. 352, pi. VI fig. 9.)

d.nbsp;a small tube into which one of the objectives can be
screwed so as to serve as a condensing-lens.

The coarse adjustment is obtained by rack and pinion; the subse-
quent fine adjustment by means of a screw.

therefore, as an erecting and as a pancratic microscope. The second
objective furnishes, namely, an inverted image of the image, due to
the first objective, which is itself already inverted. In this way, the
image is not only put right again, but the arrangement admits of a
continuous alteration of the magnifications, too, by changing the
distance between the two objectives. (Cp. Harting III pg. 262).

6 objectives, each consisting of three lenses
one objective, Nachet No 7.
three eyepieces, numbered 1, 2, 3

one eyepiece of the same power as No. 1 but provided with
a micrometer with divisions of 0.01 mm-

The resolving power turns out to depend on the objectives only;
the eyepieces have no influence. The images are slightly distorted,
even in the case of smaller magnifications.
Still further accessories are:

mounted analysing calcite prism to be fitted on the eyepiece
mounted achromatic calcite prism
camera lucida of Nachet
various dissecting implements
3 object micrometers signed

quot;Charles Chevalier. Palais Royal a Paris,quot;
One of them is divided in squares of ^/loo another in

This instrument is signed quot;Georges Oberhäuserquot;. In the micro-
scope-tube the number 1550 is engraved, (cp. Harting III pg. 290). In
1848 the Physical Laboratory bought it for ƒ 350. Later on it was

given to Harting in loan. It was evidently he who ordered it for the
laboratory, for the case accompanying it contains a letter to Harting
written by Oberhaser and dated Sept. 21st 1848.

The original illuminating mirror and the diaphragm apparatus are
removed and replaced by an illuminating arrangement of Harting's
own invention. The mirror is fixed to a set of hinges which admits
of its position out of the optical axis for slanting illumination- The
illuminating-set itself can be slid by rack and pinion along the divi-
sions of a scale so that its displacements can be measured. It consists
of a plano-convex condensing lens of focal lenght 1.5 cm. and under

it a square diaphragm of which the size can be varied gradually.
(Diaphragm of Dollond. Cp. Harting III pg. 363 and pi. VII fig. 15
and 16). The whole arrangement can be moved on a slide-rest out
of the optical axis and can also be inclined in such a way that the
light can always pass at right angles through the condenser. Another
slide-rest is attached underneath to the bottom of the stage, which
can be made to carry small tubes fitted with diaphragms. For a de-
scription of this illuminating arrangement see:
Harting I. pg. 285—287.
Petri, pg. 220—221.

The coarse adjustment is obtained by moving the microscope tube
up or down by hand, the fine focussing, however, by means of a
micrometer-screw in the head of which is a scale divided into hundred
parts (one revolution of the screw = 0.492 mm). The microscope-
tube is extensible and the extensible part is also provided with a
scale. The tube, together with the stage, of this instrument can ti;rn
round the optical axis.

Of all the original accessories, only two small achromatic lenses
and 5 eyepieces are left. Of the latter those numbered 1 and 2 have
equal powers, but 2 is fitted with a micrometer with a scale division
of 0.01 mm.

With the instrument is a very extensive table, drawn up by Harting,
of magnifications obtainable with this microscope, with the aid of
many objectives and eyepieces belonging to other instruments.

arrangement, as well as its optical qualities, nearly reach the high
standard of modern microscopes. It is mounted on a horse-shoe base
by a joint, so that it can incline at any angle desired. To the bottom
of the stage is attached a heavy brass strip, in the slot of which the
illuminating mirror and the plano-convex condensing lens can slidi
up and down. The mirror admits of a sideways motion, too, to make
slanting illumination possible. The condensing lens can be fitted with
diaphragms which screen off the centre of the field of vision, (dark-
ground illumination). A slide rest, carrying a diaphragm-holder, is
attached underneath the stage. The diaphragms belonging to it are
separate small caps. This holder can also be fitted with a slide for
small blue glasses. The microscope itself, together with the stage
can be turned round the optical axis. The coarse focussing is effected
by rack and pinion and the finer adjustment by means of a micrometer
screw.

There are 6 objectives with the instrument, marked 2, 4, 5, 7, 8
and 9, and one water-immersion, marked 11. The numbers 9 and 11
arc fitted with cover-glass correction. There are, moreover, 7 eye-
pieces: 1, 2, (fitted with a 0,1 mm. micrometer) 3, 4, 5, 5' i) and 6.
The last one is quot;holostericquot;, that is to say, a Huyghenian eyepiece,
consisting of a single sohd piece of glass with ground surfaces of
different curvature on both sides. With the microscope is a table of
magnifications, obtainable with objectives 2, 4, 5, 7 and 9; and with
eyepieces 1, 2, 3, 4, 5, provided by the maker himself. Objective 8,
the immersion 11, and the eyepieces 5' and 6 were evidently bought
and added later.

To the microscope belongs, further, a very lage plano-convex
illuminating lens mounted on a separate foot.

The very large magnifications with objective 9 are evidently ob-
tained at the cost of the resolving powers.

As regards the latter, the instrument can certainly compete with
many modern microscopes. One of the modern instruments, con-
structed by one of the best factories, gave, with the same magnifi-
cations, the same values for the resolving powers. And for the smaller
magnifications the maximum resolution obtainable without the help
of some special device, is reached-

The firm, Nachet in Paris, which still exists, became very well-
known in the 19th century for its microscopes. The Utrecht collection
possesses only three smaller instruments of this make.

Its construction is very simple. The hollow illuminating mirror is
fitted in the interior of the drum-shaped base. Underneath the stage
is a revolving diaphragm-wheel with four apertures, and above the
stage there is a separate plate which can be screwed up and down,
a contrivance by which the fine focussing is obtained. The coarse
adjustment is obtained by moving the microscope tube up or down
by hand. A plano-convex illuminating lens is hinged on to the body-
tube in which the microscope can be made to slide. The microscope
tube itself is extensible.

Its accessories are, at present, only one eyepiece and three objec-
tives; two of the latter consist of two, and the third of three small
achromatic lenses.

Its accessories are two eyepieces, marked 1 and 2, and further
one objective consisting of two systems of lenses about 1.5 cm apart.

Although, like the other instruments of Nachet. it is mounted on a
round foot, the drum is dispensed with. This made it possible to fit
the mirror so as to admit of motion in all directions. Under the stage
is the diaphragm-wheel with three apertures. The coarse adjustment
is again effected by hand; the fine one. however, by screwing the
microscope up and down. An illuminating lens belongs also to the
instrument. The optical parts are: three objectives marked 1. 3 and 5
and two eyepieces 1 and 3. Objective No. 1 consists, like the one under
R. 1. of two lenses 1.5 cm apart. Numbers 3 and 5 consist of three
small lenses screwed one immediately on top of the other. Eyepiece
No. 3 contains a micrometer in 0.1 mm.

It is constructed as follows: on a rectangular foot are mounted two
brass pillars which carry the stage and the microscope. The latter is
attached in such a way as to admit of every requisite inclination. Un-
der the stage are the mirror and diaphragm wheel with four apertures.
Above the stage a harp-shaped object-clamp can be slid up and down
with a sleeve along the tube carrying the microscope. The coarse fo-
cussing is done by hand, the fine one by means of a screw. With the
instrument are one objective, consisting of two small lenses, and one
eyepiece. The magnification, with tube pushed in, is X 250, with tube
drawn out, X 320; the resolving powers in both cases are V400

This instrument, ^oo, admits of every requisite inclination between
two pillars which here, however, are mounted on a horse-shoe foot. The
stage, under which a diaphragm-wheel with four apertures is fitted,
admits of motion in all directions, by means of a lever -) (fig. 35).
The prelimanary focussing is effected by rack and pinion; the final
one by means of a screw, which moves the objective up or down
with the aid of a lever system. A condensing lens it attached to the
stage. The optical outfit accompanying the instrument consists of 3
objectives and 2 eyepieces. The objectives are numbered 1, 3 and 4.
No 1. is a system of 2 achromatic lenses No. 3 and 4 are systems of
3 small achromatic lenses.

M Schokking. formerly living in Binnen Wicringerstraat, Amsterdam, lived in
1875 at Spui 13, also Amsterdam. The number 18 was altered in 1884 to number
32. The microscope must therefore be dated sometime between 1875 and 1884.
2) More or less as illustrated in Harting III pi. VIII fig. 15.

This instrument is fastened by means of a joint to a tripod of a
peculiar shape. ^) The stage is a mechanical one after the Tyrrcl
:^.ystem (slightly altered) on top of which a revolving stage is fitted. TJie

The tripod is cxactly the same as the one in Petri pg. 216 where a microscopc
of Mawson and Swan is illustrated.

coarse focussing is again done by rack and pinion, the final adjiistment
by rrjoving the objective up or down by means of a screw. The op-
tical parts with the instrument are of Nachet's make and consist of two
objectives, and one eyepiece. The two objectives are Nachet No 2
and No 5. The latter is fitted with a correction for cover-glaiss thick-
ness. The magnifications and resolving powers are:

Here the course focussing is again done by hand; the fine one
however, by screwing the stage up or down. Accompanying the in-
strument there are two eyepieces and four objective lenses marked
1—4. Only the sets 1, 2, 3 and 2, 3, 4 give images of fairly good
quality. The images of other combinations or of the lenses used
separately, are rather poor. These two combinations were evidently
the only ones intended to be used.

It was made by him especially for a prize competition at Leiden
where it won the gold medal. Hence the engraving in the foot: Gold
medal. Leiden. 1865.

Zaalberg van Zelst was established as an instrument maker at Singel,
Amsterdam at about 1860. He subsequently carried on the same profession at
The Hague.

the stage, the illuminating mirror, a condensing lens, a piece of blue
glass and a continuously variable diaphragm, system Dollond (cp-
Q. 2.). The condenser is fitted with a diaphragm for dark-ground
illumination and both condenser and blue glass can be turned out
of the optical axis. On the stage a movable slide serves to place the
object glasses against it- The coarse focussing is done by hand, the
fine one by means of a screw. Another illuminating lens of dark blue
glass is attached to the microscope. Accompanying the instrument is
a small case made in imitation of a miniature prayer-book and con-
taining four objectives and three eyepieves. The objectives are num-
bered 0, 1, 3 and 5. The following magnifications and resolving
powers were measured:

There is a table of magnifications on a paper, pasted in the lid.
These values are however, from 50% to 75% too high.

The height of this diminutive drum-microscope measures only 8cm.
On the lid of the case there is a groove in which the instrument can
be set up. Its magnification is X 45 and the resolving power ^hoo
The images are distorted and still slightly chromatic.

For dissecting microscopes, use is made of low power simple or
compound microscopes, but compound microscopes with negative
eyepieces, because the images of these microscopes are not inverted.

On a heavy foot a tube is mounted to which the large stage is
attached. The latter is fitted with hand-rests. A triangular rod can
be slid up and down in the tube by rack and pinion. This rod carries
the small microscope. Under the stage the illuminating mirror is
jointed so as to admit of a motion in all directions. The eyepiece is
a very strong, small negative lens. The objective consists of three
achromatic lenses which can be used either separately or combined
in a set of two, or all three together. The magnifications and resolving
powers obtained are:

Since the higher the magnification, the stronger the illumination of
the objcct must be in order to obtain images of the right intensity,
and particularly so when the image is projected on a screen, it is
only natural that during the 18th century one availed oneself for
micro-projection of the only strong source of light then at one's dis-
posal, namely the sun. As however the direction observer-sun changes
continually, it was necessary to fit the microscope with an adjustable
mirror, which could be turned so as to follow the motion of the sun.
As a rule, the solar mirrors could move in two independent ways,
namely round the optical axis of the microscope and round an axis
at right angles to the first. The latter rotation, therefore, varies the
inclination of the mirror. By means of these tv/o rotations one could
always contrive to throw the light of the sun through the illuminating
tube.

The inclination of the solar mirror of this very primitive instrument
i.', varied with the aid of a nut which can turn in the plate carrying
the mirror and the microscope; and through the nut passes a screw,
v/hich is simply bent round, and which is attached to the mirror by
a joint. (Fig. 36). The motion round the optical axis is effected by
turning the instrument wholesale round it. The projecting lens is
screwed on to the front end of the microscope tube, while the further
end is fitted with a condensing lens. The object is held firmly, as
in the case of the screw barrel microscopes, between two small brass
plates; these are pushed by a spring against a ring scrcwn round the
microscope tube. By screwing this ring backwards or forwards, the
object moves relatively to the projecting lens and this is, therefore,
the way, focussing is effected. With the instrument are 4 small pro-
jecting lenses. Considering the rather poor workmanship of the me-
chanical parts these lenses are very satisfactory. The magnifications
(for 25 cm distance) and the resolving powers are namely:

This instrument belonged originally to the foundation quot;van Rens-
woudequot; and is therefore probably the work of one of its wards. Its
arrangement is very much the same as that of U. 1, only the inclination
is varied here by a straight screw of which the motion is transferred
to the mirror by means of a lever system.

With the instrument are 2 projection lenses with magnifications
of X 7}/^ and X 17. The latter lens is able already to resolve i/ioo

Of this instrument, which is contained in a little mahogany chest
with two drawers, the solar mirror is missing. The arrangement agrees
completely with the one described and illustrated in Adams pg.
113—115, resp. pi. VI.

To the front end of the microscope tube, which itself is fitted with
two condensing lenses about 11 cm apart, a narrow tube is attached
which contains the Hartsoeker-Wilson object-carrier. Over this tube

another can move by rack and pinion. In the front end of the latter
a slide with six different projection lenses can move to and fro.

This instrument can be used either as a hand-microscope or as
a projection-microscope. As a hand-microscope it is completely similar
to the screw-barrel microscopes after Hartsoeker-Wilson. described
under C. In order to use it as a projection microscope the condensing
lens is removed and the microscope is put over the conical end of
a tube, containing its own condenser, to which the solar mirror is
attached. The microscope is quite complete with object- and lens-
holders for opaque objects, little glass tubes etc. Everything is kept
in a small box. Its optical outfit consists of

and a description of these objects in Enghsh, which suggests that the
origin of the instrument might be EngHsh.

This instrument hke the one described under G. 4, is made almost
entirely of wood and cardboard, (fig. 37). The object is pressed
tight against the edge of the microscope tube by means of a spring.
The focussing is effected by screwing the projection lens in its woo-
den mounting backwards or forwards. From the description accom-
panying the instrument we gather that it was constructed by the
quot;Feld-prediger der hochloeblicher van Kalksteinischen Regimentsquot;.
(Field chaplain to the Kalkstein regiment) Junker at Magdeburg. In
this description which is dated 1791 Junker explains at some length
how the microscope can be used as either a solar microscope, as a
simple microscope or as a camera obscura.

As its magnification he gives X 4096, resp. X 32768! Only one lens
with magnification 32 and resolving power i/joo mm is with the in-
strument. Junker gave evidently the linear magnifications to the third
power (4096 = 16^ and 32768 = 32^), as wrs often done in those
days in order to make it seem very strong.

quot;Dieses ganzes Instrument nun erbiete ich mich den Schulen und
„Erziehungsanstalten für 5 Rthr im Golde, andern Liebhabern für 6
,,Rthr im Golde besorgen zu lasfcn, wenn es bei Zeiten bei mir bestellt
,,und das Geld darauf voraus bezahlt wird weil ich sonst nicht immer

„im Stande bin, den groszen Kostenaufwand, den dieses Unternehmen
„veranlasst, zu bestreiten. Wer weiss, dass ein englisches Sonnen-
„microscoop 50 bis 100 Thaler kostet, und es gesehen hat. dass ein
„solches Instrument, obgleich gans aus Messing gearbeitet, nichts mehr
„leistet, als das, was ich anbiete, der wundert sich, wie es moeglich
„sey, es um einen so geringen Preis zu verschaffen. Da es mir aber
,.nicht um Gewinn, sondern um Ausbreitung wohltätiger Erkenntniss
„der Werke Gottes zu thun ist, so uebernehme ich freilich manche
„damit verbundene Mühe und Arbeit selbst, ohne auf deren Belohnung
„zu rechnen. Ich opfere gern meine Nebenstunden auf, und wage an-
„sehnliche Kosten, wenn ich nur meinen Zweck, dies interessante und
,,wohlthätige Instrument in mehrere Hände zu bringen, erreiche. Be-
„sonders wünsche ich es in den Schulen und unter dem Mittelstände
..bekannter zu machen, weil bis jetzt hieher dergleichen microscopische
„Kenntnisse, wegen des Preises der Instrumente, nicht häufig gekom-
,,men sind. Ich habe oft gehört, dass selbst gebildetere Menschen
„Erzählungen von manchen Erscheinungen durch das Sonncnmicros-
,,coop für blosse Fabeln gehalten haben, weil ihnen dergleichen noch
,,nicht einmal zu Ohren, geschweige denn vors Auge gekommen war.

,,Setzen mich daher mehrere Bestellungen dazu in den Stand, so will
,,ich von dem etwaigen Ueberschusse mehreren Schulen und unbemit-
,,telten Familien das Instrument theils schenken, theils um einen noch
..wohlfeilem Preis ueberlassen.

„Ich wünsche von Herzen dass meine wohlgemeinte Absicht nicht
,,ohne Segen sey, und dass Viele durch dieselben in den Stand ge-
,.setzt werden mögen, Gottes Grösse auch in den kleinsten seiner
,,Werke näher kennen zu lernen.quot;

Finally the quot;Prediger Friesch zu Xanten im Clevlschenquot; is mentio-
ned in a margin as the agent quot;für die Holländische Gegende.quot;

The microscope was bequeathed by Pro/. Dr. G. Moll together
with a great many instruments to the Physical Laboratory.

This instrument bears the signature: quot;J. Cuthberson te Amster-
damquot;^). It is large and its mechanical parts are of splendid work-
manship. The very large solar mirror is fastened to the cone-shaped
illumination tube in a very elegant and solid way. Both ends of this

C.ufhhcrson was an English instrumcn: maker; he was established in Amsterdam
at about 1780. He became known especially for designing and constructing numerous
elcctrica! apparatus. His most famous piece of work is the huge electrical machine
made for M. van Mantm in 1784, which is still to be seen in the hall of Tcylcr's
Museum at Haarlem. The Physical Laboratory at Utrecht possesses also a machine
made by him; though it is much smaller than the one at Haarlem it exceeds an
average human being in height. During the occupation by the French, Cuthberson
left Holland and settled in London.

illumination tube are fitted with a condensing lens, the wide end
with a large low power lens, the narrow end with a small high power
one. In order to make the concentration of light on the object possible
the latter lens can be moved by rack and pinion. There are two diffe-
rent mounts for this lens, each with its own rack. They are meant to
be used with the two different object-holders belonging to the instru-
ment. At the front end of the illumination tube, namely, a rod is at-
tached, likewise capable of rack and pinion motion and carrying a large
object-holder to which the wooden slides with rather big objects can
be fitted. To this large object-holder a smaller one can be screwed
on to hold the usual objects mounted in small bone sliders. To both
object-holders there belongs a sharp-pointed shaft with forceps, which
by means of a ball and socket joint can move in every direction. The
projectionlens, which for focussing can be moved by rack and pinion
also, is placed in front of these object-holders- With the instrument
are 6 projection lenses with the following magnifications and resolving
powers:

The strongest projecting lens is mounted in such a way that it could
not very well be cleaned; its resolving power, here given, is therefore
only a lower limit. As a detail characteristic for the period in which
the instrument was used it is worth mentioning that one of the obje^'ts
in the wooden slide is replaced by an ordinary piece of glass bearing
the inscription:

The instrument was bought by the Physical Society at Utrecht,
towards the end of the 18th century.

used for the microprojection of horizontally placed objects. The cone-
shaped illumination tube carries at one end an interchangeable con-
densing lens, and to the same end is attached the solar mirror- The
other end fits in a brass box in which a mirror reflects the light, hori-
zontally incident through the illumination tube, in a vertical direction.
Underneath the mirror is the object-holder and still lower down a
revolving wheel admitting of rack and pinion motion and fitted with
four projecting lenses of various powers (resp. magnifications of
4, 5, 9 and 13). After passing through the projecting lens, the light
is once more made horizontal by a second mirror of which the incli-
nation can be varied by a screw.

In the foreground are shown the various accessories necessary for
other purposes. To the left is the apparatus for the projection of opaque
objects. One end of a brass tube is closed by a small pane of ground

glass, the other end by a hollow mirror with a hole in the centre.
Close to the focus of the mirror the object is placed, fixed in an ivory
cap which is clamped in a brass ring. Behind the hollow mirror another
brass ring, carrying the projecting lens is fitted so as to allow of
a backward and forward motion. The light falling through the small
pane of ground glass is concentrated by the hollow mirror on the
opaque object and passes subsequently through the opening in the
mirror on to the projecting lens. With this apparatus are 4 projecting
lenses with magnifications of IJ^. 4 and 6.

The arrangement shown in the centre foreground is used in the
case of a transparant object, which is clamped between two little

brass plates in a slide; in front of it is fitted a wheel with four pro-
jecting lenses (magnifications 3, 5, 13 and 17 diameters); the strongest
lens resolves ^/joo The focussing is again effected by rack and
pinion. Besides these lenses the four lenses of the apparatus for
opaque objects can be used for transparent objects by screwing them
on to a ring fitted especially for this purpose in front of the revolver.

Finally, to the right, the arrangement is shown for projecting ordi-
nary lantern plates. For this purpose, the illumination cone is remo-
ved wholesale, and the projection apparatus is screwed on, by means
of a brass ring, to the plate carrying the solar mirror.

This instrument is signed quot;Dollond. Londonquot;. It is a beautifully-
and well-made projection-microscope, bought by the Physical Labo-
ratory in 1830 for ƒ 504.

It is almost entirely similar to the instrument, described and illus-
strated in Adams, pages 106—113; resp. plate V (See fig. 39).
The optical arrangement is as follows: the illuminating mirror is
attached to a heavy brass plate fitted with a condensing lens. This
plate carries the illumination-cone at its other side. The projecting-
cpparatus for either the transparent or the opaque objects can be
screwed on to the front part of this illumination tube. The first is a
brass tube containing a spring object-holder; a second tube fitted with

the projecting-lens at its front end can shde by rack and pinion over
the first one. For projecting lenses there are with the instrument:

A special slide fitted with a condensing lens and inserted in the
spring object-holder immediately in front of the object, belongs to
each of the projecting lenses.

The projecting apparatus for opaque objects consists of a rectangu-
lar brass box containing a plane mirror which can be inclined in such a
way, by means of a screw, that the sunlight is concentrated on the slide
with opaque objects, which is clamped in the spring object holder.
Opposite this slide two different tubes can be stuck into the box each
containing a system of two lenses with variable distance. When at
minimum distance the magnifications are resp. X 2 and X 8. With
the instrument are. apart from a live box, a great number of slides
for all kinds of transparent and opaque objects.

When once light sources of sufficient intensity could be obtained
so that sunlight could be dispensed with, the construction of project-
ion microscopes without solar mirrors was started. In the second half
of the 18th century and the beginning of the 19th, the Argand lamp
was very popular. This was an oil lamp of which the light intensity
was increased by a suitable supply of air. Later on came gaslight,
then lime light and finally, electric light.

This extremely beautiful and complete instrument is made by J. H.
Onderdewijngaart Canzius^) at Delft. At the Exhibition of National
Industry held at Utrecht in 1808, where the maker was awarded the
honorary prize in gold, the microscope was bought by order of King
Louis Napoleon and subsequently offered by him to the Theatrum
Physicum. It differs greatly in construction from the instruments de-
scribed above. (See fig. 40). To a heavy tripod is attached a horizontal
pyramidal mahogany box carrying at its one end the projecting
system and at the other a plate of ground glass as a projection screen.
Immediately in front of the screen a large converging lens can be
placed. This lens forms an image of the projecting system in an eye-
ring which, fastened to a brass arm, protudes from the microscope.

1) J. H. Onderdewijngaart Canzius was born in 1771 at Delft of well to do
parents. He studied law and physics at Leiden and took his law degree in 1790.
In 1792 he established himself as a solicitor and notary public but owing to the
revolution of 1795 he had to give up these functions. He then founded a workshop
for the making of instruments at Delft, which under the patronage of the King
flourished. But after the departure of His Majesty in 1810, business slackened
owing to the general depression. Canzius left the country and settled down in
Emmerich where he was appointed professor of experimental physics and, shortly
after, burgomaster. After Germany's liberation from the French occupation he was
offered a position at the High Court of Justice in Berlin but did not accept it. In
1816 he returned to Holland where he held various important government posts.
In 1826 he became Director of the National Museum of Art and Industry at Brus-
sels but had to resign owing to the separation of Belgium from Holland. He refused
a Professorship at the Université Libre at Brussels because he declined to become
naturalized as a Belgian. He returned to Delft where he died in 1838. He was not
only interested in law and physics but also in theology. For many years he was
leader of the congregation quot;Christo Sacrumquot; at Delft. In 1811 he was made hono-
rary doctor of letters at the University of Harderwijk.

Therefore when the eye looks through this opening all the light that,
after passing through the projecting lens, goes to form the image, will
be directed by the large lens to the eye, thus making it possible to
really observe images of high intensity. Under the mahogany case a
tube is attached of square cross section in which by rack and pinion
a square rod can move. To this rod the object-holder is attached.
There are two different object-holders with this instrument:

a) for opaque objects: a semi-spherical condenser and an inclined
hollow mirror concentrate the light on the object, fastened on a woo-
den slide which can be clamped above the illuminating system.

b) for transparent objects: a brass tube contains at one end a spring
object-holder, at the other end a condenser consisting of two plano-
convex lenses. If desired, a ring, adjustable by rack and pinion, can
be attached to the object-holder; in this rimj the lov/ power pro-
jecting objectives c.q. a compound microscope can be fitted.

one projecting lens with lieberkuehn: magnification: X 2
two doublets: magnifications: X 9 and X UM
seven small projecting lenses: magnifications: X 4. 53^2' 6.
91/2. 11 and 17.

All magnifications are determined for 25 cm. distance. Since, how-
ever, the lantern is 45 cm. long, the above values must, for this instru-
ment, be multiplied by ''/r,. Not one of the lenses is capable of
resolving only ^/joo

berkuehn mirror. It has 6 objectives, the lens of number 4 however
is missing. The various magnifications and resolving powers are:

With the instrument is a mahogany box containing many objects
and accessories. The inventory of the objects is in English, so they
were evidently supplied by an English tradesman.

It is comparatively heavily built and was purchased about 1830
together with two gas tanks, by the Physical Society at Utrecht. A zinc
lantern placed on a little shelf contains the oxyhydrogen burner.
(Fig. 41). To the front of the lantern is attached a bent tube fitted
with a condenser, consisting of two bi-convex lenses, and with a
plane mirror. The end of this tube contains the spring object holder
and also the projecting doublet consisting of two plano-convex lenses
with their flat surfaces turned towards the object. The focussing
is effected by moving this doublet by hand. Its magnification is X 7.

It was purchased in 1852 by the Physical Society at Utrecht for
ƒ 55. It is meant to be used in combination with a projecting lantern
and has, therefore, no solar mirror. Inside the illumination tube, which
consists of separate telescoping parts, a fixed condenser is fitted
on the side of the lamp; on the side of the object, however, is a con-
denser which can move by rack and pinion. In front of the tube the

object-holder is attached, consisting of two plates, clamped together
by a spring. To this object-holder a rod is fixed along which the
projecting-system can slide by rack and pinion, and there is also a

screw for sharp focussing. A diaphragm is attached to the front end
of the rod to screen off any diffused light

The projecting system consists of three small achromatic lenses,
all alike, each of which, separately, gives a magnification of 9, two
together of 17 and all three combined of 24. This last combination
can resolve Vioo mm.

Moreover, to the front end of the lens-holder a strong negative
eye-piece can be fitted, making it possible to use this system for
dissecting purposes.

A preparation of a vegetable epidermis, probably of a stem, is fixed
between 2 small glass plates in an ivory mount. On the mount is
inscribed:

This preparation shows indeed a very regular structure and can
be used quite well as a micrometer. The average distance between the
stripes turns out to be 0.035 mm, corresponding with 65 divisions per
Paris line. On the little box of palmwood is written: quot;Micrometre pour
M. le professeur Rossyn i)quot;

It was very probably bought by the Theatrum Physicum about the
end of the 18th century.

A small box of palmwood contains two micrometers cut in glass.
One is divided in squares with sides averaging 1.111 mm and 0.222
mm; the other in squares with average sides of 1.123 mm and 0.225
mm and in rectangles of 1.123 X 0.225 mm^ (Cp. Harting III
pg. 409).

On the lid of this box is inscribed quot;Micrometers van Branderquot;,
They were bought by the Physical Society at Utrecht at the end of
the 18th century.

This case contains four glass micrometers mounted in brass and
also two ivory micrometers. The Physical Society at Utrecht pur-
chased it for ƒ 25 from Newman in London at the beginning of the
19th century. Each of the ivory micrometers has two mutually perpen-
dicular sets of parallel lines, resp. Vioo inch and Vso «nch, apart,
which by their intersection form squares of these dimensions.

1) Prof. /. P. F. Rossijn was from 1776 to 1812 director of the Theatrum Physicum
of the Utrecht University.

The glass micrometers have also two mutually perpendicular pa-
rallel divisions of resp. Viooo. Vsoo- Vioo and v50 inch.

It is mounted in brass and consists of the photographic reproduc-
tion of divisions reduced to a very small scale. One division corres-
ponds to 0.059 mm.

In 1846 the Physical Society at Utrecht bought, for ƒ 12.50 a case
containing two test-plates. At present only one is left, which is signed:

This plate which is intended to be used for the determination of the
resolving power of a microscope by the direct method, has 10 groups
of equidistant lines- The mutual distances in the various groups are,
according to Harting's measurements:

Elaborate discussions on the Nobert testplates are to be found in
Harting III pg. 412—414.

The plate itself is of realgar in which 12 groups of parallel lines
are cut. Their various distances are:

A telescopic tube is fixed in a table-clamp. Fitted at the upper end
of the tube is a small drawing prism which can be placed over the
eye-piece of the microscope. Two small lenses (one concave and the
other convex) and a diaphragm are hinged on to the prism. The
whole of it is contained in a morocco leather case together with the
instructions for use, mentioning the following firms as makers of this
kind of instrument:

This instrument was bought from Dollond by the Physical Labo-
ratory at the beginning of the 19th century.

On to the mount of the prism two dark coloured pieces of glass and
a convex lens hkewise of dark glass are hinged. It is a very thorough-
ly finished piece of workmanship and was bought by the Physical

It is a more modern make of camera lucida: the adjustment in
height is effected by rack and pinion. With the instrument are 10
small lenses of various powers, which can be inserted in the mount
of the prism,

This instrument was probably made by Zeiss about 1880. It consists
of a tube, bent into 2 arms at right angles to each other, which con-
tains a reflecting prism. All of it is fitted, instead of the eyepiece,
on to the microscope. At the horizontal end is an eyepiece and behind
this is a small rectangular prism with a diaphragm. A description of
this type of instrument is to be found in: van Heurck pg. 89.

It is fitted with the illuminating apparatus after Harting as descri-
bed under Q. 2.

An oak chest with 9 drawers containing many objects, a number
of which are mounted in bone, others on cards.

This is a very beautifully finished chest with shutter-fastening,
containing many objects and dissecting accessories.

J. J. van Drccven was amanuensis at the Physical Laboratory at Utrecht. Before
then he was established as an instrumentmaker at Nijmegen.

This collection consists of a few hundred prepared objects mounted
in slides of wood or bone, in ivory caps or on small circles of card-
board.

These are two gas lamps surrounded by metal cylinders with a
few openings in them. Glass rods bent to a suitable shape can be
fitted with one end in these openings so that the other end reaches
underneath the stage of the microscope. The light of the lamp is
then forced by total reflection to follow the glass rod and is by this
means thrown on to object. The lamps are signed:

On a round brass foot is mounted a small carbon resistance and
an arm; the latter is movable in all directions by means of a ball
socket joint. It carries at its extremity a small electric lamp consisting
simply of a small glass bead, in which a filament of platina is melted.

Lens	Magn. p.	Res. p.
1	X 400	Vgoo mm
2	160	V400 quot; quot;
3	100	1/400 quot;
4	57	200 quot; ••
5	26	Vioo quot;
6	16	V100 quot;

1	Lens	-------	Magn. p.	Res. p.
	1		X 120	1/400 mm
	2		80	200 quot; ••
	3		50	V200 •• quot;
	4		40	V200 quot; quot;
	5		25	V100 •• ••

Magn. p.	Res. p.
X 16	_
20	i/ioo mm
30	1/100 quot; ••
40	V200 •• quot;
60	igt;00 •• quot;

Magn, p.	Res. p.
X 50	1/200 mm
32	200 quot; quot;
28	200 quot; quot;
21	Vioo ....
20	Vioo ..
19	1/100 quot; quot;
10 8	—

Obj:	Magn. p.	Res. p.
1	X 275	i/oQo mm
2	100	1/100 quot; quot;
3	80	100 quot; quot;
4	60	100 quot; quot;
5	28	100 quot; quot;

) / '100	20	20	35	35	—	—	11
1/ '200	40	40	85	60	—	IV	22
V4OO	100	120	250	120	75	45	44
'/coo	200	—	—	220	115	70	67
'/BOO	i 360	—	—	—	165	100	89
1/ '1000	—	—	—	—	225	135	111
1 / / 1 200	—	—	—	—	295	175	133
Vl 400	—	—	—	—	395	235	156
'/\| COO	—	—			—	360	178
''1800	-						200

Obj.	Magn. p.	Res. p.
1	X 200	1/200 mm
2	75	Vioo ....
3	55	ICQ quot;
4	25	Vloo ...
5	15	—

Obj	1 j Magn, p.	Res. p.
1	X 180	1/200
2	280	Vioo ....
3	58	Vioo ....
4	42	Vioo ....
5	32	Vioo ....

Oc.	R.	Ro	n	f
I	6.2 cm	4.5 cm	1.5	5 cm
II	6.2 „	7.0 „	1.6	5.2 „
III	4.2 „	4.2 ,.	1.5	4.2
IV	6.2 ..	6.2 ..	17	4.5 „

Obj-	Magn. p.	Res. p.
L	X 120	i/.joo mm
L 1	145	V200 .. ..
L 2	135	V200 .. ..
L 3	130	V200 .. ..
1	46	V100 .. ..
1 2	78	V100 quot; quot;
1 2 3	92	V20() •gt;
2	27	—.
2 3	52	100 quot; quot;
3	17	—

j magnif.		resolving p.	field of view.
a. with the between-lens
tube pushed in tube drawn out	X 47 85	Vioo nim 100 quot; ..	234 mm 2 ., „
b. without the between-lens
tube pushed in tube drawn out	X 65 90	Vioo nim Vioo .. ..	1% mm iH ....

Obj.	Eye p.	Magn. p. tube pushed in	Magn. p. tube drawn out	Resolv. p.
1	1	X 100	X 175	V'-'OO nim
1	2	85	150	V200 gt;• ••
2	I	60	120	V200 .. ..
2	2	50	95	Vioo gt;• M

Obj.	Eyep.	Magn. p. tube pushed in	Magn. p. tube drawn in
I	1	X 100	X 187
I	2	56	100
2	1	56	100
2	2	31	56

	1	2	3	4	5
1°	38
2°	61
30	120
40	247	480	636	1039
6°	348	676	896	1264	4685
70	305	59)	784	1406	4100
8°	385	1137	1507	2263	7881

Eyep.	1	Î 2	3	1	! 2	i 'quot;3.....	Resolv.
Obj. 1	Tube in			Tube out			power
1	X33	X49	X83	X47	X71	X 120	Vl'OO mm
2	44	60	99	53	71	115	V400 gt;» ..
3	78	120	177	102	148	217	V(iOO quot; gt;gt;
5	254	323	526	326	434	; 676	'/l20() »gt;gt;1
8	400	568	864	543	771	i 1173	Vl 400 gt;» •lt;
9	425	604	918	577	820	1247	V1 fiOO .. M

Eyep.	I	2	1 3	4
1	X 60	X 90	X 135	X 190
2	200	300	I 440 1	630
3	350	520 1 1	780 1	1100

	Magnification								Resolv.		power (mm)
\Kyep				1
\	1	2	3	4	5	5'	6	1	2	3	4	5	5'
0bj\				1
2 4 5 7 8 9 11	18 40 80 135 215 300 340	23 50 100 170 275 380 430	31 70 140 230 360 515 580	48 105 210 360 575 665 900	57 125 250 425 680 950 1150	70 155 310 520 840 1150 1300	82 180 360 610 980 1350 1550	I itj îAïi aiir Tc'ffïï TîVïï To'oo TïVu	I off BAIT TiiVa 1 i'oo TDVU TgVn	îiïï OAK To'oTT T-l'off IB'OU To'oïï Ts'oa	is'od Ti'ïTU Tfl'oiï ToVff TBVÏÏ	lAo sAn Tî'nu I l'on Tfl'oO To'o® 15*05	lha s ho Tl'oîT n'oo lo'oo 1 o'oir Ts'oiJ	2A0 lAn nVff rAff iTj'oK TnVn

Obj. 1	^A'oo mm
2 3	Vcoo .... (with eye-piece 3 : Vsoo mm). Vsoo ....

Obj.	Magnification		Resoiv. p.
Obj.	Eyep. 1	Eyep. 2	Resoiv. p.
3	X 40	X 70	Vioo mm
2	92	160	ViJOO quot; '«
2 3	130	225	v.,00 ....

Eyep.	Magn. power			Resolv.
Obj.	I	2	3	power
single	X 105	X 125	X 225	V400
triplet 1	130	155	270	VGOO gt;• •»
2	155	185	320	Vgoo gt;• ••
3	220	265	455	Vl 000 •• 1gt;
.. 4	230	275	475	Vl 000 •gt; ••
.. 5	320	385	660	Vl 2 00 •• -1
.. 6	560	670	1150	Vl 400 gt;• '1
Nachet 7	660	790	1360	1 1 / 14 00 •• gt;•

	Magnification		Resolv. p.
	Tube drawn in \| Tube drawn out
Eye-piece 1, Eye-piece 2.	X 60 90	X 85 125	V400 mm V400

Eyep. Obj\	Magni		ication
	Tube in		Tube out		Resolv. p.
	1 3		1	3
1 3 5	X 55 165 240	X 130 380 560	X 80 230 345	X 180 540 800	V400 mm Vfi00~V800mm 'Viooo mm

	1	Magnification		i 1 1
Eyep.		i
	1	2	3	Resolv. p.
Obj. .
0	X 15	X 21	30	Vioo mm
1	37	52	75	200 quot; quot;
3	100	140	200	Vcoo
5	150	210	300	^/soo quot; quot;

	Magn.	Resolv. p.
one lens two lenses three lenses	1 X 35 50 100	VL'OO' mm V400 quot; Vnoo •gt;

• Lens	Magnification	Resolv. p.
1	X 55	oQo mm
2	34	V'loo ....
3	25	Vioo .... .
4	21

	Magn. p.	Resolv. p.
A. A slide with 6 small plano-con-
vex lenses (convex side turned
to the object):	X 52	^/aoo mm
	38	V200 quot; quot;
	33	V200 ....
	23	100 gt;. gt;.
	H	—
	11
B. Two larger projecting lenses of	1
low power (megaloscope):	8 5	—
C. A doublet lens:	i 32 1	V400

Group 1. V5000 inch	=	V197
2. 1/10000 quot;	=	V394
^/isooo quot;	=	V591
4. 1/20000 quot;	=	/ 788
5. V25000 ..	=	^/985
6. V30000 quot;	=	1180
7. 1/35000 quot;	=	/1380
8. 1/40000 ..	=	V1575
9. 1/45000	—	V1775
10. V.'ioooo	=	1970
quot; IL ^/sGOOO	=	V2I65
.. 12. i/eoooo		V2365