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NATURAL HISTORY
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THE MICROGRAPHIA.
Contents: — History and Description of Reflecting Microscopes — On Micro-
meters, and their Use — Monochromatic Illumination — Solar Engiscopes,
and the Exhibition of Tests by them — On trying Microscopes and
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MICROSCOPIC ILLUSTRATIONS
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CONCERNING THE MOST ELIGIBLE METHODS OF CONSTRUCTING
ffl\tvo$topt$,
AND INSTRUCTIONS FOR USING THEM.
By C. R. GORING, M.D.
A Neiv Edition, emended and enlarged.
By ANDREW PRITCHARD, M.R.I.
HON. MF.M. SOC. ARTS, EDIN. ; AUTHOR OF " NATURAL HISTORY OF ANIMALCULES,
&C. Aft
LONDON:
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1838
O PINION S
OK
SCIENTIFIC JOURNALS
OV THK FIRST RDITION OK THE
MICROSCOPIC ILLUSTRATIONS.
" Impressed as we are with the high importance of this branch of science,
and with the great value of the improvements which these gentlemen have
introduced, we looked forward with the most sanguine expectations and
have now no hesitation in stating it as our opinion, that Dr. G. and
Mr. P. have both accomplished their difficult tasks with the greatest success.
The coloured engravings are executed in such a masterly manner that they
will themselves bear to be seen by the microscope."
Brewster's Edinburgh Journal of Science.
" The present publication cannot fail to recommend itself generally, for it
is associated with elaborate descriptions and beautiful coloured engravings of
a variety of diverting and popular objects." — Journal of the Royal Institution.
" The notices of natural history in the volume before us are well arranged ;
the coloured engravings are executed with the most perfect fidelity ; 'and the
entire work will afford a high treat to the curious admirer of nature." — Atlas.
OPINIONS OF THE PUBLIC PRESS
MICROSCOPIC CABINET.
" This is an exceedingly curious and interesting work ; the plates are marvellous."
Spectator.
" We earnestly recommend the Microscopic Cabinet both to the general and the
scientific reader, as an original, a valuable, and an ingenious work."
London and Edinburgh Philosophical Magazine.
" We are presented," in the Microscopic Cabinet, " with engravings of the most
beautiful or remarkable water-insects, and are moreover informed of their history, habits,
and anatomical conformation. We have also directions as to the use of the instru-
ments employed in these researches, and a full description of Mr. P.'s new microscope.
* * * We cannot speak ton highly of the finished coloured engravings ; they are
equally remarkable for the fidelity and the beauty of their execution. A mere inspec-
tion of these would be sufficient to create a taste for the study of a department of
philosophy which certainly is inferior to none in the interest it is calculated to create,
or the elegance of form and the harmony of adaptation which it presents to the view."
New Monthly Magazine.
" This work may be termed a practical treatise on the present state of Microscopes.
In the descriptive portion, valuable information is imparted on the structure and habits
of those most interesting creatures," Animalcules, Crustacea, and Insects ; " and for
procuring-, feeding, preserving, and the best mode of examining them, useful directions
are given." Magazine of Natural History.
" This work selects a variety of living objects that have never been before described,
and depicts faithfully many others that have hitherto been most incorrectly represented.
The descriptions are most elaborately written in a plain and familiar style."
Monthly Magazine.
" A vast variety of practical information, popularly detailed, is diffused throughout
the work , and the whole is illustrated by a number of very beautiful plates. * * *
It is decidedly the most practical and satisfactory treatise on the microscope that it has
hitherto been our good fortune to have met with." London Medical Gazette.
" This is a very complete and interesting work." Athenarum.
" Many of the descriptions of the structure and habits of animals, as observed by our
Author, will be found curiously interesting. The style in which the work is got up is
very creditable, and the illustrations extremely good and copious."
London Medical and Physical Journal.
" The lovers of natural history will derive both gratification and instruction by the
perusal of this work." Register of Arts.
" This is a beautiful volume, which must be deeply interesting to those engaged in
the study of natural history. The plates are well delineated, beautifully coloured, and
afforded at a reasonable rate. It is impossible to speak in too high terms of its execu-
tion." London Medicul and Surgical Journal.
" Some of the best executed plates and cuts that we have seen on the subject. We
have no doubt that the present volume will go far to supply a desideratum ; and not
least as to the due appreciation of microscopes, perfection in the qualities of which is
obviously essential to the just characterization of the insect tribe."
Gentleman' 's Magazine.
" The greater part of this volume is taken up with descriptions of the economy and
nature of aquatic insects, Crustacea, and animalcules, written in a. popular style, without
any scientific display of terms to perplex the general reader, and is illustrated by some
admirably coloured engravings, of whose beauty and fidelity we can bear witness."
National Omnibus.
" The Microscopic Cabinet will essentially aid the cause of science." Atlas.
" This is a valuable work for scientific men, and of great assistance to the student of
botany or natural history." Bell's Old Weekly Messenger.
" The Microscopic Cabinet is a work which does almost infinite credit to its authors,
and is certainly by far the most valuable contribution which has been made to micro-
scopic science in modern times." Mechanics' Magazine.
PREFACE.
At the period of the publication of the first edition
of this work in 1829, microscopes on the new prin-
ciple had only just sprung into being, and some
apology for a treatise upon an instrument which
then apparently had little but novelty to recommend
it, might have been thought requisite; since that
time, however, its application to the sciences, and
the pleasure derivable from it as a source of amuse-
ment, have rendered this unnecessary.
It will be found that the present arrangement
of the papers is different to what it was in the first
edition, that having been suited to their being' pub-
lished in numbers, which occasion being done away
with, Dr. Goring's are now placed together, and
with them the description of his instrument.
In the first chapter of this volume the reader is
10 PREFACE.
furnished with a brief sketch of the uses of the
microscope, and its various improvements. This
appeared to be preferable to commencing- with the
original Exordium, on account of the progress
microscopic science has made in public opinion, and
the enlarged view which is now taken with respect
to the microscope. As, however, there are many
persons who desire and expect to meet with the
Exordium in the present edition of this work, it
has been deemed advisable to give it entire in the
Appendix, with Dr. Goring's corrections.
The three succeeding chapters are appropriated
to a description of certain living microscopic objects;
and containing, as they do, some remarkable parti-
culars relating to the wonderful metamorphoses
which these creatures are ordained to undergo, it
is confidently hoped they will not be deficient in
interest or instruction.
The remaining portion of the volume contains an
account of the mechanical construction of the micro-
scope and its apparatus; and since we have no
other work devoted to this branch of the subject,
affording to all persons possessing this instrument
such practical instructions as are absolutely neces-
. PREFACE. 1 1
sary for the right using1 and managing of it, it is
fairly presumed that this will be serviceable. These
instructions, it may be as well to mention, are not
confined to any particular sort of microscope, but
are purposely drawn up in general terms, in order
that some profitable information may be gleaned
from them, in the management of any microscope
whatever, no matter what may be its optical con-
struction.
From the rapidity with which one improvement
has succeeded another, it is necessary, in order to
come at a right conclusion as to the relative merits
of the productions of different artists, to take the
time at which their instruments were fabricated
into consideration ; for, should some of them have
been made three or four years before the others,
the latter will in all probability excel the former;
whereas, had a comparison been instituted between
the simultaneous productions of the artists, the result
might have been quite the reverse.
In the explanation I have given of that remarkable
instrument, the Polarizing Compound Microscope, it
will be found that I have gone somewhat minutely
12 PREFACE.
into detail respecting it ; and, with a view of render-
ing' it as available as possible, have printed in the
Appendix Mr. Talbot's highly interesting papers
upon the polarizing properties of crystals. Although
this is in itself almost a new instrument, a great
deal has already been accomplished by its means,
and a great variety of the hidden phenomena of
nature most beautifully displayed.
The kind consideration bestowed upon the first
edition by men the most distinguished in science,
who had turned their attention to this subject, and
the interest now so generally felt in microscopic
researches, induce me to hope that the present
volume — a large portion of which has been re-
written, expressly that it should contain the latest
improvements — will be favourably received.
ANDREW PR1TCHARD.
102, Fleet Street, London.
CONTENTS.
Page
Preface 9
CHAPTER I.
Introductory Remarks on the Application of the Micro-
scope to the Sciences, with an Account of its recent
Improvements 17
CHAPTER II.
On the Larva and Pupa of a Straw-coloured Plumed Culex
or Gnat 50
CHAPTER III.
On the Larva and Crysalis of a Day-Fly 61
CHAPTER IV.
On the Larva of a Species of British Hydrophilus 70
CHAPTER V.
On the Terms employed in Microscopic Science —
With a Description of the Vertical Microscope - ;i
31 2 3 4
14 CONTENT?.
CHAPTER VI.
Page
A Description of the Achromatic Microscope, together with
its Apparatus, and the mode of using it : —
Round Stand Microscope — Solid Tripod -stand Microscope —
On selecting Magnifying Powers — Candle- holder, Shade, and
Condenser — Spring Double-Stage — Moveable Stages — Spring
Phial-Holder — Polarizing Microscope — Apparatus for Dis-
secting— Simple Lenses mounted in imitation of Achromatics
— Garden Clamp for the Microscope — Steadying Rods — Camera
Lucida, for Drawing— Micrometer Eye-pieces— Method of
Viewing Moveable Fluids in the Cavities of Crystals — Concave
Specula, Silver Cups, &c. — Stops, or Diaphragms — On View-
ing Transparent Objects by Daylight — On Viewing Bodies by
Intermitting Light — Black Ground Illumination for Transpa-
rent Objects — On Viewing Opaque Bodies by Oblique Reflected
Light — Method of determining the Forms of Minute Bodies —
On Viewing the Currents in Fluids during Evaporation 85
CHAPTER VII.
Practical Remarks on Microscopes for viewing and drawing
Aquatic Larvae, &c. — By C. R. Goring, M.D 146
CHAPTER VIII.
Whether there is a best possible way of constructing the
Stand, or Mounting, &.c. of Microscopes (the specific
purpose or purposes to which they are to be applied
being first determined) — By C. R. Goring, M.D 150
CHAPTER IX.
Description of Dr. Goring's Operative Aplanatic Engiscope 168
CONTENTS. 15
CHAPTER X.
Manner of Observing with and Managing the Operative
Aplanatie Engiscope : —
General Observations— Method of Mounting for viewing Inani-
mate Transparent Objects by pure intercepted Daylight —
Method of Mounting for viewing Transparent Objects by
Artificial Light — Mode of Mounting for viewing Diaphonous
Bodies by reflected Daylight, either in a horizontal or vertical
position — Way of Viewing Crystallizations of Salts and various
Chemical Actions— Way of Mounting for Transparent Living
Objects — Method of Mounting the Diamond and Sapphire
Microscopes for Transparent Objects — Opaque Objects —
Method of observing Opaque Objects by Daylight, plain or
condensed — Silver Cups or Specula — Mounting for Dissections,
&.C.— Mounting the Diamond and Sapphire Microscopes for
Opaque Objects — The Amician Catadioptric Engiscope. — By
C. R Goring, M.D
Page
17!>
APPENDIX
No. 1.
On the Optieal Phenomena of certain Crystals. — By H. F.
Talbot, Esq. F.R.S 213
No. 2.
Further Observations on the Optical Phenomena of Crystals.
— By II. F. Talbot, Esq. F.R.S. 219
No :).
Exordium.— By C. R. Goring, M.D 232
No. I.
Swammerdam's Method of Dissecting and Preparing Objects
for the Microscope '211
ERRATA.
Page 87, lines 1 and 14, for Chapter VIII. read Chapter IX.
— 93, line 10, for Chapter VII. read Chapter VIII.
CHAPTER I.
INTRODUCTORY REMARKS
APPLICATION OF THE MICROSCOPE TO THE SCIENCES, WITH
AN ACCOUNT OF ITS RECENT IMPROVEMENTS.
" THERE IS PROBABLY NO BRANCH OF PRACTICAL SCIENCE WHICH HAS
UNDERGONE SUCH ESSENTIAL AND RAPID IMPROVEMENTS AS THAT WHICH
RELATES TO THE MICROSCOPE. IT HAS BECOME QUITE A NEW INSTRUMENT
IN MODERN TIMES, AND IT PROMISES TO BE THE MEANS OF DISCLOSING
THE STRUCTURE AND LAWS OF MATTER, AND OF MAKING AS IMPORTANT
DISCOVERIES IN THE INFINITELY MINUTE WORLD, AS THE TELESCOPE HAS
done in that which is infinitely distant." — Sir David Brewster*.
Whtlst the mind dwells with the highest admiration on
the rapid advances which are daily and hourly being1
made in the pursuits of science, we are recalled almost
naturally to what is perhaps one of the most important
considerations connected with this deeply interesting
subject, — namely, how it is that we are thus enabled to
make discovery after discovery into the inexhaustible
treasures of Nature, and by the help of what machinery
it is that we are making this astonishing progress. To
investigate the genius and faculties of the human mind,
the primum mobile in devising all that is great and all
* Encyclopaedia Britannica, 7th edit. art. Microscope.
C
18 MICROSCOPIC ILLUSTRATIONS.
that is valuable, would fall within the province of the
profound metaphysician, rather than that of the practical
man of science ; but to elucidate the methods by which
genius is aided in its high researches after truth, and in
conducting those researches to their desired proficiency,
although an occupation of a much humbler grade than
the other, is one, nevertheless, that is by no means insig-
nificant, or devoid of interest.
Thus, for example, an illustration of the improvements
effected in the optical construction of the telescope, by
which the astronomer may attain to a more perfect know-
ledge of the celestial bodies — by which he may discover
worlds beyond worlds innumerable, and read the laws by
which all those worlds are governed — cannot be deemed
either unimportant or uninteresting. The invention of
this beautiful instrument gave a powerful impulse to the
human mind towards the study of astronomy, and every
improvement since made upon it has laid open new
sources of knowledge in that science, and created a
greater zest for its acquisition. Even the splendid dis-
coveries of the immortal Newton on the theory of the
Moon, until verified by the observations of a Flamstead,
by means of astronomical instruments, could not be
received as the actual laws which govern that satellite.
Even since these great discoveries, which carried the
mind of man into the immensity of the heavens, and
gave him a far more extended idea of the creative power
than any thing could possibly have given him before,
what has not the astronomer been able to effect through
INTRODUCTORY REMARKS. 19
the vast perfection to which the telescope in more recent
times has heen brought ? I need only mention the dis-
covery of the aberration of light ; the resolution of
nebula? and of the double stars ; the motions of these
binary systems, and their subservience to the same law
of gravitation as governs the solar j the position and
direction of the latter in space: — I might mention many
others, all equally important — all marvellously grand !
And so with respect to the Microscope in aiding to ex-
tend our knowledge of the economy of this planet. Every
improvement in this instrument has developed some im-
portant feature in the structure and design of the almost
infinitely varied organized beings of our earth. The
achromatic principle, which was at once adapted to the
telescope with the most astonishing success, did not
produce the same happy result on its first application to
the microscope. The recent discovery of Dr. Goring,
that the penetration of this instrument was dependent
upon the angle of aperture, or the number of rays of
light collected by the object-lens from every point on the
surface of the object, was requisite for the accomplish-
ment of this desirable purpose. By thus applying the
achromatic corrections and those for sphericity to this in-
strument, it has now been perfected, and elevated to a
grade nowise inferior to the telescope. The fruits of
this discovery are fast pouring in upon us, and promise
to yield a rich and most abundant harvest. We will al-
lude cursorily to some of those which have been reaped
already ; a few only will suffice to shew their importance;
20 MICROSCOPIC ILLUSTRATIONS.
and to claim for the microscope a high rank among"
optical instruments.
The fact is, that since the modern improvements the
microscope has undergone, it is being brought to the
assistance, and is at the present time furthering the pro-
gress of almost every branch of natural science. To the
Geologist it may be said to be a new instrument. But what
has it not even now effected for him ? In his study of or-
ganic life and structure, it has unfolded to him the pre-
cise characters of divers animals and plants which inha-
bited and clothed our earth in ages which have long
passed away. Look at the discoveries of Agassiz on the
fossil creatures of the deep ! By a microscopic investi-
gation of such portions of them as have withstood the
destructive power of time, namely, their scaly covering,
he has been able so to group and class them, that the
characters and habits of the genera belonging to each dis-
tinct era are clearly demonstrated. A microscopic exa-
mination also of the testaceous remains of sundry Ento-
mostraceans found in slate-clay formations, now ele-
vated much above the level of the sea, prove them to
have been at some time or other imbedded in the waters.
And the Naturalist may even determine by his inspection
of the shell, whether the species were the inhabitants of
fresh or salt water, and consequently whether the strata
themselves were the indurated beds of the sea, or of some
river or lake.
The most perfect animal remains which the microscope
has disclosed to us, are the various loricated Infusoria
INTRODUCTORY REMARKS. 21
of the division Bacillaria*. These minute creatures are
so inconceivably numerous that they cover many miles
of surface with several feet of thickness ; as instanced
in the polishing-slate and rotten-stone of Bohemia. In
Tuscany whole mountains consist almost entirely of the
silicified shells of these creatures ; thus combining with
each other in infinite numbers, to counterbalance, as it
were, their individual minuteness, and to teach the un-
thinking this useful lesson, that Nature, in all her ope-
rations, is never employed in vain, and that, what are ap-
parently her most insignificant productions, fall not be-
neath the notice of the profoundest inquirer after truth.
To the Botanist the aid of the microscpoe is indispen-
sable. In the investigation of our fossil-flora, what does
it not exhibit to us ! How beautiful and delicate is the
structure of the envelope of some of the fossil-fruits ; those,
for instance, of our London clay, when viewed under this
instrument! And how important is it, that, by its assis-
tance, we can determine with accuracy the natural orders,
genera, and sometimes the very species of the trees and
plants of former epochs ! How, beyond all question, is
now demonstrated the vegetable origin of our coal !
Preserved within a bituminous lump of coal, which has
been deposited for thousands of years deep in the bowels
of the earth, you may discern not only the woody fibre,
its arrangement, and the disposal and form of the
medullary rays, but even the most delicate of the vege-
table organs, such as the spiral vessels and the beautiful
* See Natural History of Animalcules, page b'.K
22 MICROSCOPIC ILLUSTRATIONS.
terminations of those vessels ! These are as distinctly
discoverable as in the finest preparations of a recent plant.
And what can be more amusing and instructive than the
examination of the silicified woods, when formed into
sections no thicker than the paper of a Bank-note?
Thus rendered pervious to light, the organic structure of
the wood becomes plainly distinguishable. And ema-
nating from this, what can be a more interesting subject
than the inquiry into the mode in which the silicifying
process has been carried on — by which the constituent
elements of the inmost and minutest portions are changed
—whilst their form and situation and colour remain the
same ? In investigating also that extinct genus of plants,
the Lepidodendra, a similar idea is raised in the mind, as
to what must have been the particular state of the earth
with respect to atmosphere and temperature at the pe-
riod of their growth, and what the changes which have
since taken place, in order to bring it to its present
condition.
In our physiological inquiries into the animal and
vegetable productions of the present time, the assistance
of the microscope is essentially requisite. When Dr.
Harvey made his grand discovery of the circulation of
the blood, and first lectured upon it, in St. Bartholo-
mew's Hospital, in 1619, he was ridiculed, and lost his
practice, through maintaining what was then supposed
to be so absurd and wild a theory. The idea was
suggested to his mind by reflecting on the valves of the
heart and veins, which were evidently so planned as to
INTRODUCTORY REMARKS. 23
allow a fluid to pass but one way. All the philosophical
reasoning, however, of this celebrated man could not
establish, what appears to us so plain a truth, until it was
evidenced in the circulation of cold-blooded animals by
means of the microscope, and thus placed beyond a
doubt. Discerning, as we can do, the very forms of the
globules of that fluid, as they flow through the capillaries
from the arteries to the veins, in obedience to the laws
impressed upon them by the Almighty Creator — viewing
this most sublime phenomenon, by which life itself is
diffused throughout, and sustained in every part of the
system — who can resist conviction of the great truth ?
Nor is it a matter of less importance in a scientific
point of view, or less interesting, that by the same
means we can perceive the fibrous structure of the
muscles and nerves, the form and arrangement of the
canals by which the internal cavities of the bones are
lubricated and nourished, the glandular structure of that
beautiful and complex apparatus by which the secretions*1
are carried on — all, and each of these, requiring but the
aid of one of our improved microscopes to render them
distinctly visible. Again : how admirably developed by
means of the microscope are the curious and complex
structures of the eyes of insects, the crystalline lenses of
those of fish, birds, &c.f and many of the other parts of
the visual organs];. The eye — that useful and delightful
* Nouvelles Rccherches sur la Structure de la Peau, par M. Breschet.
I Philosophical Transactions, 1833.
I Sec Langentoeck ou the Lye.
24 MICROSCOPIC ILLUSTRATIONS.
portion of us which furnishes all the endless variety of
objects from which we derive so great enjoyment —
resembles, in its peculiar formation and arrangement, an
achromatic optical instrument. And if we descend to
the lower classes of animals — nay, I would hardly say
lower, lest some perhaps might imagine that in their
small forms they do not evince as much perfection as is
discoverable in beings of a higher scale, and have not
all the functions which are necessary to life as full in
operation as even man himself— if we enter upon an
investigation of their minute structures, we can deter-
mine absolutely nothing without the microscope ; and
our knowledge of the very existence of many highly-
organized and active creatures is wholly dependent
upon it.
Vegetable organography, upon which the modern
botanist depends so much for his systematic arrangement,
and with which the student is so greatly interested and
amused, owes almost its very existence to the microscope.
This observation will be found to apply in an especial
manner both to the cellular and vascular tissues of plants.
The membranous cellules of cellular tissue are some-
times not more than 1- 1000th of an inch in diameter;
and those of the ordinary size are about 1 -200th or
l-300th. How, then, is it possible that we could become
acquainted with their forms and arrangement but by the
aid of the microscope? And so with respect to vascular
tissue : it is absolutely indispensable toward acquiring
an accurate knowledge of the structure and forms of
INTRODUCTORY REMARKS. 25
these membranous tubes, and of the spiral or annular
fibre which surrounds them.
A knowledge of the fructification, if I may so express
myself, of that numerous and curious class of plants, the
Acrogens, could not be obtained without it ; nor could
the existence of many of them, such as the Fungi,
Lichens, Algae, and some of the Musci, be proved. By
its powers even the ashes of vegetables may be seen to
contain the decisive characteristics of organic structure ;
and the long-debated question of the antiquarian, as to
whether the " fine linen of Egypt," in the times of the
Pharaohs, were of linen or cotton fibre, seeing the
latter is now indigenous to that country, is for ever set
at rest.
In many of the larger portions of plants, such as the
cuticle of their leaves, the stomata, &c. which require
but a shallow magnifying power to display them, there
is as great a difference manifested when these are viewed
under an achromatic microscope, or under the old com-
pound, as is perceptible between the most highly-finished
miniature, where the most delicate features and even
the down on the skin are correctly depicted, and the
mere black and white profile, where we see but the rude
contour of the face. Surely, then, as works of art
merely, instruments which can effect so much as this
are justly entitled to a due share of consideration even
from the most refined and polished minds.
In the foregoing remarks on the application of the
microscope to botanical purposes, I have given the
26 MICROSCOPIC ILLUSTRATIONS.
reader only a general outline ; to enter upon any thing
like details would of necessity extend an introductory
chapter of this description far beyond its proper bounds.
I may, nevertheless, be permitted to make use of one
example by way of illustration. But how shall I select
one where the materials suited to construct it are so
superabundant, and where they all present so many
points of interest ? It will be readily admitted that this
is by no means an easy choice. I will limit my obser-
vations, however, to a single microscopic slider, and see
what instruction is derivable from it. Suppose this
slider to contain some sections of a recent or fossil wood ;
for instance, three specimens or shavings of such ex-
treme tenuity, that if they were exposed, they would be
wafted away on the slightest breeze. Let them be
weighed, and they will not exceed a grain. Hand them
to the chemist, and he can only prove to you that their
primary constituents are oxygen, hydrogen, carbon, &c.
and in so doing he will destroy them. What, then, does
an inspection of them under the microscope reveal ? It
will tell you, in the first place, whether they grew up,
like our forest trees, by yearly additions to the outside of
their woody centres, or by internal accessions, like most
of the productions of the tropics. It will tell you
whether their leaves were veined or not — whether their
embryos were dicotyledons or monocotyledons — whether
the trees from which they were cut had branches or not —
and, if they had, whether these were thick and sturdy,
like the boughs of the oak ; or thin and flexible, like the
INTRODUCTORY REMARKS. 2J
branches of the fir tribe. It will tell you whether the
wood might be easily cleft asunder, like deal; or would
sooner break, like beech ; whether it was elastic, like the
pine — so admirably suited for the masts of ships; or, like
the stubborn oak, would rather snap than yield to the
wind. These are some of the ordinary properties deve-
loped by the microscope.
Again, in taking a more minute physiological survey,
our information will be by no means less complete. For
these same specimens will disclose to us, under the
microscope, the form and arrangement of their woody
fibres, the disposition of their barks, the beautiful struc-
ture of the tubular receptacles, by which their secretions
have been carried on and their growth promoted. In
short, so much will be revealed by them in this manner,
that the actual distinction between a wild and a culti-
vated tree may be, in some cases, clearly traced. " Thus,
in the cultivated cherry, the plates of the medullary rays
are very thin, the adhesions of them to the bark are very
slight, and hence a section of the wood of that plant ex-
hibits a pale, smooth, homogeneous appearance ; but,
in the wild cherry, the medullary plates are much thicker,
they adhere to the bark by deep broad spaces, and are
arranged with great irregularity, so that a section of the
wood of that variety has a deeper colour, and a twisted,
knotty, very uneven appearance*."
Should they be specimens of endogenous woods (ver-
* Lindley's Botany, page 241.
28 MICROSCOPIC ILLUSTRATIONS.
tical sections of which I have at some expense and
trouble lately introduced,) what a volume of instruction
may be derived from them ! whilst the exquisite beauty
and lace-like form of the transverse cuttings will bid de-
fiance to every attempt at describing them !
In order that this class of microscopic objects may be
rendered as useful as possible, it may not be unimportant
to suggest that collections of thin sections of woods should
be selected according to the natural arrangement of
plants. In the cases I have lately mounted, an example
is given from all the principal groups ; and where the
genera, in any natural Order, are very dissimilar, two
specimens are taken, for the purpose of instituting a
comparison between them.
I need hardly mention how essential is the aid of the
microscope to the Mineralogist in determining the
crystalline structure of a body. In the study of crys-
tallography, which science may be said to have been for
a long time almost at a stand-still, a very extensive field
of research appears to be now opening by the adaptation
of polarized light to a microscopic examination of minute
crystals, thus eliciting a great variety of curious and
beautiful properties, entirely unknown to the world be-
fore. This subject being as yet completely in its infancy, it
would be unfair to expect an elucidation of it at the present
time. To convey, however, some general idea to the reader
of the additional degree of interest which attaches to the
phenomena of crystallization by this happy contrivance, it
INTRODUCTORY REMARKS. 29
is only necessary to state, that we have now displayed
to us minute crystals, with a brillancy and richness of
colouring that is quite inconceivable. We see the smallest
difference in their thickness marked by some exquisite
change of colour ; whilst the beautiful black cross in the
circularly arranged crystals of zanthate of ammonia, and
the cross with the coloured rings in the compound of phos-
phoric acid and borate of soda, &c. &c. excite our admi-
ration beyond all bounds. These newly-discovered phe-
nomena, after a patient investigation, may lead to results
highly interesting, and of great importance to science.
By a simple modification of its polarizing apparatus,
the microscope becomes of great value in investigating
some of the physical properties of matter : it is capable
of being constituted a complete polariscope, and made to
exhibit the phenomena of polarization in plates of crystals
cut perpendicular to their axes ; for instance, the coloured
rings, the black cross, the tints of unannealed glass, of
amethyst, &c.
When relaxing from the stern pursuit after the exi-
gencies of life, where, perhaps, we may have been in-
dustriously labouring to benefit the -condition of our-
selves or families, what a delightful and inexhaustible
source of amusement is ever open to us where a good
microscope is at hand ! It is not always an easy task to
find innocent amusement : to find it blended with im-
provement is to find it indeed. We may, it is true, be
entertained by the veriest trifles in life, but we shall soon
grow weary of them ; and even the converse of intimate
30 MICROSCOPIC ILLUSTRATIONS.
acquaintances at times becomes vapid and dull. A re-
creation, to last beyond an hour, must be made to instruct
as well as to amuse \ it must, to a certain extent, be
commensurate with what a rational and intelligent mind
is in quest after, or we shall speedily be thrown upon
our resources to find out a new one. A good micro-
scope, as I have said, is a never- failing source of amuse-
ment. Were we permitted to draw a comparison be-
tween it and that grand and noble instrument, the tele-
scope, we should be compelled to admit that it possesses
very many advantages even over that instrument in this
respect. We can use it at all times and seasons, and that
with the greatest facility. We can invite our friends to
pass an evening with us in being gratified with its per-
formance, without any fear of encountering a disappoint-
ment. Not so, however, with the telescope. A few nights
only throughout the year are what we may term good for
astronomic purposes, and over these few we can exercise
no control. Our friends may be invited — they may assem-
ble— and the weather may prove so inauspicious as to
render the finest instrument in the world of no avail. And
even on the clearest night, when all our expectations are
raised to the highest pitch, the wind may suddenly shift,
so as to occasion the greatest interruption ; so that, per-
haps, the very means we have taken to expand and ele-
vate our notions of the infinite wisdom and power of the
Divine Being, may terminate, through some mishap, in
ruffling our minds, and causing an effect the very
opposite to that we had designed to produce.
INTRODUCTORY REMARKS. 31
The valetudinarian dare not seek his pastime from the
employment of the telescope ; were he to do so, his
career would soon be stopped, inasmuch as his remain-
ing out exposed to a few cold, damp nights, would at
once prove fatal to him. And even those who are in the
full enjoyment of health may suffer very materially by
prolonging their observations with a view of attaining to
some proficiency in astronomical pursuits ; to say
nothing of the inconvenience it occasions by breaking in
upon that regularity which is so essential to the comfort
and happiness of life. To the professed astronomer these
remarks are not of course addressed ; with him such dif-
ficulties as these do not, and ought not, to have any
weight. My object was to institute something like a
comparison between the telescope and the microscope
as to their capability of affording rational amusement to
the generality of mankind, when it is desirable to be-
guile a vacant hour, and where our whole time is not at
our own disposal. In making out my case in favour of
the microscope in this respect, I may be allowed to refer
the reader to such proof as is afforded by the subjects
treated of in the first three chapters of this work.
" These," saysDr. Goring, whenspeakingoflivingobjects
viewed under the microscope, " experience has shewn to
excite the strongest emotions of pleasure and satisfaction
in the great mass of observers of all ranks, whom I
have always found to be most delighted by comparatively
large living objects, seen with medium powers. In fact,
they seem to afford the same sort of gratification with a
32 MTCROSCOPIC ILLUSTRATrONS.
menagerie of living wild beasts on the large scale ; and
most certainly many of them wonderfully emulate the
ferocity, voracity, cunning, and cruelty of the mammalia.
They prey on each other, and fight with a degree of
determined obstinacy, not inferior to that of any beings
whatever. They have likewise a thousand diverting
pranks and humours, quite peculiar to themselves. In
addition to these amiable and amusing qualities, they
possess such a high degree of transparency, that their
unique and beautiful internal machinery is as clearly
perceptible as if they were made of glass ; so that, with-
out any dissection, we can unravel all the mysterious
workings of their nature ; such as the circulation of the
blood, the pulsations of the heart, the peristaltic motion
of the intestines, and the play of every muscular fibre.
This property of transparency is not possessed by any
other living beings with which I am acquainted, except
the Animalcula infusoria. I may observe, that no perfect
insects present so many facilities for adaptation to the
microscope, or can be so easily preserved and managed;
so that the larvse, &c. appear to me peculiarly and ex-
clusively devoted to the consideration of microscopists*."
Having now given a brief outline of the uses to which
the microscope may be applied, we will proceed to con-
sider those practical improvements which, in modern
times, the instrument itself has undergone, and which,
step by step, have at length brought it to its present
high state of perfection.
* Exordium, first edition, p. 6.
INTRODUCTORY REMARKS. 33
Microscopes may be classed under two denomina-
tions, simple and compound.
The simple microscope presents an object to our view
under a greater angle than that which it is seen under
when viewed by the naked eye ; whence it is that the
impression is derived of it being amplified or magnified.
The amount of this amplification will be in precisely the
same ratio as that when a person is seen at different
distances from us : the nearer he is, the greater is the
angle he will be viewed under ; and so vice versa.
Hence it is, that a lens which will admit of an object
being placed within one inch of it, will amplify twice*
as much as another the focal length of which is two
inches. This quality, viz. the focal length of a lens, or
its power of admitting an object within a definite distance,
so that it may be distinctly visible, is obtained by giving
to the surface of any transparent medium (say glass) a
spherical or other curved figure. Now it will be evident
that, on account of the curvature which is thus given,
the rays of light which proceed from any given point in
an object to the middle of the lens will pass in a more
direct course through it (assuming the lens to be convex)
than those which proceed from the same point to the
outside or edges ; and consequently the former will be
less refracted or bent in their passage than the latter.
All the rays, therefore, after permeation, will not proceed
towards the same point in the axis of the lens, but
crossing it at different distances they will enter the eye
* Sec Mirrofjrapliifi, pnero 63<
D
34 MICROSCOPIC ILLUSTRATIONS.
confusedly, and produce a nebulous or indistinct impres-
sion of the magnified object. This defect is commonly
designated spherical aberration. Another obstruction to
perfect vision is occasioned by the effect produced upon
the light itself, when passing from one medium into
another of different density. Light (say common white
light) is a compound of coloured lights, which are not
equally refrangible ; that is, some of the colours are
more powerfully acted upon by a refracting body than
others ; so that a white ray, when it enters a lens, is more
or less broken up and separated into its coloured con-
stituents, which gives a semblance of colouring to the
object Ave are viewing. This defect is termed chromatic
aberration, or dispersion.
These two great defects are to be obviated in con-
structing a microscope. Until within a few years, the
lens of a simple microscope consisted of a single piece of
glass made into a curved form, or a spherule. In order
to increase its magnifying power, i. e. in order to admit
an object being placed very near the lens, so that it
might be viewed under a greater angle, Di Torre,
Leeuwenhoek, and others, constructed lenses of spherules
of exceeding minuteness — some, it is recorded, with a
focal length of not more than 1 -700th or 1- 800th part of
an inch. This method of obtaining high magnifying
powers was attended with so much inconvenience in
practice that it counterbalanced all the advantages which
would otherwise have resulted from it. Whilst the
obstructions to vision just mentioned, viz. spherical and
INTRODUCTORY REMARKS. 35
chromatic aberration, were obliged to be remedied in
a low power by placing a diaphragm or stop behind the
lens, so as to reduce the aperture ; by which means so
much of the light transmitted by the lens was cut off, that
the delicate structure of an object was hardly visible for
want of light.
The calculations of Euler and other mathematicians
were soon directed towards finding out such forms for
single lenses as would occasion the minimum quantity
of aberration. Still, the microscope derived but little
practical advantage from their investigations ; and the
reason of it I apprehend was this : their formulae were
all calculated for lenses of very small angular aperture,
whilst the goodness of a lens for the microscope depends
upon the opposite extreme.
In 1824, in consequence of Sir D. Brewster's remarks
on the diamond, I commenced making lenses of precious
stones*. These, when the stones are clear, free from
flaws, and from double refraction, are the most perfect
single magnifiers we at present possess.
From the period just named, a new era sprang up in
the history of the microscope. In 1829|, Dr. Wollaston
sent forth to the world his doublet lens, which consisted
of two plano-convex glasses. This invention, the result
of experiment, caused a most astonishing alteration for
the better in the constructing of microscopes. It sug-
gested the idea of employing more than one glass in
* See Microscopic Cabinet, chap. 14.
t Philosophical Transactions, 1830.
36 MICROSCOPIC ILLUSTRATIONS.
constituting a deep magnifier ; and the consequence was,
that we had soon devised for us a triplet, composed of
three plano-convex lenses, which is by far the most
perfect construction employed in simple microscopes.
I may remark, however, that the use of these compound
magnifiers is limited to the examining of delicate trans-
parent objects which admit of being brought almost in
contact with the lens. I may mention another improve-
ment, though perhaps rather prematurely, viz. that the
achromatic object-glass may be used as a simple micro-
scope, and with very great advantage when the magni-
fying power is moderate*.
We now proceed to consider the improvements which
have been made in compound microscopes. The com-
pound, unlike the simple microscope, in which we look
through the magnifier at the object itself, is furnished
with a second magnifier, designated the eye-piece, through
which the sight is directed, not to the object, but to an
image of it, which has been magnified by the first lens,
or, as it is called, the object-ylass. Now, we have noticed
that the best magnifiers of simple microscopes are in fact
compounds, being composed of two or three lenses ; but
yet they have not the double action of a compound
microscope, even should it be composed of only two
lenses. Dr. Goring, however, to prevent any confusion
arising between the one and the other, proposed the
* See Chapter X.
INTRODUCTORY RKMARKS. 37
name of Engiscope* for the instrument we are now
considering.
In this instrument, it is of the utmost importance that
the object-glass forming the image, which is to undergo
a second amplification by the eye-glass before it meets
the eye, should be as perfect as it can possibly be made ;
becauge, every error occasioned by it will be magnified
by the eye-glass, and thus cause very great confusion.
Dr. Goring having this in view, directed the late Mr.
William Tulley, in 1824, to make him a triple achromatic
object-glass, for a compound microscope. With this,
after many trials, during which the Doctor had contrived
to enlarge the aperture of his lens, he found that he
could distinguish some delicate markings on certain
animal tissues, which, with equal magnifying powers
having less aperture, he had not been able to discern.
Hence originated the discovery, that the penetration
of a microscope is dependent upon the angle of aperture
of its object-glass.
As this discovery has tended, in a great measure, to
bring the microscope to a high state of perfection, I may
be permitted to give a familiar explanation of the reason
why an increase of aperture is so efficacious. For the
details of the subject, the reader is referred to Dr.
Goring's own account, in the Micrographia, Chap. VII.
I am the more anxious to give this explanation, because
many persons are at a loss to conceive how it is that in
a compound achromatic microscope, where the light has
* See Chapter VII.
38 MICROSCOPIC ILLUSTRATIONS.
to pass through several glasses, each of which impedes a
portion of the rays, whilst others are lost by reflection at
the surfaces, that more should remain for the purpose
required than when a single glass is employed.
Every one who has considered the subject at all, will
understand that by a series of glasses of different media,
aberrations, &c. may be corrected and almost entirely
dismissed ; but it is not so readily perceived how a
compound microscope, having a series of glasses, can,
with less illumination, give a brighter and more vivid
picture, with more of the detail or minute structure of
an object, than can be obtained with greater illumination,
by a single lens. In this particular, however, consists
the main advantage of an achromatic.
Let me premise that, in order to render any object
visible, it is necessary that rays of light should proceed
from it, either by reflection from its surface, or by trans-
mission through it, to the eye. Again, if the number of
rays be insufficient, the object cannot be seen, notwith-
standing we employ a microscope for the purpose.
Bearing this in mind, I will endeavour to explain how
an increase of angular aperture in an object-glass,
independent of any increase of its magnifying power,
will admit a greater quantity of light from any given
point on the surface of an object to pass through the lens,
so as to render the structure of the object visible.
Let a, and «, represent two objects, in all respects
alike, and let us employ two microscopes, of equal
magnifying powers, for the purpose of viewing them.
INTRODUCTORY REMARKS.
39
Suppose that we are going to look at some spot on the
surface of a, or a, which we will imagine to be a delicate
Fig. 1.
Fig. 2.
tissue. By a well-known law of light, the rays proceed
in right lines, in all directions, from this spot, in the
manner shewn by the dotted lines in both figures.
Suppose b, b, and b, b, to be two object-glasses, of equal
focal lengths ; the former a single lens, of the best
construction, such as was used in the old compound
microscope, and the latter a lens of the newest form,
termed an achromatic. Now, these object-glasses will
form their respective images at i, and i, and they will be
of equal dimensions. But if the number of rays pro-
ceeding from a, and falling upon the single lens b, h, is
40 MICROSCOPIC ILLUSTRATIONS.
not enough, when collected at i, sufficiently to stimulate
the eye, any minute pore, striae, or other marking at a,
will not be rendered visible ; whilst, from the increase
of aperture in the achromatic lens, b, b, allowing much
more light from a, to fall upon it, and to be transmitted
through it and collected at i, every marking, &c. at a,
will be clearly represented at i ; and the eye, being
powerfully acted upon by this increase of light, will
become highly sensible of it.
The angles b, a, b, and b, a, b, are the angles of aperture
of the respective object-glasses ; and the quantity of
light collected and transmitted by each will be as the
squares of b, b, and b, b, the focal lengths being equal.
Hence it is that the power of a microscope, or that
faculty it possesses to render the structure of an object
visible, depends upon the angle of aperture of its object-
glass, and not upon its magnifying power alone.
But it may be supposed, perhaps, from this reasoning,
that if we throw a greater quantity of light upon an
object, so that more may be collected by the object-glass,
we shall be the better able to define its structure ; which
would probably be the case if the additional light could
be thrown only upon those minute parts which we wish
to examine, and not upon the whole object. But as we
cannot do this — as the increase of illumination cannot be
made to increase the relative proportions of light which
proceed from these minute parts, the intended advantage
will not be derived.
Having shewn, however, that the goodness of a
INTRODUCTORY REMARKS. 41
microscope is chiefly dependant upon the angle of aper-
ture of its object-glass, (freed from the aberrations just
mentioned), it is of some importance to be able to mea-
sure this angle with accuracy. When the object-glass
consists of a single lens, or of two cemented together,
its angle of aperture may be easily determined by the
actual measurement of its acting focal length and
diameter. But if it consist of two or three pairs of lenses,
not in contact with each other, this mode of measure-
ment will not give a correct result. The simplest and
best method in such cases, and indeed I may say in all
cases, is by means of the Microscope-gnomeometer, de-
scribed at page 218 of the Microscopic Cabinet.
Considering what has been just stated, I proposed, in
1835, that achromatic object-glasses should be applied to
the micrometer microscopes which were made use of for
reading off the divisions whilst making the trigonome-
trical survey of Ireland. They have since been used by
astronomers for similar purposes in the microscopes
attached to transit circles ; the advantage of which is, that
observations can be read off much longer in the twilight
of an evening without artificial illumination ; thus caus-
ing less fatigue to the eye than is experienced by looking
alternately at objects illuminated by different coloured
lights.
Lest it should be imagined that I have dwelt somewhat
too much upon the subject of angular aperture, I will ad-
duce a case in point to shew the necessity of its being
better understood than it is. I have in my possession at
42 MICROSCOPIC ILLUSTRATIONS.
this moment a triple object-glass, evidently made in
imitation of one of Mr. Tulley's achromatics. In con*
structing it, however, the optician, a person of great
respectability, was so unacquainted with what an achro-
matic is designed to effect, that he actually placed a stop
behind the lenses, so that, notwithstanding the focal
length does not exceed half an inch, an angle of aperture
of only 7 degrees is obtained. This object-glass of course
is inferior to a common lens : and hence has originated
the erroneous notion that the introduction of achromatics
has been no improvement to microscopes.
Should the question arise, why a single lens, or a com-
bination of convex ones, cannot be mounted so as to have
an angle of aperture equal to that in achromatics, the
answer is, that it can be done : I have often done it ; and
it affords an excellent method of shewing by comparison
the vast superiority of the latter over the former. Long
eXperience has taught the optician that common lenses,
when mounted in this manner, occasion such great aber-
rations that there is no possibility of obtaining any thing
approaching to a distinctness of vision. Hence has
arisen the necessity of placing a small stop behind them j
the effect of which being to transmit only a small pencil
of the light collected by the glass, the chromatism is re-
duced and rendered imperceptible. So effectually, indeed,
is this accomplished, that when one of our ablest philoso-
phers was told by Dr. Goring that he proposed to make the
object-glasses of microscopes achromatic, he exclaimed,
" I thought they had always been so constructed."
INTRODUCTORY RKMARKS. 43
The first effective achromatic object-glass for a micros-
cope was made, under the direction of Dr. Goring, by the
late Mr. W. Tulley, in 1824. It consisted of three lenses, a
concave inclosed within two convex ones. From its
great thickness, when compared with the ordinary object-
glass, it received the appellation of the thick* aplanatic
object-glass for diverging rays.
It appears that the celebrated Professor Amici, of
Florence, constructed some achromatics about the year
1815, but the happy discovery of test objects not being
then made, nor the value of angular aperture understood,
they were abandoned as useless at that period. In this
country Mr. Tulley went on improving the triple form he
had adopted ; and notwithstanding he found it extremely
difficult to work it on a small scale, and was thus obliged,
in order to get magnifying power, to have recourse to a
long body and a deep eye-piece, still he made the angle
of aperture as large as he well could. The foci of his
object-glasses were about 9-10ths of an inch, and
the angular aperture 18 degrees. Subsequently he in-
creased the angle to 38 degrees, by placing another
triple achromatic before it of 6-10ths, so that the acting
focus of the combination was only 3-8ths of an inch.
The objections to this arrangement are, that it is liable
to get out of adjustment — that it has twelve reflecting
surfaces, the lenses not being cemented together — and
that it cannot be worked of very short focus. It is con-
siderably easier to obtain any given angle of aperture
* See a section of it, drawn in plate 3 of the Micrographia.
44 MICROSCOPIC ILLUSTRATIONS.
with combinations of short foci than with shallow lenses ;
so much so, indeed, that 60 or 70 degrees with a focal
length of l-10th of an inch is gained with as great facility
as 20 degrees with an inch focus. Thus, in proportion
to the minuteness and delicacy of an object, the focus
must be shortened, if we would have a suitable penetra-
tion ; otherwise, the labour and time expended upon cor-
recting the pencils of light, more especially the oblique
ones, will be immense. The best proportions of angular
aperture to focal length are treated of in another part of
this work.
About the time of Dr. Goring's applying achromatics
to the microscope, M. Sellique, in France, invented and
executed a new description of object-glass, part of the
arrangement of which, on account of the many advantages
it possesses, is, and will probably continue to be, adhered
to by opticians. Its novelty and chief merit were, that it
consisted of several pairs of corrected lenses ; each pair
having a plano-concave of flint glass, and a double convex
of plate glass, cemented with mastic varnish. The latter
of these lenses was turned towards the object ; by reason
of which, as well as from the want of angular aperture,
the combination was not so effective as it was afterwards
rendered. The genius of M. Chevalier, of Paris, soon
led him to perceive some of these defects. He saw at
once that the plan of combining thin pairs of lenses
greatly diminished the chromatic dispersion, and he saw
also that the placing the convex lens next the object must
necessarily increase the aberration from sphericity. He
INTRODUCTORY REMARKS. 45
therefore mounted his glasses with the flat side of the
flint lens foremost, and he made the whole still more
valuable by the superiority of his workmanship. It was
not, however, until these object-glasses arrived in this
country, and their aperture was increased by Dr. Goring,
that their full effect was brought out.
In the early productions of M. Chevalier, the foci of
the different pairs of lenses composingan object-glass were
of unequal lengths ; the anterior pair having the shortest,
and the posterior the longest focus. Some of these sets
were admirably corrected ; and it is much to be regretted
that on account of the comparative difficulty there is in
this plan of constructing them, he should have been in-
duced to make the pairs of equal foci, by doing which the
maximum of angular aperture cannot be obtained together
with a fine definition. When we consider the errors which
are to be corrected in an object-glass, in order that it may
produce a magnified representation of an object suffi-
ciently perfect for it to undergo a second amplification by
the eye-piece ; and when we consider further that many
errors, which under ordinary circumstances are barely
appreciable, become very evident as soon as some prin-
cipal error is subdued, it is not surprising that the achro-
matic construction has been so long progressing towards
its present state of perfection. To say nothing of sphe-
rical and chromatic aberration, before mentioned, it is
no easy task to correct for the central and oblique pencils,
so as to obtain a moderately flat field ; the more especially
when we consider how restricted we are to certain forms
46 MICROSCOPIC ILLUSTRATIONS.
in our lenses, through the necessity of their being
cemented together to prevent loss of light. To say
nothing of the errors arising from the irrationality of
the spectrum — of the difficulty there is in centering and
adjusting the lenses — of the minuteness of the scale upon
which the whole is constructed, insomuch that the
slightest variation in the thickness of a lens (imperceptible
to the eye of a workman) is quite enough to alter the.
state of the aberrations in finely corrected object-glasses
of great angular aperture ; nay, that even the thickness
of the film of glass, or mica, used for the purpose of pre-
serving an object, may do this — it is not difficult to under-
stand that there have been great obstacles to surmount
in constructing an achromatic.
The talented Professor Amici, about the period of his
first attempt at achromatics, invented a reflecting micros-
cope. This instrument not having any chromatic disper-
sion to contend with, and only one surface to be figured,
was soon constructed with a considerable angle of aper-
ture. Hence its performance so far excelled that of any
other, that he was induced to lay aside his refracting
microscope at that time.
When an account of this microscope reached this
country, Dr. Goring, in 1824, suggested the idea of
working its concave ellipsoidal surface with a shorter
focus and a larger angle of aperture. Now, although
the working of a metal is in itself more difficult than the
forming a surface to a lens, yet the whole thing exhibited
so many facilities over the constructing of an achromatic
INTRODUCTORY REMARKS. 4/
lens, that a skilful artist found but comparatively little
difficulty in succeeding. For, look at the loss of time
which must of necessity be incurred in making trial of
an achromatic. Every time each lens has to be tried, it
must be removed from its holder, the cement cleared off,
and then placed in its setting; whereas a metal is
always ready; and there are no refractive or dispersive
powers to be ascertained, as with lenses, so that the
Amician reflecting microscopes were soon brought to
their most perfect condition. They have been made
with an angular aperture of 55 degrees, greatly surpassing
all the achromatics of that time.
The improved Amician microscope soon became a
decided favourite with amateurs, and had it not been that
considerable tact and experience were required, in
bringing out "its mettle," and that its range of effective
powers was limited, it would never, perhaps, have been
driven out of the field by our present achromatic micro-
scopes. I was soon convinced that of the three instru-
ments— the Jewel-doublet, the Amician reflector, and
the Achromatic — the latter would ultimately come into
general use. And entertaining this view of the subject,
I published, in conjunction with Dr. Goring, a very full
account of the method by which an artist may test the
value of his productions, and know whether or not he is
proceeding in the right path ; for I conceive that it is of
no trivial import to have the causes of defects pointed
out, when we desire to correct them. Since this publica-
tion in the Microscopic Cabinet, other artists besides the
48 : icroscopic illustrations.
late Mr. Tulley have succeeded in producing achromatic
object-glasses.
In the same work, the amateur is made acquainted
with a class of curiously organized bodies, which re-
quire a certain degree of perfection in a microscope to
render their structure visible, and thus enabled to exercise
a salutary check over the workman. Since this work
appeared, the achromatic microscope has been elevated
to such a pitch of excellence in this country that it stands
unrivalled throughout the world. We can now construct
object-glasses with angles of aperture of great extent,
and with the aberrations so accurately neutralized, that
hardly any thing remains but the colouring from the se-
condary spectrum, or that which is occasioned by the
irrationality of the dispersive powers of the different
media employed in their construction. It is not to be
expected that much more can be done ; unless, indeed,
other substances could be found for the making of lenses,
such as will obviate those defects, which it is impossible
for the workman to remedy with his present materials.
Many valuable and interesting additions to microscopic
science have been made from time to time by Sir David
Brewster; these should not be passed over without
proper notice; but since Sir David has so ably described
them himself, it is far more becoming in me to refer the
reader to his works, than to enter upon an explanation of
their merits in this place.
Our observations have been hitherto directed almost
exclusively to the optical portion of microscopes, and
INTRODUCTORY REMARKS. 40
more especially to the object-glasses of compounds ; eye-
pieces not having- been so much attended to of late, unless,
indeed, by Professor Airey and Mr Coddington. We must
not, however, omit to mention Dr. Goring's plan for con-
structing these of corrected lenses; an improvement
which has been carried into effect at Vienna.
A few words may be added on the subject of mounting
these instruments for use; a consideration of so much
importance, that, if it be not duly regarded, the most, per-
fect object-glass will be comparatively of little value.
I have seen many simple microscopes on stands so suit-
ably formed, that a great deal more might be done with
them, than with fme achromatics badly mounted. The
necessity of having convenient stands for microscopes
seems not to be much attended to, as yet, on the conti-
nent, theirs being seldom suited for more than one class
of observations. I would not be understood as disre-
garding the nicety of their workmanship ; on the contrary,
the beautiful finish they give to their productions is
hardly to be surpassed by us. As a large portion of this
work is devoted to the mechanical part of the microscope,
it is unnecessary for me to enlarge upon it here ; I may
observe, however, that since the publication of the first
edition, considerable attention has been bestowed upon
this subject, and that the principles herein laid down are
more or less adopted in the construction of all modern
instruments.
E
50
CHAPTER II.
On the Larva and Pupa of a Straw-coloured Plumed
Culex or Gnat.
Tipula cristallina of De Geer.
Chironomus plumicornis of Fabricius.
Corethra plumicornis of Stephens.
Transparency is a quality so essential to the display of
the internal organization of living- objects, that many
devoid of it are often disregarded, as of comparatively
little interest. The object now before us, however, is so
remarkably pervious to light, that under the microscope
we are enabled to view every part of its interior structure
with facility. Indeed, it is diaphanous in such a degree
as to render it difficult to be discovered in the waters in
which it resides, for it assimilates nearly in colour to
them, during the infant part of its larva state.
STRAW-COLOURED GNAT. 51
Had its pellucid nature been its only quality, as an
object for the microscope, it would have been worthy of
attention ; but it possesses others which render it a sub-
ject of the highest admiration to all who have seen it
under a good instrument.
This larva, which is produced from an egg deposited
by the perfect insect, inhabits still waters, and may be
found in canals and clear ponds which have a sandy or
gravelly bottom, but is seldom met with in places where
there is much herbage or water grass. In 1829, it was
found remarkably abundant in the small ponds in Epping
Forest ; and in the same year, a fine large variety was
met with near Killarney, in Ireland.
The most certain time to procure it is during the
months of May and June, though it may occasionally
be obtained on warm days in December and the other
winter months, provided the wind is not very high— a
circumstance which it is important to attend to, and
which will be again adverted to in our remarks on the
weather best suited for procuring aquatic insects.
The best method of obtaining this creature is by means
of a collecting net, made of linen cloth, which, after
a
being immersed in the water, near the e(\gc, must be
taken out, and its contents removed into a glass jar.
5*2 MICROSCOPIC ILLUSTRATIONS.
These must then be carefully examined by removing
small quantities at a time into a white saucer, or small
wide-mouthed phial. When they have been examined in
this vessel with a hand-magnifier, the objects sought for
should be removed to a store-jar, and the refuse thrown
away ; then inspect another portion, as before, until
all the water taken at a draught has undergone
examination.
Although nearly a quarter of an inch long in its
nascent state, this larva can scarcely be observed without
a hand-magnifier of about two or three inches focus
(unless the collector be short-sighted), as all its parts are
nearly colourless, except two pairs of kidney- shaped
bodies, which have a metallic appearance, and are nearly
opaque, as shewn in the plate at b, and d, in the mag-
nified side view, fig. 1.
The drawing, fig. 1, represents the creature in the
larva state. Fig. 2, shews the same being a day after-
wards, when it had changed to the pupa state. On com-
paring the two drawings, however, a very remarkable
and complete change of structure throughout will be
clearly perceived.
In the larva, fig. 1, the obvious and curious parts are
the kidney-shaped bodies b, and d, two of which are
situated near the head, and the other two in the third
division from the lower extremity. The first pair are
inclined towards each other, while the others lie in pa-
rallel planes, as represented in the plan, or bird's-eye
view, drawn of the natural size in fig. 3. Physiologists
have not ascertained what may be the functions performed
STRAW-COLOURED GNAT.
53
by these singular organs : it is worthy of remark,
however, that a similar structure is observable in the
tadpole, and figured in Sir Everard Home's Lectures on
Comparative Anatomy*. The other parts of its structure,
which appear equally singular and curious, are a number
of globules, a, which are situated near the first pair of
bodies, b. These globules have a slight oscillatory mo-
tion in different directions, and, like the reniform bo-
dies, seem to have a metallic lustre, but are not opaque.
From the exquisite polish of these globules, they reflect
the forms of surrounding objects, as window-bars, &c.
which are indicated in the drawing by small squares,
resembling the images formed by convex mirrors.
When the larva (as shewn of the full size in fig. 3) is
examined from above, it exhibits the position and decussa-
tion of the various muscles lying along the back, which
are observed to cross at the joints, and at points situated
midway between them.
The alimentary canal appears to contain some particles
of a pinkish coloured matter, and has a slight peristaltic
motion: but every part of the object, as seen beneath the
microscope, is so accurately noted in the drawing, that a
more minute description must be deemed supernuous.
If the insect have a sufficient supply of food, it only
continues for a few weeks in the larva state, when it ra-
pidly changes to the pupa, shewn in the drawing, fig. 2.
When it is desirable to preserve it for the microscope,
» Vol 6, Sup. Plate fjfi, fig I, ]),
54 MICROSCOPIC ILLUSTRATIONS.
this change may be retarded by keeping it in clear spring
or river water. The former seldom offers sustenance to
animalcules, and therefore effects this object; which is
often very desirable, on account of the scarcity of this
species.
The transformation of this animal from the larva to the
pupa is one of the most singular and wonderful changes
that can be conceived; and, under the microscope, pre-
sents to the admirer of nature a most curious and inte-
resting spectacle. Although the whole operation be
under the immediate inspection of the observer, yet so
complete is the change, that its former organization can
scarcely be recognized in its new state of existence.
If we now compare the different parts of the larva with
the pupa, we remark a very striking change in the tail,
which, in the previous state of being, was composed of
twenty-two beautifully plumed branches; while, in the
latter, it is converted into two fine membranous tissues,
ramified with numerous vessels. This change appears
the more remarkable, as not the slightest resemblance can
be discovered between them, nor are the vestiges of the
former tail readily found in the water. The partial dis-
appearance of the shell-like orreniform bodies is another
curious circumstance. The lower two, it may be con-
jectured, go to form the new tail ; for, if the number of
joints be counted from the head, the new tail will be
found appended to that joint which was nearest to them
in the larva state, as referred to by the dotted line d,
connecting figs. 1 and 2. The two small horns, c, c,
STRAW-COLOURED GNAT. 55
which form the white-plumed antennae of this species of
gnat, when in its perfect state, are discernible in the
larva, folded up under the skin near the head, at e, in
fig. 1. The alimentary canal appears nearly to vanish in
the pupa, as in that state there is no necessity for it, the
insect then entirely abstaining from food ; while, near
this canal, the two intertwined vessels, seen in the larva,
have now become more distinct, and are supplied with
several anastomosing branches.
During the latter part of the day on which the drawing,
fig. 2, was taken, the rudiments of the legs of the perfect
insect might be seen, folded within that part which ap-
pears to be the head of the pupa ; and several of the
globules had vanished, those remaining longest that were
situated nearest the head. It may be necessary to ob-
serve, that the head of the pupa floats just under the sur-
face of the water ; and the insect, in this state, is nearly
upright in that fluid ; while the larva swims with its body
in a horizontal position, or rests on its belly or sides, at
the bottom of the pond or vessel in which it is kept, the
fringed tail being downwards.
The circuitous manner in which the Creator appears to
produce this species of gnat, and many other of His
smaller creatures, is truly wonderful. Other beings are
produced directly, either from the egg or the maternal
womb. As, however, the Deity does nothing in vain, it may
be presumed that He must have had in view some impor-
tant object in the preliminary steps through which these
beings have to pass — from the eyy to the larva, crysalis,
MICROSCOPIC ILLUSTRATIONS.
and perfect insect; and, however low these minutiae of
nature may be held in the estimation of the unthinking
mass of mankind, this most elaborate proceeding renders
it not improbable that they may be deemed by Him choice
and exquisite productions. These mysterious operations
of nature, as detected and unravelled by microscopes, are
surely grand and capital subjects for observation.
I should pity the man who scorned to be amused by
inspecting these marvellous metamorphoses, and
disdained to be informed of the manner in which they
are effected. What a magnificent spectacle must such
a transformation present in the solar or gas achromatic
microscope, exhibited to a ivhole company with all the accu-
racy and fidelity ivhich the pictures formed by those instru-
ments are capable of displaying !
The colour of the larva when young is a faint and
scarcely perceptible yellow ; but as it approaches the
change, it assumes a richer and deeper colouring, and all
its internal parts acquire their definite forms and tints, as
exhibited in the drawing.
The natural history of this identical species of culex is
unknown, not having been noticed by any British writer
on entomology. The intense interest, however, which,
under the microscope, it excites in the observer, will
always render it an object of value. Other species of the
gnat are well known; and a description of the common
gnat, from the egg to the perfect insect, has been illus-
trated by Swammerdam, in his work entitled Biblia
Natures, sive Historia Insectorum* ; in which are two
* Tom. II. Tab. xxxi. et xxxii., \7.i7 , also Reaumur's Hist. Insect.
STRAW- COLOURED GNAT. [)~
foiio plates entirely devoted to it. This, however, is very-
different from the species exhibited in our drawings.
Indeed, the larva and pupa of the common gnat are too
opaque and uninteresting to be of much value as micro-
scopic objects, except in their transfiguration.
A curious circumstance attends the observation of this
insect : so rapid is its locomotion, that it torments the eye
while attempting to delineate it, presenting alternately
its head and tail to the observer. This it effects by bend-
ing itself laterally into a circular form, and suddenly
whisking round in the opposite direction to that in which
it had just bent itself.
In the dark ages of the world, when man considered it
beneath him to be watchful of, or attentive to, the work-
ings of Nature, and when superstition exercised an undue
bias over his mind, the new phases which a creature as-
sumed were conceived to be miraculous conversions, alto-
gether enveloped in mystery. Now-a-days, that his zeal
for investigation has led him on to a greatly extended
survey of Nature, and to a more minute acquaintance
with her operations than his ancestors were wont
to possess — not but that the ultimate causes to which
those operations are subservient remain as much a mys-
tery as they ever were — his pride and arrogance would
instigate him to get rid of every thing approaching to
difficulty in the whole routine of creation. He would
tell you that the metamorphoses we observe in insects,
like those we have been describing, by which a living
creature, an inhabitant of the water, whose life depends
58 MICROSCOPIC ILLUSTRATIONS.
upon its being immersed in that fluid, becomes a free
denizen of the air, incapacitated for a longer existence in
the former element, are of easy explanation : he would
tell you that the different transitions which the being has
to pass through, from the larva state to the condition of
the perfect fly, are but the semblance of a change ; for
that if you examine it just previous to the change, you
will discover the future fly folded up in the case of the
larva, and ready to issue forth when the covering is re-
moved. How badly this will serve for an explanation
of the whole phenomenon, and how little it detracts from
the greatness and the mystery of the change that has
been wrought, is sufficiently evident to every reflecting
mind : for, had the larva been examined in the early
state, not the slightest indications of the future fly would
have been traced. A gradual development of new forms
and new organs has been carried on under this old
covering, and an absorption of old forms and organs ;
which, however much it may seem at variance with the
antiquated notions of our ancestors as to there having
been an actual conversion of old matter into new, is not
a whit the less marvellous. The mere bursting forth of
the creature from its envelope is but a very small part of
the vast transaction.
Many species of this genus of insects are, in their
perfect state, possessed of a sheathed proboscis, con-
taining instruments with which they are enabled to
pierce the skin of men and cattle, injecting at the same
time an acrimonious fluid into the wound. The species
STRAW-COLOURED GNAT. ,r)9
we are now describing, however, has not been examined
minutely enough to determine the form of these organs.
It is of a light straw colour, and has two beautiful an-
tennae or feelers.
The wings, also, of this gnat are of a delicate straw
colour, and make very beautiful objects, when mounted
under thin glass in sliders. Some species have their
wings marginated, and covered with fine scales. These,
as well as the feathers on the edges, are good objects for
the microscope, and exhibit five or six longitudinal lines
on each, which are so strongly marked as to be seen with
any kind of light, and do not require superior penetration
in the instrument, to shew them. The whole wing may
be seen very beautifully under Goring's improved Amician
Engiscope*, with its lowest power, which is ecpiivalentto
a lens of a quarter of an inch focus. To the larva and
crysalis of insects this instrument cannot be applied satis-
factorily, as it does not take in the extent of field necessary
to shew the whole at once. On this account the achro-
matic microscope has the decided advantage, from the
low power and large area which can be obtained by it.
In examining this larva with the microscope, it will be
best seen when the light is thrown obliquely on it ; though,
when low powers are used, much attention to this parti-
cular is not required.
These insects generate while hovering in the air, and
the female lays her eggs in the water, selecting an unfre-
* Sec Micrographia, (hap. J.
60 MICROSCOPIC ILLUSTRATIONS.
(juented spot, where she may deposit them free from
danger. This is probably the cause why this larva is dis-
covered with so much difficulty ; the collector being
seldom able to procure it two seasons consecutively in the
same place.
The vignette at the head of this chapter was drawn
from a specimen bred in a vase. Whilst in the act of
producing the cluster of eggs figured on the right side,
I took and preserved it in gum. The eggs were removed
from the surface of the water on a slip of glass gently in-
troduced beneath them. These measure between the
one-fortieth and one-fiftieth of an inch in length.
The short line between the two figures indicates the
actual length of the body of the Tipuladian Gnat.
CHAPTER III.
On the Larva and Crysalis* of a Day Fly.
Ephemera marginata of Stephens.
When this larva issues from the egg, which it does in
the decline of summer, it has at intervals an unsteady
motion — in a manner, as it would seem, involuntary.
During this stage it is scarcely visible to the unassisted
eye, and is very pellucid. As it increases in size, the
serpentine vessels attached to the sides of the animal
become more apparent, and the tail assumes that rich
feathered appearance, which, in conjunction with the
paddles, form its pre-eminent beauty.
While the insect is very young, it is a well-suited
object for the solar achromatic microscope, in which it
will afford an ample fund of amusement, when repre-
sented on a screen, and dilated to the extent of about
two feet in length. If the instrument be truly aplanaiic,
every part of the insect's internal organization may be
clearly seen ; and the peristaltic motion of the intes-
tines, the circulation of the blood, and the pulsation of
the dorsal vessel, can be observed without the least
rouble, by any number of persons. In the latter circum-
stance the principal advantage of this instrument con-
* It may, perhaps, be termed either, according to its state of growth.
02 MICROSCOPIC ILLUSTRATIONS.
sists ; for it cannot be denied that an aplanatic compound
microscope will exhibit these appearances with more
distinctness, and without any risk of killing or injuring
the object by exposure to the heat of the sun's rays
condensed upon it.
As the creature continues growing, it assumes a va-
riety of colouring, and becomes more opaque as its
change approaches towards completion, which takes place
in a few months from the time it leaves the egg. The eyes
are reticulated, as represented in figure 4, plate 11, and
are of a citron colour 5 while the body exhibits a most
beautiful play of different tints, and finally assumes that
of a rich brown, with various shadings. The large
air-vessel (trachea)* which runs along each side of the
body, together with its numerous ramifications traversing
the different membranous leaf-shaped paddles, are now
of a dark colour, and the elytra, or wing-cases of the
future insect, become daily more and more apparent.
The magnified representation of the larva (fig. 4) was
taken just previous to its change to the perfect insect.
Fig 5. gives the real magnitude of the creature ; and
fig. 6 exhibits a view of the perfect insect of the natural
size.
During the infant state of this larva's existence it is
very transparent, displaying, under the microscope, in a
most surprising manner, the circulation of the blood.
The systems of respiration and circulation in insects
differ most materially from those of the vertebrated ani-
* The coat of this vessel differs from that of most larva, a fact not
noticed by naturalists.
EPHEMERA MARGINATA. 63
mals. In land animals the function of respiration is
performed by lungs ; in fish by gills : in both of which,
however, the blood is propelled to the respiratory organ
to be aerated. In insects, on the contrary, the air is con-
veyed through the body in vessels, called the tracheae,
and the blood is aerated by circulating around these
vessels ; whence originates the term, a diffused circula-
tion. In place of the heart is substituted a single pro-
pelling organ, which, from its peculiar situation, has been
named the dorsal vessel.
The circulation of the blood in this larva is shewn in
a magnificent manner in an achromatic microscope, with
a triple-cemented object-glass of an inch or half an inch
siderial focus. For this purpose I would recommend the
selecting of a young specimen about one or two-tenths
of an inch in length, when it has just shed its skin, at
which time the entire creature is exceedingly pellucid.
Around the large air-vessel which passes down each
side of the body, as also along the legs, antennae, and
three-forked tail, the oat-shaped globules of blood may
be seen to pass rapidly at every pulsation of the dorsal
vessel. This vessel, according to Mr. Bowerbank's ob-
servations*, " extends nearly the whole length of the
body, and is of great comparative magnitude. It is fur-
nished at regular intervals with double valves about
equal in number to the sections of the body." A portion
of this vessel, with its valves, is represented in the an-
nexed figure. " Both above and below each of these sets
* Entomological Magazine, vol. I, page 240.
64
MICROSCOPIC ILLUSTRATIONS.
of valves is a pair of singular- looking- appendages, a, a.
They are probably nervous ganglions, auxiliary to the
motion of the vessel, but so exceedingly pellucid as
scarcely to be defined. The action of the valves is a
most interesting and beautiful sight. While in their
greatest state of collapse, the point of the lower valve is
seen closely compressed within the upper one. At the
commencement of the expansion of the artery, the blood
is seen flowing in from the lateral apertures, (as shewn
by the arrows) and at the same time the stream in the
artery commences its ascent. When it has nearly
attained its greatest state of expansion, the sides of the
lower valve are forced upwards by the increasing flow
of the blood from the section below the valve, the lateral
openings are closed, and the main current of the blood
is projected through the two valves."
A portion of the larva of the Ephemera, greatly magnified, displaying the
structure of the Circulating System.
f< It is not easy to see this beautiful structure of the
valves of the great dorsal vessel, for it is only when the
insect is in a state of exhaustion, or has been just so
much compressed as to destroy voluntary motion without
entirely depriving it of life, that it is possible to subject it
EPHEMERA MARGIN AT A. 65
to a power sufficiently high to discern these extremely
delicate and transparent tissues; and even then, to see
them to the greatest advantage, recourse should be had
only to such as are in the last three or four sections of
the body."
When the larva is dead, the particles of the blood, of
an oblong figure, may be distinctly discerned in its forked
tail ; and their motion is perceptible in the limbs for
nearly an hour after they are separated from the body.
These particles, like those of the human blood, assume a
spherical form when mixed with water.
The peristaltic motion of the alimentary canal will also
present, under a good instrument, a beautiful and inte-
resting appearance.
The three-pronged tail of this insect, in its advanced
age, is beautifully fringed with clusters of fine, straight,
smooth hairs or bristles, several in each bunch, as re-
presented in fig. 4. As the time for its transformation
approaches, the central prong of the tail becomes more
transparent, and assumes the appearance of a jointed
tube, or shell-like case ; while the two exterior ones dis-
tinctly exhibit portions of the tail of the perfect insect
inclosed within them, as shewn in the drawing. The
same may be observed as to the legs, which are seen to
contain those of the perfect fly.
This larva is produced from an egg, deposited by the
perfect insect in the waters of pools or ditches, among
duck-weed and the water-grasses. Its disposition is mild
and inoffensive. It is incapable of destroying creatures
F
6G MICROSCOPIC ILLUSTRATIONS.
of its own size, while it is itself the prey of all kinds of
water-beetles and the larger larvae.
It feeds on the larvae of the smaller kinds of tipulae, or
crane flics, as well as on aquatic vegetables. Short
pieces of grass, &c. are frequently seen in the alimentary
canal, when examined under the microscope during the
spring season. For this reason, and also on account of
the sharpness of its claws, it should not be kept with any
of the family of the Characeae, intended to exhibit the cir-
culation (cyclosis) of the sap, inasmuch as it pierces the
cellules whilst creeping up the stems, and thus destroys
the plants.
When it is intended to collect this larva, a mild calm
day should be chosen ; for if there be any cold wind, it
retreats into the mud at the bottom of the water. It may
be easily taken with a collecting net, such as is described
in the preceding chapter. This must be introduced
among the grasses and water-plants to which they attach
themselves. Having carefully done this on that side the
pond which is most exposed to the sun's rays, and drawn
it among the floating duck-weed, many hundreds may
often be collected at a single draught.
These larvae may be kept alive, for many weeks to-
gether, in a glass vase of water, with a little duck-weed
floating on its surface ; and will be ready to be applied
to the microscope whenever required.
The rapidity with which it moves is truly astonishing.
Besides its six legs, it employs the six double paddles at-
tached diagonally to the serpentine vessels on each side of
EPHEMERA MARGINATA. G"
its body, and its tail, for the purpose of rowing and ba-
lancing itself, and two other paddles for steering, making
in all fourteen. Even when the creature is at rest, if in
health, all except the lowest two, or steering paddles, are
in rapid motion — a circumstance which renders those
beautiful ramifications of the air-vessels shewn in the
drawing, figure 4, difficult to be viewed while the larva
is alive.
Independent of its locomotion, by means of its legs, pad-
dles, and tail, it possesses a power of leaping or spring-
ing in the water, which it effects by incurvating its body
backwards, and then suddenly straightening it, by which
kind of motion it raises itself to the surface of the water
with great celerity.
When the crysalis approximates to its perfect state, it
swims more elegantly : its motions now appear entirely
subservient to its will, and at the same time it leaps with
greater velocity. Within a few days, however, of its
change, it becomes rather sluggish, and attaches itself to
the stalks of water-plants, on which it will remain for
hours together, if undisturbed, only moving its paddles
at intervals.
At the period of its transformation to the perfect state,
some parts of the insect assume a metallic lustre, as if
the space between the crysalis (which may now be called
the case of the animal, every part of the latter being
perceptible through it,) and the inclosed insect, were
partly filled with mercury. This appearance is ultimately
extended over the whole body, and is occasioned by a
G8 MICROSCOPIC ILLUSTRATIONS.
small quantity of air or gas probably evolved during- the
change ; and which, by insinuating itself between the
case and the insect, may facilitate the process. After
remaining a few minutes in this state, and making occa-
sional efforts to disentangle itself, it bursts forth from its
watery dwelling, and wings its flight into the aerial
regions, either leaving the entire skin behind it in the
water, or carrying part of it away.
The exuviae, or skins, which are shed previous to the
creature assuming the perfect form, are very fine trans-
parent objects for the single microscope, with a lens of
the tenth of an inch focus. In this state they afford much
useful information, as to the structure, formation, &c. of
which the paddles, tail, &c. furnish no inconsiderable
portion. If it be thought desirable to expedite the casting
of the exuviae, this may be effected by removing the
insect from the water in which it is found into spring
water. This change is most probably produced by the
water mechanically altering the dimensions of the skin
or case which inclosed the insect, and thereby suffering
it to escape with great ease ; or, perhaps, from the same
cause which produces this effect in the common spider
when deprived of sustenance. These skins should all be
mounted in sliders, in the order in which the insect sheds
them, that, by comparing them together under the
microscope, we may ascertain with precision the progress
made during each change.
When the crysalis is divested of its envelope, it remains
apparently inert on some neighbouring plant for a few
EPHEMERA MARGIN AT A. 69
minutes, where it casts off from its wings the last pel-
licle, which is a thin and delicate membrane, formed
under the elytra of the crysalis. It then appears in the
imago state, with its biforked tail and wings, as repre-
sented of the full-size in figure 6.
Having become a perfect Ephemera, it hovers about
in the air, the male and female generate, the latter drops
her eggs in the water, and both die, existing only a few
short hours, to perform all the offices destined for them
to fulfil in the economy of nature.
So beautiful and perfect are the arrangements of the
Creator, in order to preserve a regular succession of his
creatures, that if the Ephemeras be kept from sexual
intercourse, I have known them live for several days.
Nor do they seem enfeebled when confined separately for
a week, as I have seen them fly away with great celerity
after that interval ; while others, which were bred the
same season, and were not kept separate, died after a
few hours' existence.
70
CHAPTER IV.
Fig. 6.
Fig. 7.
On the Larva of a Species of British HydropJiilus.
Hydrophilus caraboides. — Auctorum.
In examining the peculiarities of the structure and habits
of this larva, what most strikingly attracts our attention
is its ferocious and savage disposition, and the fitness of
its organs for the exercise of its ravenous propensities.
It may be safely asserted that no species of larva is
known to be provided with weapons of destruction so
powerful, so numerous, and so well adapted to their end,
as those which this creature possesses. It is on this ac-
count that it has been popularly called the Watbr Devil.
Its size is but little inferior to that of the larva of any of
SPECIKS OF BRTTISH H VDROPHILUS. J\
the British Coleoptera, as it measures, when arrived at
maturity, an inch and a half in length, while the superior
strength and courage manifested in its attacks on small
fish, and other animals larger than itself, is truly sur-
prising.
About the latter end of April, and during the month of
May, small nests of these insects are often found floating
among weeds and water plants, in stagnant pools, and
are frequently taken in the nets of those who are search-
ing for the early kinds of larvae. They are in the form
of balls, of a dusky white colour, and a silky texture, and
have each a small stem of the same nature as the nest,
but more dense. By means of this filament they are
attached to the roots or stalks of weeds at the bottom of
the water. (See the right hand figure at the head of this
chapter.) In this situation they remain during the
winter, and are thus effectually preserved from the
effects of intense cold. Early in the spring, the stem or
cable to which we have referred is detached from the
weeds, by the winds which at that time prevail, and the
nest rises to the surface of the water, and there floating,
receives the genial influence of the sun. These nests
may be taken and placed in a basin of water, and, as the
season advances, hatched by the heat of the sun. On the
larva leaving the nest, which it accomplishes by gnawing
a hole in the side, the infant immediately descends to the
bottom of the vessel, with its jaws extended in search of
prey, and eagerly devours all the small aquatic insects
that are within its reach ; if, however, there is a scarcity
72 MICROSCOPIC ILLUSTRATIONS.
of food in the immediate neighbourhood of the nest, they
may be seen to attack and devour each other.
These larvae, as well as most of those of the larger
kind, are found at a greater depth of water than are the
smaller ones ; although, in their pursuit of small prey,
they may occasionally be taken in shallow places. They
require a larger net to collect them with. A net made of
stout Irish linen, about a yard deep, and affixed to a
hoop half a yard in diameter, will answer the purpose
very well ; and if it be attached to a long stick, the
collector will be enabled to use it with greater facility.
In its infant state, this larva is very transparent ; hence
its internal structure may be clearly distinguished.
When about a quarter of an inch in length, it swims
very nimbly. The colour of the head is a strong Indian
yellow, with darker shadings of a bright chestnut; the
eyes are now bright carmine. It is more sparingly
covered with hairs, and its swimming appendages are
shorter than at a more advanced period ; and the head is
larger, in proportion to the size of the body, than when
the creature has arrived at maturity. In this respect it
resembles many other creatures in its mode of growth,
the head seeming to be developed and perfected before
the rest of the system.
When young, it may be readily preserved in guni-
water, in the manner described in the " Microscopic
Cabinet," p. 229. I have several of them mounted in
this way, varying in size from one-tenth to half an inch
in length ; and although nearly eight years have elapsed
SPECIES OF BRITISH HYDROPHILUS. 73
since they were done, they are as perfect as when they
were first prepared. This method, however, will not
retain them so permanently as when they are mounted in
Canada balsam, between two slips of glass, in which case
the specimens may also be of much larger dimensions.
The manner in which this larva treats its prey evinces
an extraordinary degree of instinct. Many of the crea-
tures on which it feeds are crustaceous about the head
and back ; hence they are most vulnerable at the under
part of the body. This part, therefore, the larva attacks ;
and, to accomplish its aim, swims underneath the in-
tended victim, and bending back its head, which is even
with the surface of its back, is enabled thus to reach its
prey by means of its jointed antennae. (See a, fig. 30,
which represents a magnified view of the larva taken
while young.) Its next operation is to pierce it with the
mandibles (b). Having thus secured its object, it im-
mediately ascends to the top of the water, and, holding it
above the surface, so as to prevent it struggling, shakes
it as a dog would a rat. The prey of this larva is often
larger than its destroyer. Its next operation is to insert
the piercer and sucker (d), which is capable of being
thrust out or withdrawn at pleasure. When the juices of
the victim are not easily procured by suction or exhaus-
tion, the serrated pair of forceps (c), is employed to tear
and masticate it, and thus cause the juices to be more
easily obtained. If its food be plentiful, this larva arrives
at its full growth in the course of three or four months,
and is then nearly opaque, and covered with hair. It can
74 MICROSCOPIC ILLUSTRATIONS.
be kept several days without food, and by this exinani-
tion its structure becomes considerably more transpa-
rent*, while its natural ferocity is greatly increased, so
that it will attack and fight with creatures much larger
than itself, and even with its own species. It may be
remarked, that it studiously avoids any contest with the
Nepa, or water- scorpion.
On a fine sunny day the larvae rise to the surface of
the water, and delight to bask in the sun ; but if watched,
they remain motionless, with their claws extended. If a
stick, or any other substance, be presented to them, they
will immediately seize it, and will sometimes suffer them-
selves to be cut into pieces before they relinquish their
hold. Their bite has been considered poisonous by many
persons, as it takes a greater length of time to heal than
other wounds of the same extent : so that caution should
be used in taking them.
Touching the anatomy of this creature, it may be ob-
served, that the sucker, marked d, is contained in a crus-
taceous sheath, and may be considerably protruded or
completely withdrawn at the pleasure of the larva : in
the engraving it is shewn extended to about three
quarters of its length. The eyes are compound, but
of a peculiar formation, consisting of seven oval aper-
tures, arranged like leaves upon a branch : in the draw-
ing they are denoted by the letter e. The whole of the
* Dr. Goring kept the subject represented in the engraving some time
without food, in order to render its interior organization more clear : it
may be observed that its intestinal canal is quite empty.
SPECIES OF BRITISH II YDROPH I LUS. "5
head and thorax are curiously marked with a number of
lines and spots. The legs are six in number ; they are
thickly set with rows of hair on their opposite sides, and
each is furnished with a sharp claw. The number of
swimmers on each side is seven ; they are covered with
hairs, and, to the specimen from which the drawing was
taken, a vast number of Vorticellce convallarice,* or bell
polypi, were attached. These will be recognized in the
magnified drawing by their bell-shaped figure. They
sometimes infest this species of larva to such a degree, as
considerably to impede its motions in swimming. On
each side of the abdomen, which commences near the
origin of the first pair of swimmers, arise the great
tracheae, or air-vessels, distinguishable in the coloured
engraving by their light blue colour ; the two approach
each other near the tail, where an exceedingly curious
process is also distinctly exhibited. The whole surface of
the body is thickly covered with hairs, and several tufts
are disposed in clusters, with some regularity, down the
back and sides. The flexible pulsatory organ or dorsal
vessel, situated at the lower part of the body, is in perpe-
tual motion. Its form somewhat resembles the letter S,
inverted : it however varies a little during its vibrating
motions. The use of the curious appendages at the lower
extremity of the body is unknown. Its tail is biforked
and crustaceous, and is marked as shewn in the plate.
In figure 31 is given a representation of the larva, of its
* Described and figured in " Natural History of Animalcules," p. 149.
76 MICROSCOPIC ILLUSTRATIONS.
natural size and proportions, taken at the same period
of its growth as that at which the drawing was made. As
it approaches maturity, it casts its skin several times,
from each of which it escapes hy a rent formed down
the back.
The large tracheae, or air-vessels, which run along each
side of the body, with the numerous branches emanating
from them at various intervals, in their course, are com-
posed of delicate transparent membranes, distended by
means of fibres attached to, and wound about them in a
spiral form, like the thread of a screw or the spring
of a bell. The diameter of these vessels, one of which I
dissected from a larva nearly an inch and a half in length,
is one-sixteenth of an inch. When mounted between two
pieces of glass, and submitted to moderate amplification,
they exhibit the most beautiful and varied specimen of
line-work that it is possible to imagine. The fibres of
the upper and under sides intersecting each other at dif-
ferent angles, produce an effect which no engine-turner
could surpass; it would, therefore, be useless attempting
to illustrate it by a wood engraving. A branch of this
vessel may also be observed running along each of the
legs.
Respiration by this creature is not performed as with
the larva of the ephemera, although, like it, it is an inha-
bitant of the water. The tracheae in the latter is supplied
with air from the membranous paddles on each side of
the body, which imbibe it from the circumambient fluid.
In the larva under consideration, the air is supplied by
SPECIES OF BRITISH HVDROPHILUS. 'J'J
proper orifices situated at its tail ; and the creature is
obliged to ascend to the surface of the water, and elevate
its tail out of it, at every inspiration. When the air thus
inhaled has become unfit for respiration, it is expelled
at the same orifices, and a small bubble may frequently
be seen issuing from the tail, and ascending in the water.
On a careful examination of the skin, which by the by
affords an excellent object for the microscope, there will
not appear any spiraculas along the sides, as in perfect
insects.
The respiratory system of this larva, being, when dis-
sected out, more opaque than that of most similar crea-
tures, is seen to great advantage when mounted in
Canada balsam ; and if it be accompanied with the cor-
responding organs of a caterpillar, the comparison
affords a beautiful example of adaptation to the different
elements suited to life. In the terrestrial animal, every
part being exposed to the atmosphere, mouths or orifices
for inhaling the air are arranged along both sides of the
body ; in the aquatic larva, this system could not be made
available, without the creature being compelled to quit
its natural element, at every moment it had occasion to
respire. To obviate this, it is furnished with two large
apertures at the tail, instead of those at the sides.
I may mention that a preparation of this organ illus-
trates very beautifully one of the physical properties of
matter, namely, the colours produced by interference,
when light is made to pass between a series of fine lines.
After this creature has remained for a considerable
78 MICROSCOPIC ILLUSTRATIONS.
time in the larva state, it buries itself in a hole, which it
forms for that purpose near the edge of the water, and
after passing through the crysalis state, it emerges in the
form of a perfect beetle. This is effected in two years
after issuing from the nest egg.
On examining the older books on Entomology, I found,
in Roesal's work, (a book not noticed in Stephens' ela-
borate Catalogue of British Insects,) a small drawing of
this larva, from which it appears to be the Hydrophilus
caraboides. It is much to be regretted that modern
entomologists attend so little to the aquatic larvae of
insects ; for surely it will not be pretended that a
description of the creature in its perfect state constitutes
its history. I have often made inquiries of the first
entomologists of the day as to what insect a particular
larva would become, and have as often been unable to
obtain the slightest information. In some cases they
have doubted as to the order to which it belonged. It is
true that had I been unable to procure its generic and
specific names, that circumstance would not have ren-
dered it a whit less valuable as a microscopic object ;
and I do not pretend to treat of them with entomological
technicality.
The engraving of the perfect Beetle at the commence-
ment of this chapter is taken, by permission, from Mr.
Curtis's British Entomology, vol. iv., plate 159.
71
CHAPTER V.
On the Terms employed in Microscopic Science.
It has been said that every science has its own language,
and we often find that words which in one science ex-
press certain ideas, do, when transferred to another,
convey to our minds a sense entirely different.
Although the study of the microscope does not require
a very extensive vocabulary, yet it is rendered more
easy by a previous acquaintance with those terms which
continually occur to the microscopist.
The following chapters are mechanical descriptions of
the microscope, together with a discussion of the question
as to whether there is a best possible way of constructing
its mounting, or mechanical part. The importance of
the latter must be evident, when we consider that
although we may possess the most perfect and finest
corrected and adjusted lenses, yet if their mounting or
stand be defective in its construction, we shall be
deprived of a great portion of their value, by being
unable to make them show in an efficient manner those
subjects which are within the scope of the instrument,
while many classes of objects cannot be viewed by them
in any way whatever.
In the present chapter, I shall merely give a succinct
80
MICROSCOPIC ILLUSTRATIONS.
explanation of the different terms used in this and other
works respecting- the microscope, omitting Aplanatic ;
Achromatic ; Chromatic Aberration, or Dispersion ;
Spherical Aberration ; Engiscope and Microscope, as
being explained already in the u Cabinet," p. 102.
Fie. 8.
4*-
Fig. 9.
First, then, we will commence with the optical part
of a compound microscope, or engiscope, the external
appearance of which let fig. 8 represent. This is gene-
rally called the body of the microscope, and is either
composed of a conical or a parallel tube, as here shewn.
The interior of the body should be as black and as sombre
as possible, and furnished with diaphragms or stops (as
at e), to prevent any false light entering the eye: of
course these stops must be so arranged, and of such
apertures, at not to cut off or impede any portion of the
rays passing through the various lenses.
The larger end of the body, a, is called the eye-end, into
which the eye-pieces fit, either by a screw or simply
by sliding them within it. The latter plan is the better,
TERMS EMPLOYED. 81
though it has been objected to, from the liability of their
becoming loose by wear ; the reverse of which, however,
occurs in practice, for as the tubes become oxidized they
tighten.
The eye-pieces usually consist of two lenses, as shown
at a and b, fig-. 9. The first, or anterior lens, is called the
eye-glass ; the second, b, the jield-glass. As I have made
some eye-pieces of quartz, it would be more appro-
priate to call them eye-lens, or field lens.
The diaphragm, stop, or field-bar, is shown at c, and
should be in the focus of the eye-lens, a. The lens
which screws into the body at d, is called the object-
glass; it may be composed of more than one lens:
they are termed collectively objectives or object-glasses,
if they consist of three pairs, which is the usual
form for the best deep achromatics, as shown at fig.
Fig. 10. 10, where o is the place for the object (that
(\ ( W f] I being their combined acting focus) — d is
£ e d o the anterior or first pair of object-glasses —
e, the middle pair — and f, the third or posterior pair
of objectives. As the inner surfaces of each pair are
cemented together, to an ordinary observer they appear
as one lens, and consequently the objective appears to
be composed of only three lenses.
Over the object-lenses is often fitted a concave silver
reflector, for throwing condensed light on opaque objects ;
this is termed the LeiberkUhn, silver cap, or speculum, and
is shown at Plate 4, fig. 17-
The power of eye- pieces is determined by the focal
G
82
MICROSCOPIC ILLUSTRATIONS.
length and distance asunder of their component lenses, and
as they usually bear a certain relation to each other when
their construction is alike, their power is sufficiently dis-
tinguished by simply expressing the focus of the eye-lens.
Thus we say this is an inch eye-piece, meaning that the
sidereal focal length of the eye-lens is one inch. The
acting length of the body is the distance from the object-
glass d, to the diaphragm c (fig. 9), though it is usually
expressed by the length of the tube (fig. 8.)
I have been thus explicit, as the magnifying power
of an instrument is dependent on the focal length of
the objective, the power of the eye-piece, and length
of the body, taken together.
Fur. 11.
TERMS EMPLOYED. S3
The mechanical parts of a microscope I shall illustrate
by a reference to tig. 11, which exhibits the simplest
construction of a microscope with which 1 am acquainted.
It will be seen in the sequel to be the same as my achro-
matic engiscope, described in Chapter VI., but without
its apparatus and stand, which can be added at any time
by its possessor, and thus avoid the disadvantage usual
in the purchase of a cheap microscope, viz. that when
a better is required, the cheap one is too slight and
defective in its construction to form the basis of a supe-
rior instrument, and is, therefore, of necessity thrown
aside as useless.
The Vertical Microscope, fig. 4, consists of a double
arm, n, a ; the former to receive the screwed end of the
compound body, d, fig. 8 (when employed as an engi-
scope), and the latter, a, to receive the single, doublet,
or triplet magnifiers, when used only as a microscope.
b is a triangular bar, with a rack cut on its posterior
edge, into which a pinion works, which is actuated by
turning the large milled head, s, which raises or depresses
it and the arm, a, n, and thus the adjustment of the
focus is effected, j is the stage on which the objects to
be viewed are placed, and these latter are kept down by
the forked piece, or finger-springs, t. The mirror-socket,
m, slides upon the stem, c, and carries the mirror, o,
with its frame, p. Above the arm, a, n, is a milled head,
g, which serves to tighten it in any position in which it
may be placed : e is the circular foot or stand. When
intended as a travelling instrument, for lightness and
84 MICROSCOPIC ILLUSTRATIONS.
portability, the stem, c, screws into the top of the case,
and the round foot is not required.
As the above will be sufficient to explain the terms
used in the following chapter, I shall, to avoid repetition,
explain the remaining terms, when describing Dr.
Goring's and my own Engiscopes.
85
CHAPTER VI.
A description of the Achromatic Microscope, together with
its Apparatus and the mode of using it.
In a country like England, preeminently distinguished
for mechanical inventions, it would be strange, indeed,
if the constructing of stands for microscopes, their
mounting's, apparatus, &c. had not attracted the atten-
tion of some of her artists. Since the publication of the
first edition of this work, numerous contrivances of a
highly ingenious description have been devised for their
improvement ; and though many of them are too complex
ever to become of general utility, yet are they such on
the whole as have tended to advance this instrument to
its present effective condition. Several artists in France
and Germany have also especially directed their thoughts
to the microscope, and have produced some which, as
specimens of workmanship, claim, no doubt, very con-
siderable merit ; but they do not appear to have had
sufficiently in view the principles upon which they ought
to be constructed. Those which have fallen under my
notice are wholly unsuitcd for general purposes of ob-
servation— a circumstance which is the more surprising,
because there being exhibited so much talent in the op-
86 MICROSCOPIC ILLUSTRATIONS.
tical department, particularly in the eye-pieces, one
could hardly imagine that their usefulness would be
abridged through their inefficiency in other respects.
By a microscope suited for general observations, is to
be understood one of such construction as will allow us
to examine both opaque and transparent bodies with
such facility that we may ascertain their true forms and
structure. In order to compass this, both the instru-
ment and the illumination must admit of being turned
in all directions. The instrument must be further ca-
pable of carrying a wide range of magnifying powers,
so that whether the object to be investigated be of mo-
derate dimensions or a mere atom, it may come fully
within its scope. It is not an uncommon case to find a
microscope excellently constructed for a given power,
and totally unfitted for all others. For instance, that
beautiful little instrument for carrying Wollaston's
doublets, can only be employed with effect for viewing
very minute transparent tissues, as the scales of the
Podura, &c. It is not suited for examining the living
objects described in the previous chapters, nor most
animal or vegetable structures; and that splendid and
extensive class of bodies, opaque objects — which require
strong reflected light and moderate shallow powers to
render their beautiful structures appreciable — is entirely
beyond its reach. In either of the two microscopes I
shall describe in this work, every class of bodies that
I am acquainted with can be correctly judged of, whilst
they command a very extensive range of powers. Dr.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 8^
Goring's engiscope, described in Chap. VIII., being on a
much larger scale than that treated of in the present
one, is adapted for carrying the shallowest magnifiers
which can be required.
As these instruments have now become the standards
by which all the better kinds are made, modified more
or less so as to conform to the different views of the
artists who make them, I have judged it advisable to
treat of their several parts in detail ; in doing which
many of the remarks I shall have occasion to make, will
be found to have a general application. My own instru-
ment, with its various modifications and additions, to-
gether with their uses, will form the subject of this
chapter. In Chap. VIII. I shall give a mere explana-
tion of Dr. Goring's aplanatic engiscope ; the method
of making observations with, and managing it, being
penned by himself in the chapter following it.
The simplest modification of my achromatic micro-
scope is represented at page 82, fig. 11. This can be
used only in a vertical* position ; but it is admitted, I be-
lieve, to be superior to any instrument of that kind, in
steadiness, simplicity, and range of powers. It will be
readily conceived, that when the circular foot is un-
screwed, and the stem c, fitted into a jointed stand, it
becomes the second modification, shewn in the following
engraving, fig. 12.
This microscope is represented with its stem and axis
in an inclined position, which is commonly the most
convenient one for the observer. Those parts of it which
88
MICROSCOPIC ILLUSTRATIONS.
have been already described as belonging to the vertical
instrument, will be very briefly referred to here. Let
Fig. 12.
rip-. 13.
e, n, represent its compound body, which may be either
achromatic or periscopic ; its lower extremity screws
into the bent arm, n} whilst the other arm, a, is suited to
receive single or compound magnifiers. The stage, t,
on which the object-sliders are to be placed, is remova-
ble at pleasure. It is shewn separate by fig. 14. The
protruding ears on each side, shewn at, 4, serve to hold
by, when putting it on or removing it from the instru-
ment. These being in a line with the two stout pins
which fit into the block on the top of the stem, c, prevent
any strain being occasioned by the operation. This
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 89
being- attended to, and the triangular bar, b, sufficiently
raised, we may proceed with perfect safety. On the stage
is fitted, in a similar manner, by means of two smaller
pins, a fork-shaped plate of brass, shewn apart at fig. 13.
This plate is designed to retain the slider firmly on the
stage when the instrument is inclined. The focus is ad-
justed by means of a rack and pinion ; the letter, x9
denoting the large milled head of the latter. The
mirror-frame slides up and down the stem, c, thus allow-
ing the angle of the pencil of light to be increased or
diminished.
The stand of this instrument appears not to be different
from those of the old-fashioned compound microscope, ex-
cept in having a simple round foot, which is here adopted
to save room and expense. Like them it has a joint for in-
clining the instrument at any required angle ; but it has,
besides, this novelty, which, although simple, is of great
importance, viz. a capability of permitting the stem, c,
to be turned round on its axis, so as to allow a glass
vessel, or slider accommodated for animated creatures
or plants, to be retained in an upright position, and
their coutents investigated without having recourse to
stoppers or corks. When any of these vessels are used
in ordinarily constructed microscopes, they require to
be placed on their sides, which, independent of disturb-
ing the objects, admits not unfrcqiicntly into the field of
view, small portions of the air included in the vessels, so
as greatly to interrupt our view. When observations of
this nature are to be made, the stem, r, should be turned
90 MICROSCOPIC ILLUSTRATIONS.
a quarter round to the left, which brings the milled
head x, upwards, and the arm, n, a, horizontal, where
the stem, c, is fixed by the pinching screw, z. In this
position a candle may be placed close behind the stage in
the axis of the instrument. This will be found of great
advantage in verification. Again, if the stage be re-
moved, objects in glass vessels, which are too large to be
held in the microscope, may be examined without re-
moving them for the purpose; as also minerals, blocks
of fossil woods, &c.
The universal or ball-and-socket joint being strongly
recommended in Chap. VJL, it may with propriety be
asked, why I have introduced a different one into my own
instrument. The reason is, that while all the requisite
motions are obtained by means of the joint I have
adopted, it allows, at the same time, the stem of the
microscope to be over the centre of support, by which
it has no tendency to fall, when the pinching screw is
loosened. In the universal joint, there is always a
tendency to drop (except when it is on its side), and
a strain upon it. In practice, therefore, these are very
liable to get out of order, where the weight of the in-
strument is considerable. When formed on a small
scale, this objection vanishes; but when of the size
adopted by Dr. Goring, until a joint can be constructed
similar to that in the human arm, with a ligament in
the centre, and sufficient friction to support the weight
in any position, no person, I conceive, will give them the
preference : at least, so it has been ; for where one
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 91
microscope has been made with Dr. Goring's joint,
fifty have with mine.
Fii?. 15.
Fisr. 16.
Fig-. 15 represents a pair of forceps and a pin- holder,
attached to a ball-and socket joint ; the stem, c, fits into
holes formed in the stage to receive it. Opaque objects,
when mounted on a circular disc with a pin, are held
more firmly by the pin-holder (as seen by the figure) than
by the forceps. It is preferable, also, when the instru-
ment is on a small scale, to that ingenious contrivance in
Dr. Goring's Engiscope (see plate, fig. 23), as it admits
of the forceps being made smaller.
The arm, fig. 16, is used for carrying the forceps when
the stage is removed. The pin, b, fits into one of the holes
in the block of the instrument; and the pin, c, fig. 15,
into the hole, a. This arrangement for viewing opaque
objects allows large silver cups to be used, for conden-
sing the light upon them. Tliis could not be done, if
the stage did not take off, unless the aperture in it were
immoderately large.
The method of viewing1 opaque objects by means of
silver concave reflectors, is by far the simplest and the
readiest; and when these are of considerable diameter
and of proper curvature, we not only obtain the central
illumination, but also that beautiful play of light and
shade afforded by the oblique pencils.
For investigating insects, or other objects not mounted
92
MICROSCOPIC ILLUSTRATIONS.
on discs in this manner, an additional arm for carrying a
small black cup, to be placed behind the object, in lieu
of the disc, is extremely convenient.
Description of the Solid Tripod-stand Achromatic
Microscope and Engiscope. — This instrument, on its
simplest mounting1, is represented by the accompanying
engraving, fig. 1J. It is in all respects similar to the
preceding one, except in its stand. On this account
I have placed it in the position in which it is used for
Fig. 17
DESCRIPTION OF TUB ACHROMATIC MICROSCOPE. 03
viewing opaque objects by silver cups, where a is the
concave speculum, ovLeiberkuhn.
This stand differs from the other in the following par-
ticulars. The pillar is composed of a couple of tubes,
the one sliding within the other. The triple-milled
ring, q, screws upon the top of the outer one, and
serves to fix them together at any required elevation.
The base, u, u, u, consists of one solid piece of metal,
the form of which is that which several years' experience
has proved to be the best. Dr. Goring, in Chap. VII.,
clearly demonstrates that a tripod bearing is indispen-
sable to insure firmness. In his instrument, however,
the base, instead of being solid, is composed of three
pieces (see plate, fig. 7)> the objection to which is, that
notwithstanding a screw is used to counteract their
springing, the stand is yet liable to rock. I have lately
made some of his instruments with a solid base, similar
to my own, which are decidedly preferable.
My tripod form has been objected to, although the
solid base is now adopted in all the best instruments.
It has been said to occupy more room than those having
folding legs, and, therefore, to require a larger case ; and
again, that it should be equilateral, having its three feet
of equal length. The answer to this is, — first, that no
folding stand can be rendered perfectly firm, and that
there is some trouble and loss of time in arranging it for
use j and should it, through any hurry or mistake, be
set up without properly unfolding the feet, the instrument
is very liable to be injured. And, secondly, the base
94 MICROSCOPIC ILLUSTRATIONS.
here selected can be inclosed in a case no larger than is
necessary to contain all the other parts of the micro-
scope m3 and, with a given weight and dimensions, the
form is more steady than when the feet are of equal
length. Of course, to obtain the greatest advantage, the
stem, c, should always be over the shortest foot.
Having alluded to the packing of microscopes, it may
be mentioned, that upright cases or cabinets are greatly
superior to boxes for the purpose, because, the instant
the door is unlocked, the instrument is ready for use ;
besides, sufficient space is afforded for a nest of drawers,
to contain the apparatus and objects, although the latter,
perhaps, are better kept in a separate cabinet.
On the selection of proper Magnifying Powers. — In a
microscope constructed for single lenses, doublets, or
triplets, the plain split end of the arm, a, is the situation
designed to receive them. Upon examining the lenses,
such as possess the largest aperture are of the lowest
power. With these our observations should generally
begin. There should be marked, on them all, their
respective sidereal focal lengths. This measure will
indicate very nearly the distance at which they require
to be adjusted from the object. When the object to be
examined is a seed or large body, commence with either
of the three lowest powers. If the object is hardly
perceptible with the naked eye, take those of 1-1 Oth of
an inch focus, and so proceed, step by step, to the higher
powers.
Focal Lengths.
iuitgiiiivn
10-ii
Inches and Parts.
1
3-4ths
Diameters,
10
15
l-2nd
1 -3rd
20
30
]-4th ,
40
l-6th
60
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 95
Table of Magnifying Powers.
Magnifying powers, estimated by a
10-inch standard of sight.
100
225
400
900
1,600
3,600
MOth 100 10,000
Moth 150 22,500
l-20th 200 40,000
l-30th 300 90,000
l-40th 400 160,000
l-50th 500 250,000
l-60th 600 360,000
l-80th 800 640,000
l-100th 1,000 1,000,000
Previous to placing the magnifier into the arm just
mentioned, the triangular bar should be raised, the
object put upon the stage, and the light reflected from
the mirror made to pass through it. All this is more
readily effected before the lens is fixed in its position.
Some persons prefer having stops or diaphragms under
the stage, when making observations with single lenses.
In this case, the aperture of the magnifier may be greatly
increased ; for the stops, so situated, will have the same
effect of reducing the diameter of the emergent pencil of
light as a restricted aperture in the mounting of the lens
would do, whilst the vision for deep powers is rendered
by it more agreeable.
96 MICROSCOPIC ILLUSTRATIONS.
Whenever high powers are used, a safety slider-
holder, similar to that shewn by figs. 25 and 26 in
the plate, or fig. 20, page 106, should be chosen for
holding the object slide.
In the case of Engiscopes, or Compound Microscopes, the
arrangement for making observations will be different.
First, — the triangular bar is to be raised, and the bent
screwed arm brought over to the centre of the stage.
Then screw into it the body or tube. To the upper extre-
jnity fit an eye piece, of which, in a complete microscope,
there are several of different powers : the longest is
always the lowest power, and is marked A. Its angular
aperture, which determines the size of the field of view, is
generally less than that of the others (if constructed on the
Huyghean plan), being limited by the diameter of the
body. It is usually a little under 30 degrees. The next
eye-piece or middle power, marked B, and the deepest,
C, have more than 30 degrees of angular aperture. Their
amplifying powers are commonly in the proportions given
given below. It is not unusual, however, to have eye-
pieces of intermediate powers, to suit any particular
class of objects we desire to investigate.
Proportional Powers of Eye-pieces.
Names.
Diameters.
Surfaces.
A - -
. . 1
- - 1
B - -
. . 2
- - 4
C - -
- - 4 to 6 -
- - 16 to 36
For viewing thin sections of recent or fossil woods,
INSCRIPTION OF THE ACHROMATIC MlCROSCOl'K. 07
coal ; jet; the fructification of ferns and mosses; fossil
shells; seeds; small insects, or parts of large ones; molus-
cans, or entomostraceans; the circulation in the frog", &c.
the eye-piece, A, is best adapted.
Again, for examining the details of any of the above
objects, the eye-piece, B, should be substituted ; as also
for observing the colours of crystals illuminated by pola-
rized light ; the pollen of flowers ; the dissections of
insects ; the vascular and cellular tissues of plants ; ani-
malcules ; Haver's canals in sections of recent, and
the corpuscules, &c. in fossil bones ; the cyclosis in
plants ; the formation of shell ; the moveable fluids in
quartz and topaz ; the organic remains in thin slices of
flint, &c. ; the serrated lamina of the crystalline lenses
of the eyes of fishes and birds, &c. &c.
And lastly, when it is requisite to investigate either the
minutiae of opaque objects, or the minute structures of
delicate tissues, active molecules, polygastric infusoria,
and the raphides in the milky juice of plants, &c. the
eye-piece, C, comes into use ; it being oftentimes incon-
venient, when a higher power is needful, to obtain it by
means of a deeper object-glass, which occasions a fresh
arrangement to be made of the illumination and focus.
It must, however, always be borne in mind, that the
more powerful the eye-piece is, the more will the imper-
fections in the object-glass become apparent, because
they will be the more dilated. Hence we should observe,
that less confidence ought to be placed in the observa-
tions made under a powerful eye-piece, than when the
n
98 MICROSCOPIC ILLUSTRATIONS.
same amplification is obtained with a shallow one, and a
deeper object-glass : the preference, therefore, when
great accuracy is required, should always be given to the
latter arrangement wherever it is admissible.
An engiscope may be furnished with one or more sets
of object-glasses. They all have similar screws for fixing
them into the lower end of the body. When a set is
composed of only two or three lenses (the usual con-
struction of shallow ones), it can give but one magnify-
ing power. In like manner, when a set is constructed so
as to take up a very large pencil of rays with the utmost
definition, although composed of several pairs of lenses, it
can give but one perfect power. Such sets should never
be separated. In many cases, where a maximum angle
of aperture, or a perfect correction, can be dispensed
with, one set composed of three pairs of cemented lenses
may give by separation three different magnifying powers.
These sets are generally made so that their amplifica-
tions, in diameters, are in the ratio of one, two, and
three ; and are preferred by some observers.
Achromatic object-glasses for microscopes are of various
foci, differing from two inches to 1- 16th of an inch. As a
table of all the varieties would occupy more room than its
worth would justify my giving, I shall specify only those
which are mostly used in the table-microscope. They
afford a very wide range of powers, and one or the other of
them is suited for every class of objects which can be sub-
mitted for examination. It is seldom that an instrument
has the whole series attached to it ; and since many per-
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 09
sons confine their attention to a particular class of objects,
some little consideration is necessary for selecting those
sets which are best adapted to the purpose. It is by no
means an unfrequent occurrence, that applications are
made to me, by those who have purchased expensive
instruments, for some particular object-glass, which they
do not possess, whilst they have others which to them
are of little or no value.
The first column in the following table gives the side-
real focal length in inches and parts. This focal distance,
in shallow object-glasses, is less than the distance an
object should be placed at from the lens when adjusted
for distinct vision ; whereas, with the higher powers, the
sidereal focal distance is greater than that between the
object and the lens. It varies also with the length of the
body. The second column shews the distance at which
the object should be placed from the object-glass. The
third column gives the mean angle of aperture, which
varies a few degrees either way. The last column gives
the magnifying powers in diameters, in combination
with different eye-pieces. It is calculated by a 10-inch
standard for sight.
Sidereal Focal Distance between the Mean Angle of Magnifying
Length. Object and Lens. Aperture. Powers.
Inches. Inches. Degrees. Diameters.
2 . . ... 2, l-3rd 10° 20 to 50
1 1, l-8th 15° 30 to 120
l-2d 3 8ths 22° 65 to 280
l-4th l-8th 40° 150 to 500
l-8th l-20th 50° .... 260 to 1100
M6th .... 1.40th 70° 450to3000
100 MICROSCOPIC ILLUSTRATIONS.
The above sets may be divided into three classes — the
shallow, medium, and deep ; which, like the eye-pieces,
I shall particularize by the letters A, B, C.
The shallow object-glasses, A, are mainly serviceable
for opaque objects, which, when exhibited by means of
silver specula of proper dimensions and curvature, yield
a vast fund of amusement and instruction. The class of
objects, enumerated under the eye-piece, A, is suitable
for them. They display to great advantage, also, the
aquatic larvae of insects, polypi, &c. They are service-
able as a finder for minute objects ; for the general
examination and selection of insects; minute fossils;
coal, &c. ; the objects thus selected being afterwards sub-
mitted to the medium object-glasses, B.
Those denominated B, possessing considerable pene-
tration, bring out the striae and markings on the scales of
insects, the various forms of the elementary tissues and
fibres of vegetables, the internal structure of polypife-
rous zoophites ; whilst a general view of those minute
and delicate living creatures, the animalcula infusoria,
as also the circulation in the young of the lizard, aquatic
plants, &c, is obtained by the intermediate sets. The
medium-power object-glasses, when constructed with a
sufficient space in front, admit of a minute examination of
portions of insects preserved in Canada balsam between
plates of glass of the usual thickness. This class of
transparent objects, when mounted in the permanent
manner I have mentioned, is certainly the most instruc-
tive and amusing of any that we possess; for although
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 101
we cannot enjoy the sight of their motions and habits as
with living- specimens, yet are we in a measure recom-
pensed for it, by the advantage of having them always
at hand.
The object-glasses, C, are best adapted for investi-
gating objects of the most minute and delicate descrip-
tion ; such, for instance, as the markings on the scales of
the poduraj the forms and structure of minute fungi*5 ;
the globules of human blood, &c.
A variation of magnifying power is attainable also by the
body of the instrument being composed of two or more
tubes (see fig. 17,) the one sliding within the other, so as
to admit of an alteration of distance between the eye-piece
and object-glass : the power, in this case, will vary in the
direct proportion of the interval between the eye-piece
and object-glass. I am fully aware that this alteration
in the conjugate foci of the object-glass will affect its
corrections j still, in some cases, the advantages to be
derived from it will counterbalance this objection.
Having now given a description of the instrument in
its simplest mounting, together with examples for select-
ing its object glasses and eye pieces, I shall proceed to
consider, separately, the several additions which can be
made to it, inasmuch as each one of them can be em-
* Sec Rev. M. J. Berkeley's admirable paper on Fungi, Annals Sat.
Hist, vol. i. p. 82.
102 MICROSCOPIC ILLUSTRATIONS.
ployed in the microscope without reference being had to
any of the rest. By this means, persons engaged in parti-
cular investigations may easily judge of the peculiar appa-
ratus which is suited for them, and select accordingly.
Sect. 1. Candle- holder, Shade, and Condenser for the
Microscope. — The first addition to the mechanical portion
of a microscope we may consider to be the arm, k, repre-
sented at fig. 21, for carrying a candle or lamp, to
supply the requisite illumination. Those persons who
are in the habit of using an artificial light for the micro-
scope, are fully aware of the difficulties there are in con-
ducting their observations satisfactorily with it. Upon
all accounts, it is advisable that the candle or lamp-
holder should be attached to the stem of the microscope ;
for by this arrangement the light may be easily kept at
the required elevation, and the inconvenience arising
from the foot of the candlestick coming in contact with
the stand of the instrument, will be wholly avoided.
Besides, you will not experience the annoyance of being
continually obliged to alter the direction of the light,
through unconsciously moving about the microscope.
Having given in the " Micrographia," page 219, a
description of the above-mentioned apparatus, together
with the shade, and shewn it by several engravings, in
the following pages, at the positions, k, I, it is unneces-
sary for me to remark further upon it here. I may men-
tion, however, that the same rod which is used for the
purpose of regulating the illuminations, is made to
DESCRIPTION OK TDK ACHROMATIC MICROSCOPE. 103
carry the condenser also, and in a manner the most effi-
cient for concentrating the light upon both opaque and
transparent objects. The condenser is represented at
my in the same figures.
Sect. 2. Spring -double-Stage. — This stage, which is re-
presented at a, b, c, c, in fig. 24, is a vast improvement
upon the ordinary stages shewn in the previous en-
gravings, figs. 11, 12, and 17- It answers the purpose of
a safety-stage for large objects, mounted on a slip of glass,
or contained in a brass trough, or large live-box, which
must be placed between the stage-plate, «, b> and the
circular plate beneath it. This lower plate being kept
up by the two springs, c, c, allows the slider, trough, or
aquatic live-box, to be moved about in the manner re-
commended by Dr. Goring, in Chap. IX. The upper
plate, a, b, is furnished with a forked piece similar to that
shewn in figs. 13, 14, and has likewise a circular ring
for reducing its aperture when necessary. This stage
was contrived by me for making experiments with po-
larized light; for which I consider that it, or something
like it, is indispensably requisite.
It fits on to the microscope in the same way as do the
other stages, and like them may be furnished with dia-
phragms under it.
Sect. 3. Moveable Stage. — Various contrivances have
been made use of to give the stage of a microscope, when
an object is placed upon it for examination, a convenient
104 MICROSCOPIC ILLUSTRATIONS.
lateral motion. On Dr. Goring's principle, as described
in the next chapter, a corresponding effect is produced
by moving the optical portion of the instrument ; a
system which doubtless has its advantages, when either
the aquatic larvae of insects, or other large living objects,
are examined ; as also when any sizeable bodies are
being dissected under the regular microscopes employed
for that purpose. The moveable stage, however, for
small objects, and for general purposes, is usually pre-
ferred.
The ordinary method of adjusting a moveable or tra-
versing stage is by means of a couple of screws working
at right angles to each other ; by turning one or both of
which, a plate affixed to them, and carrying with it the
slider-holder containing the object, is moved in any di-
rection. Sometimes a screw and a rack and pinion are
substituted, by means of which all the movements are
effected on one side ; at others, levers are made to
answer the purpose. But by far the most elegant in-
vention is that of the late Mr. Tyrrel, the celebrated
mechanical engraver, which, together with some im-
provements 1 have made upon it, I propose to describe,
as being the one most likely to be adopted generally, and
preferred to all others. Its advantage consists in that
with one hand and without removing it, you can give to
the object a lateral movement in all directions. This is
done by attaching a screw to the lower fixed plate of the
stage, within whose axis passes the axis of a small
pinion, the outer extremity of each terminating in a
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 105
small milled head. These milled heads I place on the
same side as the large milled head, x, which works in the
rack of the triangular bar, so that all the motions are
obtained by one hand, whilst the other is left quite at
liberty.
Fig. 18.
In the annexed figure, 18, a plan of this stage is given.
It fits into the block of my instrument by means of two
pins, just in the same manner as the other stages, &c. are
made to do.
e, and/, are the two milled heads for effecting the
lateral motion. The former of these is connected with
the screw, and will move the stage to the right or left,
the latter to the pinion, and will move the stage to and
fro. By turning both the milled heads, therefore, at the
same time, a diagonal motion (by the composition of
forces) will be obtained, by which the object for inspec-
tion can be brought and retained in the axis of the in-
strument, y, y, arc two studs for the purpose of carrying
the arm d, at the further extremity of which a pair of
forceps (fig. 15) may be inserted for holding an insect, or
any other object which may be required. The studs
will support also a plate of glass when the instrument i>
106
MICROSCOPIC ILLUSTRATIONS.
in an inclined position, or the finger-springs, fig. 19,
which are suited to hold large aquatic live-boxes, &c. &e.
Fig. 19.
c
o
oD
An arm, c, is attached to the lower fixed plate, for car-
rying a small condensing lens, or reflector, for throwing
condensed light upon opaque bodies.
In Mr. Tyrrel's arrangement two sockets were fixed
in the front at x, x : the one for holding the condensing
lens, and the other the forceps, instead of the studs y, y,
and the arm c. The objections to this plan were, that
the condensing lens was moved together with the object,
so that the illuminated spot did not remain under the
centre of the instrument. The necessary consequence
was, that a re-adjustment was to be made at every move-
ment. Also, the situation of the sockets was such as to
obstruct large plates of glass containing thin sections of
fossil wood, &c. &c. from being laid upon the stage.
These inconveniences are entirely obviated in the im-
proved stage.
Fig. 20.
The upper plate or moveable part of the stage has a
circular aperture, b, furnished with two angular notches,
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 107
into which is fitted by a bayonet-joint the spring safety
slider-holder, fig. 20, or the finely-adjusting one de-
scribed in the Micrographia, page 217*
The utility of these safety-slider-holders is, that if by
any accident the object-glass should come in contact
with the slider containing the object when it is placed
between the plates, the object-glass will not be damaged;
for the spring which acts upon the lower plate will yield.
I most strongly recommend that a good object-glass of
deep power should never be used without this or a
similar contrivance. The numbers which are injured or
destroyed for want of this precaution are very great.
It is often quite impossible to restore them to their pri-
mitive excellence, even though the anterior lens of the
combination should not be broken. It may be remarked,
also, that in half the accidents of this kind which occur,
the observer is wholly unconscious of what has happened,
his attention being riveted to the object he is engaged
with.
Sect. 4. The Spring -Phial-Holder. — This apparatus is
designed to afford us all needful assistance towards inves-
tigating a certain class of objects without removing them
from their natural clement — fluids. The circulation or
cyclosis in plants, the circulation in the tail of a fish, the
structure and functions of various marine and fresh-
water zoophitcs, the habits of such entomostraccans and
infusoria as attach themselves to the sides of vessels, the
development of the young from the ova of creatures
108 MICROSCOPIC ILLUSTRATIONS.
which deposit them on the sides of vessels, &c. &c, fall
within the above description.
In examining any of these, this apparatus will be found
to be exceedingly convenient and useful} for, by its aid,
we can with perfect facility carry our researches into the
contents of any open vessels, or phials, of a size propor-
tionable to the range of the holder. In the ordinary way,
a phial or vessel, unless it be very shallow indeed, must
be turned upon its side, and stopped with a cork to pro-
vent the water from running out ; and even then it often
happens that a portion of the air included in the vessel
presents itself in the field of view, so as greatly to dis-
concert our plans. In using the spring-phial-holder,
however, this inconvenience is avoided : and there is,
besides, a more considerable advantage to be derived
from it, viz. that of not disturbing the objects, by turn-
ing them about, so as to accommodate them to the micro-
scope. Again, as open vessels can be put in the holder
with as much readiness as an ordinary slider can be placed
on a common stage, a series of observations on the con-
tents of different vesels may be made in a very short
space of time. In viewing by common means the cyclosis
in aquatic plants, such as those of the order Charace&y
where every cell throughout the plant has its distinct cir-
culation, it is necessary that a small portion of the plant
should be severed from the rest, placed in a slider, and
covered with a plate of mica or glass. This section will
not of course remain alive for any great length of time,
unless it be carefully replaced in a large vessel. With
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 109
the phial-holder the plant may be of a size sufficient to
live for months, during which it is ever ready for exami-
nation without any preparation whatever.
In a microscope of the common construction, if the
magnifier or object-glass should be accidentally brought
into contact with the object, when it is placed on the flip
of glass used for the purpose, it is very liable to be de-
stroyed. In this we perceive another advantage of the
phial-holder; for the spring, in this case, behind the
vessel, would yield, and thus prevent the injury.
Fig. 21.
Fig. 21 represents the microscope with the body e, n,
in a horizontal position. The stage is removed, and the
110
MICROSCOPIC ILLUSTRATIONS.
stem c, turned a quarter round, where it is firmly clasped
by the screw z. The body and arm, a, g, is drawn out
by turning the pinion-head s, so as to admit of the phial-
holder h, being" placed in its situation. This piece of
apparatus is shewn separately on a larger scale at fig. 22,
where p, p, are meant to represent the pins by which it
is attached to the microscope. Within the tube o, slides
another, s, which is propelled by a helical spring inserted
within it. This latter, or sliding-tube, has a thin con-
cave plate in front of it. When a phial, or other glass
vessel, similar to that shewn at fig. 23, is to be inserted
into the phial-holder, the tube s must be drawn back
towards o ; when liberated, the vessel will be firmly held
in any position.
Fi*. 22.
Fig. 23 illustrates the method by which an aquatic
plant is mounted, to exhibit the circulation. The plant
is carefully laid along the inside of the vessel, which is
empty. A slip of glass, a, is then covered over it, with suffi-
cient care to prevent it being injured. A small piece of
cork, b, is fitted behind it, and the vessel, then placed in
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. Ill
an upright manner, is filled with water. By this simple
contrivance, for which we stand indebted to Mr. Varley,
the plant is retained close against the interior surface of
the vessel, so as to admit of a magnifier of short focus
approaching it ; whilst in the space between the flat slip
of glass and the concave surface of the vessel, it will live
some months, without requiring any other attention than
merely adding a little water to replace that which shall
evaporate.
In reflecting upon what has been stated, it will be
evident that there are two points in the constructing of
our microscopes well worthy of notice, as tending to
facilitate the whole of this operation, viz. that the stage
be removeable, and the stem, c, capable of being turned
round.
When the phial-holder is mounted on a simple stand
for carrying only single magnifiers, it becomes a very
useful instrument for the above purposes ; as also for
the examination of the progress of crystallizations and
other chemical actions. In this mounting it is named
the Phial-Microscope; and as a mirror is not attached to
it, a lighted candle must be placed close to the end of
the tube, o, fig. 22.
Sect. 5. On the polarizing Microscope, or Apparatus
made use of for viewing objects by polarized light under
the Microscope. — Few subjects in experimental science
have roused the attention of philosophers of the present
age more than that of the polarization of light. Its
112 MICROSCOPIC ILLUSTRATIONS.
curious action on natural and artificial bodies, eliciting*,
as it does, a brilliancy of colours past all conception, lias
created so deep an interest in the minds not only of men
of science, but of all who have ever witnessed it, that a
treatise upon an instrument so intimately connected
with it as the microscope is, would, I am sure, be deemed
altogether incomplete, if it did not embrace some par-
ticulars respecting1 this great phenomenon. The trans-
mission of light through two thin plates of crystal is an
operation which can be readily enough understood ; but
that the mere turning of one of them a quarter round
should occasion a total stoppage of light, although the
thickness of the plates and their inclination to each other
remain the same, is so contrary to the general laws of
optics and to our daily experience, that we should be at
once disposed to question the fact, if we were not prac-
tically convinced of its truth. Again, supposing the
plates to be in the position last named, by which, as we
have said, the light is intercepted in its passage through
them, and it was suggested to us to interpose between
them an additional plate of a crystal, the natural conclu-
sion would be, that this arrangement would operate to
occasion a greater exclusion, if possible, than did the
other, which, under ordinary circumstances, would doubt-
less be the case. Having done this, however, we find,
to our great astonishment, that the light is now freely
transmitted, and often accompanied with the most in-
tense and splendid colouring. To arrange plates of
crystals in chaste and pretty designs, so as to make these
DESCRIPTION' OF THE ACHROMATIC MICROSCOPE. 1 \?>
beautiful effects visible to the natural sight, requires both
the talent of an artist and the experience of a workman.
Enlist, however, but the microscope into this interesting-
service, and the result will be that you will be supplied
at once, without a shade of difficulty, with an almost
endless variety of natural forms clothed in the most bril-
liant tints, and that too by the ordinary crystallization of
common salts. Thus, the application of a polarizing
apparatus to a microscope must be considered as being
highly desirable.
In a small pamphlet, entitled " A List of 2000 Micro-
scopic Objects," I have given a brief description of a
polarizer of my own contrivance, suggested to me
through being informed that Mr. Fox Talbot had applied
one to a compound microscope. To this gentleman is
due the merit of having first brought this arrangement
before the public ; as also the application to the engi-
scope of that beautiful invention of Mr. Nicol — the
single-image calc prism. It appears, however, that
Sir D. Brewster had for years attached tourmalines to
single magnifiers for the purpose of making experiments
on polarization by crystals. He did this by cement-
ing the tourmaline to a plano-convex lens, and then illu-
minating the object by polarized light reflected from a
glass or japanned surface*. Professor Amici, also, has
introduced the ordinary rhombs of Iceland spar into the
compound microscope for a similar purpose. lie has,
* Vide treatise on Microscopes, Encyclopfldia Britannica, p. 95.
/
114
MICROSCOPIC ILLUSTRATION*,
indeed, prosecuted the investigation of this subject by
means of the microscope, to a much greater extent than
any one else, by making it available towards exhibiting
the rings in plates of crystals cut across their axes, and
the exquisite tints in unannealed glass, &c.
Fig. 25.
S p C^
f2L P'
In these experiments I find that achromatic object-
glasses are almost essential ; for with common ones the
aperture is necessarily so reduced, that a sufficient
quantity of light will not be transmitted to give
intensity to the colouring. The object-glasses classed
under A, will be found most suitable ; and the eye-piece,
B, best constructed to take in the largest field admissible
by the prism.
Let i, fig. 25, represent the body of a compound micro-
scope, carefully placed over the centre of the spring-
double-stage, a, b. Let a slider of crystals be placed
upon the stage, a, b ; adjust to the focus, and illuminate
DESCRIPTION OF THE ACHROMATIC M IC ROSCOPK. 11")
witli as intense a light as can be made to pass through
them. Now, insert into the socket under the stage, at
e, a single-image prism, and then examine the crystals.
They will still retain their usual colour, if any, though
the light passed through them is polarized. This prism is
termed the polarizer.
Next, unscrew the cap of the eye- piece, P, and apply
another cap, containing a tourmaline, or single-image
prism. This latter is shewn separately at P'. By
turning one of the prisms gently round, it will be
noticed that in certain positions no more light will be
transmitted than just so much as passes directly through
the crystal; whilst the crystal, which, before the upper
prism or analyzer was added, was colourless, now dis-
plays the most brilliant colours. If a crystal be se-
lected exhibiting a deep orange tint, and the eye be fixed
upon it as the prism is turned a quarter round, the
colour will gradually change to green, and the light
will, at the same time, be freely transmitted through the
microscope ; in other words, the field of view will be-
come illuminated in the same manner as when a trans-
parent object is viewed in the ordinary way. Continue
turning the prism another quarter of a revolution, and
the light will again be stopped, and the crystal will
resume its rich orange tint. The two prisms are mounted
in brass tubes, with caps. The longer one is to be used
under the stage, as polarizer, and the shorter above, as
analyzer.
When the analyzer is a plate of tourmaline, instead of
116 MICROSCOPIC ILLUSTRATIONS.
Mr. Nicoi's single- image calcareous prism, a more
extended field of view will be obtained ; notwithstanding
which, the latter possesses many advantages over the
former, most especially that of its being colourless.
In cases where the ingenious invention of Mr. Nicol
cannot be procured, a rhomb of Iceland spar may be
well enough substituted, provided only that it has a
small aperture at the under surface, and that the upper
one is furnished with a sliding plate, with a correspond-
ing aperture, so that one or other of the images can be
seen at pleasure. Sir D. Brewster, who adopts this
method, cements a thin plate of glass upon both surfaces
of the rhomb, to take away their imperfections, and to
prevent accidents occurring, or deterioration of the
polish by cleaning.
The peculiar advantages resulting from the application
of the rhomb of Iceland spar, I shall give in Sir David's
own words. "These rhombs maybe made even out of
rhombs crossed with vt ins, which multiply the images,
because the multiplied images are at too great a distance
from the principal ones to be visible. This is a pecu-
liar advantage, as it is often very difficult to get good
pieces of spar free from this composite structure.
"This method of constructing a polarizing rhomb
enables us to take advantage of the two lateral images
which accompany the two principal images in crystals
crossed by on evein. These lateral images, shewn at
m, n, fig. 26, are distant from one another, and from the
principal images, b, c; and as each of them consists of
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 117
light wholly polarized in one plane, we have only to
bring" one of them under the aperture of the object-glass,
to have an admirable polarizer, without being at the
trouble of stopping out any of the other pencils.
"The images, mf n, are much less bright than the
principal ones, b, c ; but this is really of no consequence,
as we can obtain any degree of light we choose in the
microscope, either by the condensation of artificial, or
the use of solar light.
Fig 26.
m, b, c, n,
o o m
"When the vein by which these lateral images are
formed is above a certain thickness, their light is white ;
but they arc most frequently coloured ; and the observer
who understands the cause of these colours may make
this coloured pencil of great service in microscopical
observations. If he uses a rhomb, which gives to m a
green of the second order, it will contain none of the
extreme violet and blue rays, and none of the extreme
red ; so that it affords a more homogeneous pencil than
if it were white light, and thus improves the performance
of a microscope that is not achromatic.
" He may, in like manner, use tints which give (he
red extremity or the blue extremity of the spectrum, or
even, when the tint is divisible by the prism into perio-
dical bands, he may absorb the least luminous of these
band?, and create a homogeneous pencil of polarized
118 MICROSCOPIC ILLUSTRATIONS.
light, of inestimable value in particular researches, and
with particular microscopes.
" But, independent of these advantages, the method of
using a lateral pencil, m, has the great advantage of not
requiring any thickness in the rhomb. A Nicol's prism,
and a rhomb in which the two principal images, b, c, are
used, must be about an inch thick, in order to be effica-
cious ; but the distances, m, n, or m, b, are the same at
all thicknesses, so that Ave can use rhombs for this pur-
pose which are quite useless for any other.
u It is scarcely necessary to add, that similar rhombs in
which either the principal images, b, c, or the lateral ones,
m, n, are used, may be employed for the analyzer. For
this purpose, a thin plate, in which m, or n, is white, is
peculiarly applicable, as it enables us to see at once the
whole field of the microscope*."
In all the effects produced by the foregoing arrange-
ments, the field of view is either black or white. By
employing, however, the stage represented by fig. 25,
and inserting between the upper plate and the circular
one a plate of crystal or unannealed glass, the back
ground may, at pleasure, be made to assume a variety of
colours, so that the crystals shall appear like so many
coloured gems set in different tinted mountings ; whilst,
without this addition, they all seem to be set on black
velvet.
Considerable advantage is derived, also, from my con-
trivance of the double stage, in the examination of Mr.
* Treatise on Microscopes, p. 104.
DESCRIPTION OFTHK ACHROMATIC MICROSCOPE. Ill)
Talbot's " Analytic Crystals." As these experiments,
however, are full of interest, I have judged it advisable
to extract from the Philosophical Transactions, and give
entire, in the Appendix, Mr. Talbot's own papers upon
the subject.
If, in place of the upper prism, or analyzer, a double-
image prism be fixed at P, another and very beautiful
series of effects will result from the exchange. With this
modification there will at the same instant be seen two
images of the object arrayed in their complementary
colours ; and if we turn this prism round in the manner
before described, an interchange of colours will take
place between the images, the one assuming that of the
other. If long needle-shaped crystals are procured for
the purpose, the two images will be so far separated as
to appear quite distinct. They will vary in their positions
also, as well as in their colours -and intensity, while the
prism is being turned. A moon-shaped or crescent form
of complementary colours will be discernible on each
side of the field of view, while the latter will be white,
from the union of the two complementary colours. The
most gorgeous effect of all, however, is produced by this
double-image prism when a plate of quartz is inserted
below the crystals (say crystals of chlorate of potass)
placed at a, b. In short, the whole experiment is so
beautiful, that it is in vain to attempt any thing like a
description of it.
Some crystals possess the peculiar property of exhi-
biting two colours, when viewed by polarized light ;
120 MICROSCOPIC ILLUSTRATION?..
the one being elicited by the ordinary, and the other by the
extraordinary ray. Hence they are termed 'dichromatic.
To display dichroism in crystals, the lower prism, or pola-
rizer, should alone be used ; the eye-piece being allowed
to remain as when objects are viewed by common light.
If, whilst the dichromatic body is under examination, the
polarizing prism be turned a quarter round, the colour
will also be changed. In conducting these experiments,
the illumination need not be so intense. In large crystals,
dichroism may be readily seen without the aid of a micro-
scope, simply by placing them between the eye and a
japanned reflector inclined at the polarizing angle.
In order to convert the microscope into a complete
polariscope, I employ, instead of the mirror n, a pola^
rizing reflector, formed of several parallel plates of
thin glass fixed at the angle of polarization. A stage
must be constructed with a large condensing lens, and
made to slide upon the same stem, c, as is used for the
mirror. A double object-glass must be attached to the
body for obtaining a proper magnifying power, and the
analyzer should be made of tourmaline, in order to pro-
cure an expansive field of view. With this arrangement,
the phenomenon of polarized light, as exhibited in unan-
nealed glass, plates of amethyst, as also the coloured
rings and black crosses in crystals cut across their optical
axes, are seen in the most perfect manner. Professor
Amici was the first to exhibit these curious effects by
means of the microscope, although I do not know the
exact construction of his apparatus.
DESCIUPTION OF THK ACHROMATIC MICROSCOPE. 121
Sect. 6. Apparatus for dissecting. — Since the days of
Lyonet and Swammerdam, until of late, very little pro-
gress has been made towards producing a microscope of
a more complete description than their' s, for the purpose
of dissecting. It is true that two or three of this sort
have been constructed, but then they have been suited
for only one particular class of objects, such as the ele-
mentary tissues of plants, &c. Dr. Goring's engiscope,
with the additions hereafter mentioned as belonging to
myown microscope, probably approaches the nearest of
any to an efficient dissecting microscope ; nevertheless,
a still further advantage may be derived from having a
separate stand of proper dimensions made expressly for
the purpose. As one set of magnifiers will of course
suffice for both stands, the expense will not be consi-
derable. The microscope described in this chapter, with
the dissecting apparatus attached to it, is, I conceive, as
complete as any one of that size can be rendered ; its
dimensions however, are barely sufficient for the dis-
secting of large objects.
Having alluded to Swammerdam's microscope, it may
be advisable, I think, before describing my own appa-
ratus, to refer the reader to an account of his method of
proceeding (as given in the Appendix) ; containing, as
it does, many useful remarks. After the perusal of this,
and a brief description of Lyonet's dissecting micro-
scope, the reader will be fully prepared to understand
the construction I have adopted.
Lyonet's dissecting microscope may be thus de-
122
MICROSCOPIC ILLUSTRATIONS.
scribed : — It consisted of a circular brass table, in which
was cut a circular aperture half way between the centre
and the circumference. This table and aperture served
the purposes of an ordinary stage, and held a watch-
glass, trough, &c. to contain the object for dissection.
Under the aperture was placed the mirror ; and on the
opposite side to that where the aperture was made, was
inserted a socket, to which a number of universal joints,
strung together like a row of beads, were attached. On
the terminal one was placed the magnifier. Now fig. 27
Fiff. 27.
is a drawing of my instrument, placed in a vertical
position, as if intended for dissecting. Nos. 2, 3, represent
a wooden rest for supporting the hands ; this fits on to
the joint on the top of the pillar of the microscope, where
it is firmly retained. Near to each end, on the upper
surface of the rest, is a deepened or hollow place to pre-
DESCRIPTION OF THE ACHROMATIC MICAOACOPE. 123
vent the hands from slipping. It will be observed, that
the rest here given is perfectly straight ; notwithstand-
ing, in some cases, it will be more convenient to have it
of a semicircular or curved form. There is an arm, a,
which slides in a socket attached to an universal joint.
This arm has a spring ring for carrying the magnifiers,
which are inserted into it in the same manner as into
the plain end of the arm, shewn in several previous
figures. The dissecting trough, #, is placed in the
moveable stage in the way described in " Micrographia,"
page 215. This trough, which contains the object to be
operated upon, is capable of being turned about in any
direction. When the object is opaque, the condensing
lens, m, shewn in figs. 29, 30, must be brought into the
position, A, to concentrate the light upon it.
Single or doublet magnifiers are commonly preferred
to the compound microscope for dissecting, because the
latter instrument inverts the image of the object. The
amplifying powers, which are most generally service-
able, are those from an inch-and-a-half focus to the one-
tenth of an inch. When higher powers are requisite,
the lenses should be made of jewels, as they allow d
more space between the object and the lens than do
glass ones.
The advantages which I conceive this arrangement
possesses over others, arc as follow : — In the first place,
the rest or support, being made of wood, does not con-
duct the heat away from the hands so freely as if it were
of metal. 2dly. It being situated over the central sup-
124 MICROSCOPIC ILLUSTRATIONS.
port of the instrument, and being independant of it, all
straining upon the microscope is avoided, and the stage
may be inclined without disturbing the hands. This
will be found to have a two-fold advantage ; for, by in-
clining the instrument, the operator is placed more at
his ease ; and the superfluous matter can be easily drained
away, which is necessary when large insects are being
dissected. For dissecting these objects, thin pieces of
soft wood, having brass rings cemented to their under
sides, and being fitted into the moveable or other stage,
will be found extremely convenient.
The integuments of these creatures, as soon as they
are laid open, should be pinned down upon the wood,
while the nervous, respiratory, or alimentary organs
are being removed. The fatty matter, so very abundant
in insects, must be washed away with a camel-hair
pencil. By forming a ledge round the wood with a
little wax, the creature may be dissected under water
or diluted spirits.
The arm, a, having an universal joint, may be turned
about in any direction ; and should any remarkable
feature present itself whilst dissecting, which it is de-
sirable to examine without removing it, this may be
readily effected by taking off the screw-nut, #, and substi-
tuting the usual arm of the microscope, with the achro-
matic body.
Sometimes the achromatic body is employed in making
dissections ; in this case, the image being inverted, it
requires some practice in using the dissecting instru-
DESCRIPTION OF THE ACHROMATIC MTCROSCOPU. 125
merits, unless an erecting eye-piece is applied, as men-
tioned in the following chapters.
Sect. 7- Single Lenses mounted in imitation of Achro-
matic Object-glasses. — A series of single lenses mounted
as object-glasses, and of the same foci and angular
aperture as achromatics, will prove an excellent
method of instituting a comparison between their relative
values. The object-glasses are the most costly portion
of an achromatic microscope, notwithstanding to ordi-
nary observers they appear not to differ exteriorly from
common lenses mounted in the manner described. Some
persons are very apt to imagine that the additional price
of the one above the other is owing to the achromatics
superior magnifying power ; but as this does not
necessarily follow, these single lenses will manifest at once
wherein the superiority consists.
By way of trial, screw to the body of the microscope
one of the single lenses ; place an object under it, and
examine it with attention : then remove the single
lens, and substitute an achromatic object-glass in its
stead, allowing the object, eye-piece, and other portions
of the instrument, to remain as before. The difference
will be apparent enough in a few minutes to leave a full
and lasting impression upon the mind, of the extensive
improvement which has of late years taken place in this
respect. I know of no better mode than this by which
persons unacquainted with optical science can judge
fairlv of what has been eftected for the microscope.
126 MICROSCOPIC ILLUSTRATIONS.
The achromatic will be distinguishable from the single
lens by its exceeding penetration, and by the total free-
dom from spherical and chromatic aberration with
which the light is transmitted through it. It is true
that if the common lens have a diaphragm to limit its
aperture, the vision will be more distinct, and the light
less coloured ; but then, compare the two again, and in
the case of the single lens there will be a perceptible
diminution of light, and the eye will soon grow weary in
endeavouring to trace out the minutiae of an object.
Sect. 8. Garden Clamp for the Microscope. — This piece
of apparatus enables us to employ the microscope for
the examination of flowers and plants in the garden or
greenhouse. The clamp is represented by the annexed
engraving, fig. 28. The end, c, may be screwed to a
Fig. 28.
tree, door-frame, or any other convenient place. The
body of the microscope is then inserted into it at a, and
fixed there by the pinching screw, b. To the lower end
of the body is screwed a small arm, constructed for the
purpose, and carrying the forceps for holding the object.
The object-glasses, A, with their silver specula, are the
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 127
most serviceable for this occupation, as the adjustment is
very readily made with them. The microscope, suitably
equipped, may be used for examining flowers without
either its stand and apparatus, or the clamp : the body,
with the arm above mentioned, being merely held
in the hand. A variation in the magnifying power is
obtained by sliding the body in and out, and thus avoids
the necessity of changing the object-glasses, which,
out of doors, would be attended with some risk of loosing
them.
Sect. 9. Steadying Rods. — When we have recourse to
very high powers for making microscopic observations,
it is of consequence that the microscope be kept as
steady as possible, all motion, or tremor, being magnified
to the same extent as the object itself. Under such cir-
cumstances, it is often expedient to have one or two
sliding rods, whose upper extremities may be attached to
the eye- end of the body, and their lower to the feet or
pillar of the stand. When these rods are employed, all
their tightening screws must remain loose until the
instrument is set in the proper position — the moveable
stage, with its fine adjustment, put on, and the object-
glass, selected and adjusted to distinct vision by means
of the rack and pinion, in the usual way. When this ia
effected, the steadying rods may be clamped tight with
the pinching screws, and all subsequent adjustment to
distinct vision made by the fine adjustment, the rack and
pinion being nowT considered immoveable.
128 MICROSCOPIC ILLUSTRATION'S.
Although this contrivance sufficiently obviates the an-
noyance occasioned by tremor, yet I strongly recommend
a small stout stand being had expressly for the purpose ;
the additional expense not being great, whilst, from
its simplicity and convenience, you will be amply
recompensed.
Another purpose to which the steadying rods may be
applied, is that of drawing with the camera lucida. In
this case, the body of the microscope should first be
ranged horizontally, the steadying rods tightened with
the clamping screws, and then the requisite adjustments
made, the body remaining a fixture.
Sect. 10. Camera Lucida for drawing with the Micro-
scope.— This instrument is constructed in a variety of
ways, but the most serviceable is that shewn in the plate,
fig. 12. As there is only one reflection, the image of the
object is presented to you with its sides reversed, re-
sembling a copper-plate engraving from which the im-
pression is taken. The method of using this instrument
is as follows : — With my microscope, the cap, or cover,
which limits the pencil emerging from the eye-piece,
must be unscrewed, and the ring, to which the camera is
attached, substituted in its stead. This ring is furnished
with a pin for the camera prism to slide upon, which
may thus be made to approach or recede from the eye-
lens to suit the emergent pencils of light. The inclina-
tion is regulated by turning it on its axis.
For making drawings of microscopic objects, the eye-
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 120
piece may be conveniently removed from the body of the
microscope, and the end covered with a cap, having a
plate of finely ground or greyed glass fitted into it. On
this plate the image of the object will be formed, and
distinct vision obtained by adjusting the focus in the
usual manner. In this case, the eye-end of the micro-
scope, in order to produce the desired effect, must be
kept darker than the other extremity. If, instead of the
plate of glass, a piece of tracing paper be employed, the
image may be delineated at once. Also, the glass may
have divisions marked upon it similar to those in the
plate, fig. 13, and be used with drawing paper traversed
with squares, on Mr. Bauer's plan, described in the
Micrographia.
One great advantage which the camera lucida derives,
from its connexion with the telescope or microscope, is,
that the reflected image is thrown on the drawing paper,
so as to appear in the same plane with it. When it is
used without either of these instruments, the image
is formed at the same distance below it as the object is
distant from it in front ; thus occasioning an error by
parallax with the image and pencil, upon the slightest
motion of the eye.
Beginners in drawing experience some difficulty in
obtaining a distinct view of the point of the pencil simul-
taneously with the magnified image. The Rev. J. B.
Reade informs me, that by illuminating the object with
strong lamp-light in the day-time, and the paper on
K
]30 MICROSCOPIC ILLUSTRATIONS.
which the tracing is made with day-light, this inconve-
nience is entirely remedied.
Sect. 11. Micrometer Eye-pieces.— The micrometer eye-
piece is made to slide into the body of the microscope,
like the ordinary eye-pieces. This eye-piece is designed
either for drawing or measurement. When we employ
it for drawing, a plate of glass, with divisions similar to
those represented in the plate, fig. 13, must be used, in
the manner described by Mr. Bauer. When for mea-
surement, a slip of pearl, with divisions of 100 or 200
to an inch, answers best for all practical purposes. It
must be remarked, however, that the same divisions re-
present different measurements according to the power
of the object-glass and length of the body. When, there-
fore, they are once ascertained by the rules laid down
in the Micrographia, page 48, they must not be altered.
For either of the above purposes, the micrometer must
be placed at c, page 80; in the focus of the eye-lens, a.
Now as the distance of distinct vision differs in different
persons, and even in the same person, according to his
state of health, the adjustment must be made so as to vary
the distance bet veen a and c. This is ordinarily done
by moving the lens ft, with a screw. On consideration,
however, it is evident that by this means the achromatism
of the eye-piece is disturbed. I have obviated this defect
with my eye-pieces by giving the adjustment to the
field-bar, c, which carries the micrometer.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 131
Sect. 12. Method of viewing moveable Fluids in the Ca-
vities of Topaz ', Quartz, and other Crystals. — The existence
of small cavities in crystals is of such frequent occur-
rence, that few persons who are in the habit of seeing
crystals at all, can be unacquainted with the fact.
That some of these cavities, however, contain moveable
fluids, is a recent discovery, for which we stand indebted
to Sir D. Brewster. As I am not aware that the method
of observing these under the microscope has ever been
explained, a few words upon this subject may not be
considered superfluous.
Let your microscope be placed in a vertical position ;
apply a power of 100 or 200 diameters, and put the
crystal for examination upon the stage. Bring one of
these cavities into the centre of the field, and adjust to
distinct vision, when the fluid will be discerned within
the cavity, resembling an air-bubble. The proof that
this appearance is occasioned by a fluid contained within
the crystal is very readily ascertained. Take a metal-
heater of a proper size, having a hole in the middle to
allow the light to pass through ; warm it, and hold it by
its handle under the aperture in the stage, close behind
the glass plate upon which the crystal is situated.
During this operation you will observe the fluid in
the cavity expand, and, in some cases, become vola-
tilized ; and then, upon cooling again, return to its fluid
condition.
Many of the cavities in gems, particularly in the
132 MICROSCOPIC ILLUSTRATIONS.
diamond and garnet, are perfectly spherical ; and, owing
to the great refractive power of these stones, they have
the appearance of hlack and opaque globules with a
small bright spot of light in their centres. The propor-
tion between the diameters of the dark annulus and the
luminous spot, Sir D.Brewster has ingeniously proposed
as a measure of the refractive powers of both the solid
and the fluid. He has suggested, also, that these cavities
being permanent, arc preferable to Dr. Goring's* air
bubbles in Canada balsam, for determining the aberra-
tions of object-glasses ; but a little consideration, I
think, will suffice to shew that both the one and the
other of these tests must give erroneous results for
ordinary objects. And for this simple reason, because
the light coming from the cavity to the object-glass*
through a portion of the gem, will be refracted by it,
and enter the object-glass in a different state to what
it would have done had no such medium intervened
between the cavity and the lens.
In examining the organic remains embedded in flint,
the object-glass requires to be corrected by this test, as
the rays of light proceeding from the creatures dis-
coverable in thin plates of that substance, have to pass
through it before they enter the object-glass. The
recent discovery of the crystatella f and other infusoria
in flint, as also the sporules of ferns, has opened an en-
* See Micrographia, page 107.
•f Zantliydium furrata of E.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 133
tirely new field to the geologist, and one which promises
some very important results in throwing light upon the
original formation of that stone. Some beds of flints are
crowded with these infusoria, whilst others are wholly
without them. In viewing' these creatures (crystatella)
a powerful object-glass is requisite ; and, as their
multi-pronged spines protrude from all parts of the
surface of their bodies, each part being in a different
plane, there must be a new adjustment of the focus.
Some of the cavities in minerals contain '' two fluids
unknown to the chemist : groups of crystals, floating'
balls, &c" The forms of these cavities are various.
Those containing two fluids, which do not mix though
in the same cavity, appear globular.
Sect. 13. Concave Specula, Silver Caps, or Leiberkuhns,
for illuminating opaque objects. — In viewing opaque
bodies by means of concave specula, it is generally
advisable to remove the stage of the instrument, and to
insert the arm, fig. 1G, with the forceps, fig. 15. An
object-glass of a right focus must then be screwed into
the body of the microscope, and the silver cup, properly
fitted, made to slide over it. If candle-light, which is
the simplest artificial illumination, be used, although a
small argand lamp is often preferable, the light may be
placed from about 3 to (5 inches behind the object.
When we have day- light, the concave mirror must
be brought into the rear of the object. In this ease it
134 MICROSCOPIC ILLUSTRATIONS.
should be placed as near to it as it conveniently caii
be, in order that the cone of rays reflected from the
mirror may spread over the whole surface of the silver
cup; otherwise, the maximum illumination will not be
obtained.
Having brought the object into focus, the silver cup
must be adjusted, without altering the adjustment of the
focus of the instrument. This is done by sliding the tube
belonging to the silver cup over the tube which is screwed
before the object-glass. In order to obtain the maximum
quantity of light, the cup must be placed so that the
object is a little within its focus. As the length of this
focus, however, varies with the distance at which the
candle, lamp, or other illuminating source is placed from
the cup (the rays being thus either parallel, diverging,
or converging,) the adjustment must be made after the
position of the illuminator is determined upon. Thus,
when the cup is used with a candle placed at 3 or 4
inches distance from it, the rays being divergent, the
focus will be elongated, in which case the two tubes
must be thrust in. Again, when we illumine by day-
light reflected from a plane mirror, the focus is shortened,
and the outer tube requires to be drawn out a little.
In the old constructed microscopes, the concave spe-
culum, or silver cup, was attached to the stage of the
instrument, so that a fresh adjustment was always re-
quired for every change of object. By the above men-
tioned plan, as soon as the cup and light are adjusted,
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 135
nothing- further is necessary in this respect; for when
the object is brought into the focus of the microscope, the
illumination is sure to be correct.
Persons who have never viewed opaque objects with
shallow or medium power object-glasses, and silver
cups of proper diameters and curvature, are not aware
of half the beautiful effects resulting from the achromatic
construction. And as for objects that are suited to this
method of illumination, they are almost infinite in num-
ber; and, consequently, a greater fund of instruction and
pleasure is derivable from it than can be obtained with
deeper powers, where the objects which can afford
amusement are much more limited.
Sect. 14. Stops or Diaphragms are used for the purpose
of limiting the illuminating pencil of light, and may be
described as being small tubes with apertures at each of
their extremities. These are made to slide into sockets,
which screw into orifices formed to receive them at the
under side of each of the stages of the microscope.
They are sometimes furnished with a wheel of apertures,
similar to that shewn in the plate, fig. 24 ; and some-
times these sliding tubes have a small condensing lens,
such as that exhibited in the Microscopic Cabinet, page
1J0. By having the stops or diaphragms in the form of
tubes, the effect they are designed to produce may be
varied, if necessary, by sliding them up and down within
their sockets. Those possessing the lens, and intended
to act on Dr. Wollaston's principle, require this adjust-
136 MICROSCOPIC ILLUSTRATIONS.
tuent, in order that a fine definition may be obtained with
them. "The centre of the aperture must be in the
common axis of the lenses" of the microscope, " and the
image of the perforation formed by the condensing
lens must be brought by such adjustment into the
same plane as the object to be examined*."
Stops or diaphragms serve to increase the definition of
the outline of delicate objects. Thus, the cilia and inter-
nal structure of animalcules become much more visible
hy their aid than without it, especially when we have
single magnifiers only. They enable us, also, to reduce
the quantity of light, when using achromatic microscopes
with object-glasses of long foci; by which reduction our
observations on thin transverse sections of wood, as well
as on cylindrical and spherical bodies, may be more
accurately made.
With high magnifying powers it is often desirable to
have a lateral adjustment for the Wollaston illumination,
to effect which, a movement to and fro must be given to
the screw which holds the socket, on the under side of
the moveable stage (page 105) ; whilst the body admits
of a lateral adjustment, to the right or left in the other
direction. By these means we may obtain either a cen-
tral or eccentric pencil of light.
The reader must bear in mind, that stops have the
effect of decreasing the angle of aperture of the object-
glass; and therefore, in testing it, he must make proper
allowance for them.
* Philosophical Transactions, p. 'J, 1830.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 13J
Sect. 15. On viewing Transparent Objects by Day-light.
— The best position of the instrument by day-light is
that represented at fig. 29. When the object-glass is of
long focus, a screen must be interposed to stop the light
from falling upon the object. If this precaution be not
taken, we could not obtain a correct knowledge of it, on
.account of the confusion occasioned by the transmitted
and reflected light. They must not, therefore, be used
together. A small piece of black card placed upon its
edge, on the stage, will prevent the light from falling
upon a transparent body.
Sect. 16. On viewing Transparent Bodies by Intermitting
Light. — It has been ingeniously suggested, in order to
determine the number and arrangement of the rotatory
organs of Infusoria (such as the wheel-animalcule), to
illuminate them by a succession of galvanic or electric
sparks. By this means, an effect is produced similar to
that occasioned by the revolution of a cogged wheel when
viewed in a mirror. The reflection through the cogs
makes the wheel, although in rapid motion, appear
stationary.
As there are several methods by which this effect can
be produced, it is unnecessary to enter upon the details
here, some persons preferring one way and some another.
In my own experiments, I have used the sparks emitted
by the electric magnetism of a wheel dipping in mer-
cury.
138
MICROSCOPIC ILLUSTRATIONS.
Sect. 17. The Black Ground Illumination for Trans-
parent Objects. — The Rev. Mr. Reade, in the Appendix
to the Micrographia, has described a method of illumi-
nation for transparent objects, differing from any at
present in use. It consists in illuminating the object by
a very strong light placed at such an obliquity to the
axis of the microscope that none of the rays can enter it,
except those which impinge directly upon the object, and
are thereby bent so as to pass through the object into
the instrument. As the arrangement for viewing objects
in this way may not readily suggest itself from a verbal
description only, it has been thought advisable to illus-
Fig. 29.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 139
trate it more fully by means of the accompanying" en-
gravings, so that any one may make trial of it, and
thence form a correct judgment of its merits. I should
mention, that the effects produced are not so striking in
some objects as in others, and therefore that it is worth
while to make trial of several kinds.
Fig. 29 represents one of my instruments : its body,
eye-piece, and object-glass, n,i,e; the spring double-
stage, /; the mirror, o, which is turned aside ; the candle-
holder, k, I; and jointed condenser, m. In this arrange-
ment it is proposed to illuminate the object by an arti-
ficial condensed light. Let the object-slider be placed
between the stage and the circular plate; adjust to the
focus, and place the candle, /, and condenser, m, in the
positions shewn in the drawing, so that the pencil of rays,
r, r, may form the required angle with the axis of the
instrument, i, i. This angle will be dependent upon the
angle of aperture of the object-glass; but in all cases it
must exceed half that angle, in order to produce the
desired effect, otherwise the field of view will be illumi-
nated. But if a small transparent object, such as the
pollen of a flower, the scale of an insect, &c. be placed
within the field of view, the rays impinging upon it will
be refracted, so as to enter the microscope, and they
will form an illuminated image of it upon the dark
ground.
When this experiment is conducted by day-light, the
instrument should be placed in the position shewn by
140
MICROSCOPIC ILLUSTRATIONS.
fig. 30, with the condenser, m, to condense the light in
the manner there represented.
Fig. 30.
If the rays, r, r, make an angle with i, ?', similar to
that in the former case, the result will he the same. The
most convenient plan of managing this mode of illumi-
nating hy day-light, is hy means of a large concave
rellector fitted upon the stem of the candle-holder ; or
upon a separate stand, so placed that the reflected light
shall make the proper angle with the axis of the micro-
scope. The instrument, hy this means, may be placed
in a vertical position, if so preferred.
The medium power object-glasses, usually marked
B, are best suited for this method of investigation.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. \\\
Sect. 18. Method of viewing Opaque Bodies by oblique
refected Light condensed upon them by Mirrors. — It is often
necessary to examine an object under object-glasses,
which differ widely in their amplifying powers, or focal
lengths, when great difficulty is experienced in mounting
Fig. 31.
r^y<\
it, so as to accommodate it to them. For instance — ■
suppose the object to be mounted on a circular disc,
suitably for an object-glass of one-inch focus, it would
be barely possible to illuminate it with a silver cup,
adapted to an object-glass of l-4th of an inch. Deep
object-glasses necessarily require the silver cups to be
small, by which means it is impracticable to give an
oblique direction to the light. The method usually pur-
sued, is to employ a silver concave reflector of the form
shewn at /, fig. 31 ; by the aid of which light may be con-
densed upon the object, so as to exhibit it under object-
glasses of different focal lenghs.
In order to obtain a greater condensation of light, Mr.
142 MrcRoscopic illustrations.
Ross, who first proposed the adoption of this reflector,
places a condensing lens in front of the stage. The dis-
persion occasioned by this lens, however, is apt to give
a false colouring to the object ; so that I prefer
making use of a large concave mirror in the manner
represented in the above (fig. 31), which obviates this
defect, whilst it admits of the light being placed in a
more convenient position.
Sect. 19. A Method for determining the Forms of certain
minute Bodies. — In the investigation of long stick-shaped
bodies, it is sometimes difficult to ascertain Avhether a
section of these would be of a circular, or of a flattened
oval form ; since, in either case, the object, when at rest,
presents the same appearance to the eye of the observer.
It occurred to me, therefore, that by immersing a body
such as these in a fluid, which evaporates rapidly, the
currents occasioned by the evaporation would raise and
turn it upon its edges, so as to afford a view of its different
sides. This plan I found to answer my expectation fully.
As an example illustrative of this mode of verification
may not be without its use, I have thought it worth while
to present the reader with the following one : —
Take on the point of a penknife a specimen of fossil
infusoria (or more correctly speaking, the silicious cover-
ing of these creatures), place it on a slip of glass, or what
is perhaps more convenient, the tablet of an aquatic live-
box, the cover being removed. Having equipped your
microscope with a moderate power, and .adjusted it to
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 1-13
distinct vision, let a drop of spirits of wine, or ether,
fall upon the infusoria, and observe the effect. As the
evaporation proceeds, the shells of the creatures will be
lifted up, presenting1 to the eye alternately their edges
and sides, whilst they are kept in motion. When all
the spirit has evaporated, excepting so much as is con-
tained within the shells, they will lie on their sides, and
the fluid within them will flow towards the opening.
Thus a correct idea is obtained, not only of their external
but also of their internal forms.
The evaporation will be retarded by the addition of a
little water to the spirits of wine, and accelerated by the
use of ether.
Sect. 20. — On viewing the Currents in Fluids during their
Evaporation. — For conducting this experiment, the fol-
lowing method is to be pursued. Place the microscope
in a vertical position ; select shallow or medium-power
object-glasses, which with the body shall magnify from
about 40 to 100 diameters; or single lenses from a
quarter to the tenth of an inch focus. Take an aquatic
live box of moderate size, and place upon the centre of
it a drop of the oil of turpentine, or spirits of wine, &c.
Then cover it with the thin glass cover, taking care that
the thickness of the fluid be not more than about I -15th
of an inch.
If this fluid be quite pure, the motion of its particles
will not be perceptible : but Mr. Varley, who introduced
the experiment to the Society of Arts, grinds a small
1 i 1 MICROSCOPIC ILLUSTRATIONS.
portion of coal into it, which occasions the currents pro-
duced by the evaporation to be distinctly seen. The
specific gravity of coal not being great, these minute
portions are held in suspension during the whole expe-
riment. The following observations on this subject are
given in the Society's Transactions, vol. 50 : —
1 . A drop of spirit of wine, or of naphtha, exhibits two,
three, or four vortices, or centres of circulation, accord-
ing to the size of the drop ; and if the^e vortices are
viewed laterally, the lines of particles will be seen
forming oblique curves from top to bottom of the drop.
2. Oil of turpentine shews a rapid circulation in two
continuous spirals, one to the right, the other to the
left, around the drop. These meet in the opposite
diameter, from which the particles are slowly carried
across the diameter to the place of starting, and this
continues while there is fluid enough to let it be seen.
3. If, however, the drop does not exceed one-tenth of
an inch in diameter, it presents the appearance of par-
ticles continually rising up in the middle, and radiating
in gentle curves to the circumference.
4. If the liquid be put into a very small phial, similar
motions are perceived, the particles, when they have
reached the side of the phial, going down to rise up after-
wards in the centre or axis.
5. If a bubble of air be inclosed in the liquid, motions,
similar to those described in No. 2, are observed in the
part immediately in contact with the bubble.
DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 145
6. In a flat drop of new wine laid on the tablet or disc
of the aquatic live box, but not compressed by the cover,
the motion was a regular uniform circulation, the par-
ticles rising from below at one end of the drop, then
passing- straight across on the surface, and descending at
the other end.
1 40
CHAPTER VII.
Practical Remarks on Microscopes for viewing and drawing
Aquatic Larva, fyc.
By C. R. GORING, M. D.
The instrument which I used in executing the drawings
was a single microscope mounted with three achromatic
lenses of the 9-10tb, 6-10th, and 2-10th of an inch sidereal
focus. Had I not possessed these, I should probably
have used sapphires, or even equivalent common ones ;
for I greatly prefer a single microscope as a drawing tool,
from its being so very handy and manageable, and taking
up so little room on the table. All the necessary mo-
tions were given to the optical part, and not to the stage,
in order that living objects should be disturbed as little
as possible. I always found it make a great difference
for the better when they were allowed to remain un-
moved, for their natural restlessness, when exasperated
by motion, renders them completely intractable ; when
undisturbed, they will sometimes remain quiet for half a
minute together. An aquatic live-box*, of a little larger
See Plate, fig. 21.
DRAWING WITH THE MICROSCOPE. 147
diameter than the length of the insect to be drawn,
answers best to confine them : they may be kept quite
closed up, for they do not appear to me to require air to
support their existence. I was in the habit also of observing
them with a compound aplanatic microscope, having a
boot to slide over the objective end, so that it could be
introduced into the large transparent vessel filled with
water, which was their usual abode, and in which they
would remain pretty quiescent, especially when well
supplied with food. I must remark that Thames water
is utterly poisonous to nearly the whole race of aquatic
insects. I presume it is not necessary to say that every
species of camera lucida, and all the contrivances which
maybe used for tracing inanimate objects, are altogether
useless in drawing living ones. The colours of every
object are given as seen with the 9- 10th focus lens, having
its full aperture, as they appear in mere day-light, with-
out any artificial illumination whatever. I utterly dis-
approve of lamp-light for larvae ; it gives, indeed, a strong
outline, but confuses and more than half obliterates the
viscera, while it makes the colours very dingy and dull.
The tints of these objects become fainter and fainter, and
the shades darker and darker, as the magnifying power
is increased. I did not find it necessary to employ any
power beyond that of the simple 2-10th focus, in order
to develop the whole of their structure : superior powers
seem to me merely to magnify, without shewing any
thing about them (except the circulation) more satisfac-
torily, and do not take in a sufficient portion of the object
148 MICROSCOPIC ILLUSTRATIONS.
for a pleasing view. When we want to examine these
objects merely for the purpose of amusement, it will be
advisable to use compound instruments, on account of
their large field of view, luxurious accommodations, and
arrangements : their powers must be made equivalent to
the single lenses I employed, namely, one inch, half an
inch, and a quarter of an inch focus, which require their
objectives to be about four, two, and one inch focus re-
spectively, (as the weakest compound body which can
be applied usually quadruples the power of the object-
glass.) For the reasons stated above, all the requisite
motions and adjustments must here also be given to the
optical part, and not to the stage. It will also be found
a very great convenience if the stage is so constructed as
to admit of being altogether removed, so that any large
body, such as a square vase on a large flat slider, con-
taining the objects, can be substituted in its place, in
order that there shall be no necessity to remove the
insects from their usual places of abode in the said
vessels, &c. as they are very apt to receive injury and
become restless by such removal. In order to effect this
very desirable arrangement successfully, it will be neces-
sary that the bar of the microscope, instead of working
upon the stand with a cradle joint, should possess a ca-
pability of turning round by moving in a ball and socket,
or some other similar contrivance, so that the space
occupied by the stage may fold down on one side, and
allow of the introduction of the jar, &c. into it on its ap-
propriate stand; when, all the necessary adjustments
DRAWING WITH THE MICROSCOPE. 149
being possessed by the optical part, the instrument is
just as perfect and manageable without its stage as with it,
and may be used upon any large body whatever, which will
be found a great convenience. This construction also
gives great facilities for demonstrating all sorts of test
objects, as well as for verifying and proving the nature of
bodies inspected — (a subject which is as yet understood
by few observers.)
With respect to the exhibition of larvae, &c. in the
solar microscope, it may be observed generally, that what-
ever object-glass shews them well in a compound aplanatic,
with the assistance of the body and eye-glasses, will shew
them unassisted in the solar instrument, because the dis-
tance to which the rays are suffered to diverge does the
work of the compound body in giving the necessary
amplification, which it is the peculiar property of this
instrument to effect to a vast extent, without altering the
size of the field of view. A solar microscope may in fact
be defined in its optical principle as a mere object-glass,
forming an image on a skreen, instead of the space in-
cluded in the field bar of a compound body.
C. R. G.
150
CHAPTER VIII.
Whether there is a best possible ivay of constructing the
stand, or mounting, fyc. of Microscopes {the specific pur-
pose or purposes to which they are to be applied being first
determined) ?
By C. R. GORING, M. D.
i
I apprkhknd that the construction of all kinds of me-
chanical implements, tools, utensils, musical, philo-
sophical and mathematical instruments, &c. may be
reduced to fixed principles, and that one best possible
way of making them, may, and can be discovered, (when
the specific and particular end and object of their fabri-
cation is duly settled). It is otherwise with all those
manufactures which are of an ornamental nature, and
therefore subject to the caprice of taste and opinion ; and
also with every thing made for the gratification of any
of our senses, or for the ease and accommodation of our
personal wants. Thus it would be very absurd to pre-
tend that there is a best possible system of cooking, or
making caps and bonnets, unless wTe choose to assume
the position, that the specific end of cooking and mantua-
making being the gratification of the whims and fancies
of some particular individual, even these arts are reducible
ON CONSTRUCTING STANDS OF MICROSCOPES. 151
to fixed principles (such as they are). Every hing
connected with the fine arts always resolves itself into
a matter of opinion, about which it is perfectly useless to
contend, because every man considers his own private
judgment, however outre or singular, as of equal value
at least with that of his neighbour's. The standard of
taste is, then, a mere chimera, because it differs like
the face, or form of the limbs, in every particular spe-
cimen of the human race ; unless, indeed, it might be
ascertained by taking the average of that of the whole
species.
However, mankind seem to have come to a common
decision concerning the utility, excellence, and supe-
riority of many things, and to consider them as incapable,
or nearly so, of any real improvement. This is the case
with regard to many points, even determined by the
judgment of the senses; but more so with regard to
hose whose value is supposed to be ascertained by the
test of experience. Thus a variety of mechanical tools,
&c. may be considered as erected into standards, and not
at all likely to undergo modification in future. Even
musical instruments, as regards the quality of their tone
and sound, seem to have arrived at a regular and deter-
mined mode of construction.
Now, if so many other things have been perfected and
erected into standards, by the common consent of the
human race, why should not microscopes also? Why
should we not bend the whole force and power of our
invention and reflection towards the fabrication of every
152 MICROSCOPIC ILLUSTRATIONS.
thing1 connected with them, till every point is effected in
the hest possible manner ? These instruments have under-
gone a complete revolution in their optical parts, and
become truly dignified and respectable : assuredly their
mechanical structure should correspond with the advance
which has taken place in their optical constitution.
However, like other things, they are varied in their
construction to serve particular purposes. Thus, if made
merely for commerce, or to look at, or to wear in the
waistcoat pocket, like a snuff-box, they must evidently
be made on a plan quite different from that required for
scientific observations.
I pretend not to meddle with matters concerning com-
merce; the trade understand them far better than I do,
and shall therefore merely observe, that several indivi-
duals experienced in business have assured me, that the
first thing to be considered in the construction of a mi-
croscope is its price ; and the second, the size of its case,
and how it is to look when packed in it, with all its little
eye-traps and trinkets about it. It is frequently sold in
two minutes, long before the merits of its construction
can be known; therefore one kind is just as good as
another, the public at large being no judges or con-
noisseurs in such matters.
Again, instruments may be made expressly for trans-
parent objects, or opaque ones, or even some particular
class of those bodies, for lamp-light only, or for that of
the atmosphere, for drawing, for public exhibition, &c.
all of which circumstances will produce a variation in
ON CONSTRUCTING STANDS OF MICROSCOPES. 153
their fabric, while they are correctly adapted to their in-
tended use, and, therefore, perfect in their kind. The
construction which I wish to discover myself, is that of
an approximation to a standard for general purposes ; and
I think the principles at least of such a structure may be
ascertained, though the best possible way of carrying them
into effect, perhaps, cannot at present — at least by myself.
In the first chapter* I have already sketched an outline
of the kind of instrument which I here propose now to
fill up and reduce to a determinate form, but shall first
detail a few of the obstacles which all who attempt to
reform the construction of microscopes may be expected
to encounter. First, there is the inveterate hatred and
contempt of all innovation whatever, which seems to
form a part of our nature, when arrived at a certain
period of life. Men long used to some particular way of
doing any thing, cannot endure the idea of going to
school again, and learning to act upon a new system.
The very idea of the possibility of being taught any thing,
galls and wounds their self-love to the quick : if this
concerns a matter relative to their particular profession,
or something, perhaps, on which they peculiarly pique
themselves : they become altogether indignant and
furious. If by any possibility they arc brought to recog-
nise the necessity of some change, they must make it
themselves j what a disgraceful and lamentable poverty
* Chapter VII. in this edition.
154 MICROSCOPIC ILLUSTRATIONS.
of genius would it not shew, to copy a good thing which
had heen invented by another man !
It cannot be denied, moreover, that there really is a great
deal of trouble in getting up new philosophical instru-
ments of all sorts. There are fresh patterns to be made,
and tried, and re-made ; workmen to instruct afresh, and
after all, particular parts of the instrument may not fulfil
the intended purpose, and must be remodelled ; all of
which circumstances occasion a great deal of annoyance
and expense, and naturally render men averse from the
adoption of new constructions ; more especially as the
public at large never can be imbued with a sense of the
difficulties, expense, and loss of time, occasioned by
what are called out of the ivay jobs, and consequently
can never be induced to pay for them so as to remunerate
the artists employed.
If it is indeed true, that conceit is given to man to
console him for want of talent, and that the less of one
of these qualities he may possess, the more he is likely
to have of the other, what must be the consequence,
should it happen that an individual, possessing seventy-
five parts of conceit and twenty-five of talent in the
hundred, comes in contact with something invented, or
recommended, by a man who has but twenty- five of the
former quality to seventy-five of the latter ? Is it likely
he will adopt it ? Never. He will imagine that he can
produce something infinitely better, and will be still
more strenuous in this opinion if he happens not to
ON CONSTRUCTING STANDS OK MICROSCOPES. 155
possess a grain of experience on the subject under deli-
beration.
All these considerations have had so much weight
with me, that I have more than once determined never
to meddle with the stands and apparatus of microscopes
at all, but leave men to settle them according to their
own fancies ; but my friends have told me, that I have
as good a right to consider an ounce of my own wit equal
to a ton of my neighbour's as other men have, and
that I ought to make the experiment, of giving a con-
struction of my own, whether it may be adopted or not.
I shall therefore state my own views on the subject, and
for every particular structure recommended, shall give
a reason which every man may, of course, either admit
or disprove, together with the construction deduced
from it. First, then, I say that the stage should be mo-
tionless, and that the optical part only should possess the
requisite power of traversing and adjustment ; because
living objects are much more quiet when allowed to
remain at rest, and therefore more easily observed : if
some one who has been less plagued by them than I
have, chooses to say that it makes no difference whether
they are moved about or not, I will give up the point ;
but still insist on the propriety of making the instrument
perform all its adjustments as perfecthj without the stage as
with it, for then we may remove the stage altogether if
we please, and substitute any thing we think proper in
its place, and all will go on as before. This arrange-
156 MICROSCOPIC ILLUSTRATIONS.
raent gives us the power of examining small parts of
large bodies without detaching them from their wholes.
Thus we can examine the contents of a vase of polypi,
or acpiatic insects, or a small part of a large specimen of
a mineral, or a nosegay of flowers, with the insects
which inhabit them ; or with an erecting eye-piece we
may apply the instrument to a turning-lathe or some
piece of delicate machinery, and work upon it much
more comfortably than by the help of single lenses. But
for these purposes the space occupied by the stage must be
left free and open; and to obtain this accommodation the
bar of the microscope must swing round on its stand in
any direction, on a ball and socket joint, which con-
joined with a rotatory motion of the arm on the top of
the said bar, will almost always enable us to gain the po-
sition required. An instrument which does not possess
all these properties will only do half the work it ought to
perform. It must be evident, also, that this construc-
tion gives the utmost facility for introducing a lamp or
candle, either close behind the stage for transparent
bodies, or before it for opaque ones ; and this arrange-
ment is a point of the last moment for demonstrating
and verifying a variety of objects, particularly proof
opaque ones, as I shall shew in due season, when I come
to treat on them and on the subject of verification. No
microscope which is from any cause lame or impotent,
either in its optical or mechanical construction, can be
fit for such purposes.
ON CONSTRUCTING STANDS OF MICROSCOPES. 157
The stage must also possess a capability of turning
round on a pivot, so that by tilting the microscope we
may be enabled to view the side or elevation of a body
as well as its plan ; for example, the curve of a small
lens, when laid flat on its face, the edge of a razor, the
point of a needle, &c. without using any particular ap-
paratus to preserve such bodies in the position in which
we wish to see them. The use of such a mode of ob-
serving, in cases of dissection, must be manifest; for in
this way the side of an insect, &c. may be viewed and
worked upon without disturbing the parts laid open, in
the horizontal position, and thereby occasioning much
extra trouble and confusion. By turning the subject
round on the stage, every elevation or side view of it may,
of course, be successively obtained.
There is yet another advantage to be gained by a rota-
tory motion in the stage; for if we employ a diagonal
objective, and tilt both the stage and the bar into a hori-
zontal position, so that the body of the microscope shall
be under the stage, we can examine crystallizations of
salts without being annoyed by the steam which arises
from them during consolidation, and which is almost
certain to condense on the object glass when used in any
other position. In the present case this is impossible;
for nothing but the under surface of the glass on which
the salt is placed, is presented towards the object glass.
All sorts of fluids, and the bodies contained in them, may
in the same way be managed without being troublesome,
158 MICROSCOPIC ILLUSTRATIONS.
and thus chemical actions of all sorts may be studied under
a magnifying power.
Moreover, the stage must be enabled to shift down to
the end of its bar, so that wTe may use object-glasses of
long foci, and also place any large bulky body upon it
without building up the whole instrument to an extrava-
gant height, and thereby rendering it top-heavy and
rickety. It must also be of such strength as not to spring
under the weight of our hands when used for dissection ;
for if it does, it will be utterly impossible to preserve a
steady focus, which will be found a dreadful nuisance
with a high power, and indeed with any power. Its size
must also be such as to afford a sufficient support for the
hands. The distance of the hole in which the slider
holder is fixed from the bar, must also be such as to allow
a slider to turn completely round, otherwise we cannot
get test objects into that position relative to the light in
which only they can be demonstrated. (This is especially
the case with the markings on the scales of beetles and
butterflies.)
I do not much approve of attaching illuminators to the
stage, either for opaque or diaphanous objects. It will
be found much more commodious to cause the spectrum
for opaque objects to travel along with the body. Accord-
ingly, a condenser should be attached to it. Both the
mirror and condensing lens under the stage should be
caused to swing round by means of a spring socket and
pinching screw working on a round bar, so that they
ON CONSTRUCTING STANDS OF MICROSCOPES. 159
may be instantly removed out of the way when not
wanted, without being detached from the bar.
The large illuminating mirror should (if not of very
considerable dimensions) be made oval, and should work
upon a swivel joint at the bottom instead of the side,
otherwise it will be rendered unserviceable, for the long
axis of the ellipse cannot otherwise be brought into the
position necessary to give a round spectrum when placed
at the requisite angle for illumination, say 45 degrees.
The reason for the ellipticity of the mirror is this : — An
image of it is constantly formed in the optic or visual
pencil, at the eye-piece, as maybe seen with a magnifier
whenever bodies are viewed by the intercepted or trans-
mitted light which it furnishes. Now unless this image
is of equal size with the said visual pencil, an effect is
produced not very dissimilar to that of mutilating the
pencil in some other way, and exactly the same as to the
quantity of light lost. Now a round mirror (unless it is
of such size as to allow for the cutting off occasioned by
its angular position,) gives an elliptic pencil. But I
presume it is always advisable not to increase the bulk
of any part of an optical instrument when it can be
avoided; consequently the true form for the mirror is an
ellipse. This form does not easily admit of the use of a
concave reflector; but I disapprove of them, as they
always seem to me to occasion a certain indistinctness in
vision by intercepted light, and if wanted only for illu-
minating opaque objects, by the help of silver cups, may
be dispensed with ; for a much better action is produced
1G0 MICROSCOPIC ILLUSTRATIONS.
by a plane mirror, co-operating with a condensing lens.
Because an angular plane mirror and a condensing glass
produce a round spectrum; whereas a concave mirror,
when tilted, always gives an oblong one ; however, in
the present construction, I always suppose that when
silver cups are employed, the condenser is to act by itself
without any mirror at all, by which arrangement the
maximum of illumination is given.
The size of the mirror is determined by its distance
from the object-glass, or single magnifier used, and by
the angle of aperture possessed by them. The longer
the bar, and the greater the aperture of the optical part,
the larger must be its dimensions to fill up the visual
pencil.
The reverse of the mirror will be best occupied by a
surface of plaster of Paris, to reflect the light of the sun,
which will be found of great use in ascertaining the true
tints of transparent objects, the colours of which are
shewn by this sort of light with the utmost truth and
delicacy, far better than when brought out by a piece of
ground glass interposed between them and the polished
mirror. The double action of the mirror will be com-
pletely commanded by the most inexperienced observer,
if a milled head is attached to its transverse axis, as will
be shewn in its proper place.
Now these are, I think, the main and capital points to
be attended to in the construction of a stand. As, how-
ever, every question is said to have two handles to it, I
shall endeavour to discuss the merits of some opposite
ON CONSTRUCTING STANDS OF MICROSCOPES. 161
constructions. First, then, it has been said, that the
double motion of a ball and socket joint is of a most un-
manageable nature, and that a cradle joint is a true,
regular, and far superior movement : this I admit, and
should say, that if a telescope had, by means of a ball
and socket, to follow the motion of a star, no motion
could be more unappropriate and detestable ; but in a
microscope it happens always to be a fixture, and when
clamped tight by means of a pinching-screw, is as steady
as a rock.
This observation may appear very unnecessary to my
readers in general ; but I have met with individuals of
such obtuse understandings, that they cannot be brought
to comprehend that a telescope performs a part of its
motion by means of its cradle joint, whereas that of a
microscope is the result of a traversing motion in its arm,
combined with a rotatory one on the top of the bar, and
therefore has nothing to do with that on the head of the
stand, be it what it may, which is always a pro tempore
fixture.
Again, it has been said, that by giving the motions and
adjustments to the optical part, it is rendered much less
steady than it might be under other circumstances ; that
it is like mounting a telescope on a mop-stick ; that
immobility is of most virtual importance for observa-
tion, &c. I answer, that by making the work sufficiently
strong and solid, and the optical part no larger or longer
than is necessary, the instrument is rendered abundantly
steady, and free from tremor even with its highest powers.
M
1(32 MICROSCOPIC ILLUSTRATIONS.
At the same time I willingly admit, that if the body is
made very long or large it will be almost impossible to
combine the stability requisite for practical purposes
with a capability of traversing and adjustment.
It has been asserted, that if after we have adjusted our
light for viewing a transparent object satisfactorily, we
throw the axis of the optical part out of the position
which we first selected, we must begin our work of illu-
mination over again, or lose the effect of the original
one. This is true beyond certain limits, but the body of a
microscope may be moved very considerably, without in
the least affecting the vision of ordinary transparent
objects, and to opaque bodies, of course, the observation
cannot apply. Further, it is said that the employment
of cones and diaphragms below the stage is of vast use
in developing the nature of many transparent bodies,
and in tempering the light to the shade to produce a
maximum of distinctness ; and that if these are employed,
the most perverse and prejudiced antagonist cannot re-
fuse to admit that any diversion of the optical part from
the line of adjustment must utterly destroy, not only
distinctness, but nearly all vision whatever.
To obviate these objections let there be a large roomy
slider-holder, with a good steel spring, so as to pinch the
plates together pretty tight ; the object can then be moved
about by the hands in any direction, and the body may re-
main a fixture, save as to the adjustment of the focus.
I have always found that people like to move an object
about with their hands, even when they have screw mo-
OX CONSTRUCTING STANDS OK MICROSCOPES. 103
tions for traversing, and indeed I prefer it myself, (pro-
vided the object does not yield too easily,) even with very
high powers.
Lastly, it has been remarked, with great justice, that
if we choose to employ any of the generation of camera
lucidas for drawing objects, they can only be used with
microscopes in which the body is altogether immoveable.
Nothing is more certain. At the same time I cannot re-
frain from expressing my hatred and contempt of the
Whole! tribe, as rather impediments than helps to a real
draughtsman. This much I will venture to say, that if
a man cannot draw ivithout them, he cannot ivith them.
The slider-holder enables the present construction to
operate with these nuisances, for the adjustment of the
focus will not sensibly disturb that of the image on the
paper, and if it should, a very little motion, backwards
or forwards, given to the drawing, will re-arrange it.
The only aid which I can with confidence recommend*,
as of real utility, is a micrometer, composed of glass,
placed in the field bar of the microscope, and divided
into about 40 or 50 parts to the inch, with double divi-
sions, or very strong lines at every fifth space. These
should be rubbed over with black lead, after which they
must be burnished with the edge of a piece of hard
wood, so as to clean the surface of the glass ivithout rubbing
the black lead out of the divisions, (a device of the late
Dr. Wollaston, and bearing the stamp of his original and
* See Micrograpbia, p. 221.
164 MICROSCOPIC ILLUSTRATIONS.
penetrating genius) ; then let another piece of thin plane
glass be smeared with Canada balsam, and cemented
upon the divisions, which will preserve them for ever.
Now if corresponding black lines, of any scale required,
are placed under the paper on which we draw, we can
with great facility put in our outline in the most correct
proportions. Or if the paper is too opaque, a frame
with black silk threads stretched upon it may be laid
upon it till the sketch is completed. The contrivance
can be used with my microscope as well as with any
other.
Mr. Lister has constructed the stand of a microscope
with a particular view to the use of the camera lucida :
accordingly his body is motionless and of considerable
length, so as to clear a large space on the table for the
field of view. The ocular end is, moreover, firmly lashed
to the legs of the stand, (which is very solid,) by means
of steadying rods, forming altogether the best construc-
tion for the use of long heavy bodies, and cameras lu-
cidae, which I have seen.
It must be most evident that a single microscope re-
quires exactly the same powers, properties, and capa-
bilities as a compound one. I should, therefore, construct
its stand and apparatus precisely in the same manner as
that of a compound one, only it may be made on a much
smaller scale : as little strength is required for carrying
single magnifiers, triangular drawn tubes may be used
instead of the triangular gun-metal bar of the compound
(to be hereafter described). The drawing of triangular
ON CONSTRUCTING STANDS OF MICROSCOP&S. ] 65
tubes is a novelty produced by Mr. Pritchard expressly
for his diamond and sapphire instruments.
I therefore conclude that the principles, at least, of the
best possible construction for the mechanical part of
microscopes, may be denned. I have attempted to re-
duce them to practice in an instrument the patterns of
which 1 have executed with my own hands, and Mr.
Pritchard has made a mechanical drawing of it, which
he will describe in the next chapter, under the title of
my Operative Aplanatic Engiscope. Before, however, the
description proceeds, I must beg a boon of my readers
and the microscopic world at large, viz. to permit me
to supplant the term Compound Microscope by the word
Engiscope, which seems to me more apposite.
It is derived from two Greek words, iyyvg, near, and
oKoniu, to view, and therefore well expresses an instru-
ment for viewing close objects, or for viewing objects
closely, and is in strong contradistinction to the term
telescope, derived, as my readers well know, from Ttkot;,
an end or distant limit, and cko-item, and therefore denoting
an instrument for viewing distant objects. The term
microscope, derived from fmywc, small, and (tko-kIw, sig-
nifies an instrument for examining small objects, which
is perfectly correct also, but in bad contradistinction to
the telescope, which would have to be named megala-
scope, to oppose it (from /^'yctc, great, and okowIu),) which
expression would be perfectly accurate when applied to
the telescope, for it views very large objeets, such as the
totality of a planet or the sun, &c. Now a compound
16G MICROSCOPIC ILLUSTRATIONS.
microscope and a telescope pass into each other by in-
sensible degrees : a species of telescope can always be
made of the former, and a kind of microscope of the
latter, but both of the most execrable kind. To this last,
namely, a short spy-glass, or perspective glass, with a
long pull-out tube, so as to permit it to adapt itself to
rays which are considerably divergent, the term Engi-
scope has already been applied by Martin and others, but
I think most unwarrantably, for such an execrable piece
of trumpery is wholly unworthy of a separate existence,
or a separate name ; it is just as easy to make a piece of
velvet of an ass's hide as to make an object-glass which
shall answer both for a telescope and a compound mi-
croscope, be its focus what it may. The only veritable
engiscope is the latter instrument, with an objective-glass
truly adapted to act with divergent rays ; a short tele-
scope may be made of six inches focus, and a long com-
pound microscope with an object-glass also of six inches
focus, but the construction of each must be utterly
different, or they will only nominally be what they are
called.
I therefore hope that I shall be allowed (as I have
reformed and revolutionized both the optical and mechanical
structure of microscopes) to change their names also, and
shall therefore take the liberty of using the term engi-
scope, as aforesaid, instead of compound microscope,
and retaining the expressions microscope or simple mi-
croscope, for convenience sake, to denominate what is now
called i\ single microscope, in opposition to a compound,
ON CONSTRUCTING STANDS OF MICROSCOPES. 16/
The term compound microscope will then be applied
appositely to all those instruments with which we view
real objects instead of images of them, constructed by com-
bining two or more lenses together; for the optical part of
what is commonly called a single microscope may be made of
as many as four glasses, whereas the optical part of a com-
pound (as it is usually termed) does not necessarily consist
of more than two, viz. an object and ocular glass. Thus
if we retain the old terms, how are we to define accu-
rately a magnifier composed of two double aplanatics ?
Are we to christen it a single quadruple, or double
doublet ? or a simple compound ? This will be as ludi-
crous as Mr. Callaghan O'Brallaghan's definition of the
first bit of bread he ate in England, which it seems was
a roasted potato, cooked in a brass saucepan.
It is presumed, therefore, with due deference to the
opinions of better men, that the term engiscope is lawful
and orthodox, and will, probably, be adopted by posterity,
if not by the present generation : as to the fuss which
has been made about my using an i instead of a y, in the
conversion of the Greek upsilon (both letters having
the same sound, and having been used indifferently by
ancient English writers), I beg to state that I did so on
purpose, to make a tub to amuse the ivhale icith, and to
draw the attention of the learned to the term.
C. R. G.
168
CHAPTER IX.
Description of Dr. Goring' s Operative Aplanatic*
Engiscope.
It is necessary to premise that figures J, 8, 10, 11, 12,
14, 17, 18, 19, 20, and letter A, are drawn one-quarter of
the real size ; all the rest are one-sixth, exeej>t figure 23,
which is of the true size.
Figure 7 represents a geometrical elevation of the in-
strument, just removed from its case, the body, «, being
screwed on, and the triangular bar, b, somewhat ele-
vated above the stage, which is fixed in situ. To begin
from the foundation, — the legs are all of the same thick-
ness, but tapered in breadth towards their extremities,
in order to obtain strength where most required. In
the upper one is a hole to receive the projecting pin at
the end of the circular bar, c. Underneath the pillar, d,
is a screw nut, e, which lets down, to obviate the spring-
ing of the legs. The pillar, d, is constructed of two
pieces of very stout tube, moving stiffly in each other.
At the head of this pillar is a socket,/^ to receive the ball
shewn in figure 8. This universal joint is made in the
* Jplanatic, derived from the priv. a, and irAavT), error, means free from
both kinds of aberration, or devoid of all errors.
DESCRIPTION OF DR. GORING's ENGISCOPK. 1G9
customary manner, but the socket lias a slit for the neck
of the ball, only through one-quarter of a circle, to avoid
weakening it unnecessarily. It is pinched by a screw, g,
with a vice-handle. The ball, the socket of the circular
bar, h, together with the stage- pin, i, are all cast in one
piece, as shewn in plan, fig. 8. The stage, j, has a cir-
cular aperture, which has a sink and two nicks in it,
together with a square hole, k, (as seen in fig. 9). There
is likewise an arrow pointing to a nick in the socket,
h, to shew when it is truly at right angles to the bar, b.
It fixes on to the pin, i, which is clamped tight by a
screw,/.- into the bottom of this screw is inserted a
piece of metal, the end of which is worked to correspond
to the curve of the pin, i, which causes it to clamp tight
with a very slight effort, and preserves the pin from in-
jury. Within the socket, h, is soldered a stout tube,
forming the external bar, c. On this circular bar slide
the split sockets, m, m, m, carrying the condensing lens, n,
the inferior pin, i, for holding the stage, and the oval
mirror, o : all travel up and down at pleasure, and may
either be moved out of the way, by turning them one-
quarter round, or stripped off altogether, if thought more
convenient. Their clamping screws fix them tight in
any required position. A nick is made in front of each
of the sockets, and a line drawn on the front of the bar,
to shew when the condenser and mirror, &c. are truly in
the axis of the aperture of the stage. The oval mirror is
plaoe, but its reverse is formed of plaster of Paris. It re-
volves on a vertical axis, />, and on a horizontal one, q,
1/0 MICROSCOPIC ILLUSTRATIONS.
the motions of both of which are governed by the milled
head, r. The triangular gun-metal bar, b, is truncated at
its edges, and is therefore strictly speaking a hexagon,
tl us form giving greater strength in proportion to the space
occupied by it than a perfect triangle would, while it still
possesses the property of being locked fast when pinched
on only one side : it is evident that even an equilateral
hexagon would, when pinched on one side, always cause
two others to bear close against a triangular containing
tube. This bar slides up and down in the external cir-
cular one, c, between two plates of metal, pierced with
triangular apertures to receive it: one is soldered in at
the summit of the socket, h, the other below the milled
head, s ; and springs are placed on the same side as the
rack, both above and below the pinion, to steady the
bar, and give the friction necessary to prevent it from
falling from its position by gravitation. If the present
stand was made to operate solely with an engiscopic refract-
ing body, it would be better to omit the rack-work of the
upright bar altogether, and substitute a pinching screw
for it, giving a fine movement to the body within the neck
of the arm, by a screw on Ramsden's principle. In
its anterior side is sunk the rack which adjusts the focus
by means of the milled head, s, which is repeated on the
opposite side. Rack-work is not perhaps the best sort
of movement which might be contrived, but it is good
enough, when well executed, for all practical purposes.
On the top of this triangular bar is fixed the gun-metal
wheel,/, within the teeth of which works an endless
DESCRIPTION OF DR. GORING's ENGISCOl'K. l/l
screw, the milled head of which, u, is seen in the draw-
ing. Above the wheel is shewn the triangular pinion
socket, v, which carries the arm, w, which is also of gun-
metal, truncated at its edges with a sunk rack on its
superior side, exactly on the principle of the other : this
bar is worked by a pinion, x, seen in the cross elevation
of this socket and bar, fig. 10. Diamond and sapphire
lenses, and all sorts of simple microscopes, are attached
to this arm, by being thrust into the hole at its other
extremity, as drawn in the engraving.
The superiority of sapphire lenses over those of glass
seems now universally recognised, and virtually, the su-
periority of diamonds over sapphires. (For whatever will
prove the former of these propositions will most assuredly
prove the latter also.) If these substances possessed no
other advantages over glass, save their invulnerability
and capability of being burnished into their brass settings,
these properties, coupled with their extreme thinness, the
natural result of their shallow curves, when properly
executed, (and which allows more room for the object
and for the illumination of it, if opaque, with any given
power and aperture,) and their superior magnifying
power with a given curve, also would fully justify the
patronage they have received*.
The pinion, x, fig. 10, has a projecting square at each
end, to receive the ivory milled lever, ?/, or milled head,
z, on either side. The whole of this socket revolves on
* See Microscopic Cabinet, chap. xiv.
172 MICROSCOPIC ILLUSTRATIONS.
the upright triangular bar, b, and is kept in its place by
the gun-metal garter-piece, shewn at 'a, and has a saddle-
piece well screwed on, covering it over, to prevent the
loosening the pinion, by the action of the milled lever.
The endless screw may be detached from the wheel, t,
hy slackening the pinching screw, b, which serves to keep
the pinion in gear, the said endless screw being affixed
to a separate piece, which turns round on the project-
ing and inferior part of the socket, by means of a pivot :
the pinching screw, 'b, operating in an arc, formed to
receive it. This wheel and endless screw are absolutely
necessary to enable us to command the motions of the
arm, when the axis of the body of the instrument is not
perpendicular, or nearly so.
The body, a, is constructed on the smallest scale on
which it can well be made without impairing its optical
properties. The only true way of preventing the genera-
tion of false light is to allow so much space in the body that
the rays proceeding from the object-glass shall not impinge
on any part of the tube ; for no sensible light is produced
until they flash against something. Into the superior part
of the eye-tube, 'c, are screwed the various inverting eye-
glasses, and into its inferior part, 'd, the erecting glasses,
A. Upon the neck of the object end, 'e, are screwed the
various object-glasses, oneof which is represented attached
in the plate. Upon this neck also slides the illuminator, '/,
for opaque objects ; it has a split socket and clamping
screw, '(/, by which it is adjusted, and is composed of a
plain convex lens, having an inch and a half of aperture
DESCRIPTION OF DR. CORING's ENGISCOPK. 173
and the same focus operating- by lamp-light, with another
isosceles convex of same power and diameter screwed to it :
these curves have been found by experiment the best both
for refracting the maximum of light, and for preventing
any loss of it by reflection from the convex surfaces of
the lenses, 'h is the cap of one of the eye -pieces in dotted
lines ; it is supposed to be removed for the purpose of
applying the camera lutida, fig. 1 1, which is thrust on over
the eye-tube, a side view whereof is represented at fig. 12.
By far the best species of camera lucida is, I think, this
(which is the invention of Professor Amici), and is com-
posed of a simple piece of thick plate glass, with truly
parallel surfaces, placed at an angle of 45°, and reflecting
an image while we see through it, for it allows the point of
the pencil, the drawing on the paper, and the image, to be
seen at the same identical moment, without any dodging
or effort. Care must be taken to have a sufficient thick-
ness of glass, to prevent the visual pencil from reach-
ing the inferior surface, otherwise there will be two
images.
Fig. 13 is a micrometer, to be placed in the field-bar
of one of the lowest eye-pieces. It is made of glass, with
divisions of 40 or 50 parts to the inch, which are filled
with black lead, well burnished in, and secured by
another piece of glass being cemented over them.
Figure 14 is a square bar, sliding up and down in the
square tube in the stage, k, fig. 9. It carries the illumi-
nator,/, when it is thought advisable not to load the body
with it.
17^ MICROSCOPIC ILLUSTRATIONS.
Fig. 15 represents the lengthening tube, 'i, with the
direct boot, 7c, drawn over it. The lengthening piece
screws on in place of the object-glass, which is again
attached to its extremity. This piece, from its narrow-
ness, will generate false light; it must, therefore, be lined
with black velvet, which is, perhaps, the best substance
to stifle it when generated.
Figure 16 is the diagonal boot. It is constructed in the
same manner as the other, but has a plane metallic specu-
lum or rectangular prism of glass placed at'/, to reflect
the rays received at right angles. It is necessary that
the piece of plate-glass which is affixed to the extremity
of the cones of these boots should be very perfect, and
set in truly parallel.
SirD. Brewster first conceived the project of causing an
aplanatic objective to be so constructed that it should be
capable of acting in wrater instead of air (see his Treatise
on New Philosophical Instruments) . I am afraid it would
be very difficult to make a naked object-glass water-tight,
and at the same time to adjust it perfectly ; and after all it
would only serve to act in water, and would be useless out
of it. The present arrangement really seems to answer
every practical purpose completely well, though cer-
tainly Sir David's plan is the more scientific way of doing
the thing.
Figure 17 is a cup or silver speculum, which slides
over the end of the object-glass.
Figure 18 is a shade to slide over the lengthening
piece, 'i, figures 15 and 16.
DESCRIPTION OF DR. GORINGS ENGJSCOPE. 1/5
Figure 19 is a small cone, to slide over the object-
glass when acting by plain artificial light.
Figure 20 is the arm by which the optical part of the
AmicianCatadioptric Engiscope* is attached to thepresent
stand : it must be considerably longer than the other,
and, like it, racked to its extremity, to admit of its being
taken out of the socket. By means of its swivel and
pinching-screw, it allows the body to turn round,
and present itself either in front or at the sides of the
stage.
Figure 21 is the aquatic live-box, with an extra pierced
lid, 'm, for aerial insects and land objects, &c. There
should be about half a dozen of these, of different sizes,
varying from that given in the plate, to about 2-10ths of
an inch in diameter. It would be found a convenience
if the larger ones had watch-glasses fixed into them with
their curves applying to each other, and their concavi-
ties pointing outwards, instead of the plane glasses, as
given in the drawing ; for by this arrangement, when
used with very low powers for exhibiting a grand melee of
aquatic insects, &c, taking in nearly their whole area,
the edges of the field will be as distinct as its centre;
the foci of these two parts of the visible superficies being
always different with aflat object, and a low power, even
with the best aplanatics.
The glasses, whether flat or concave, must be well
cemented into their cells by painters' ground white lead
or opticians' cement, that the box may be completely
* Micrographia, chap. i.
1"6 MICROSCOPIC ILLUSTRATION'S.
water-tight ; and the tubes themselves may be greased
for the same purpose if necessary. These boxes are as useful
pieces of microscopic apparatus as ever were invented.
Figure 22 represents the black ground box (an inven-
tion of Mr. Lister), which in the present instrument also
forms a stage for the single microscope, and for dis-
section.
At 'n is seen its lid, of which a side view is given at 'o ;
at 'p, its bottom with its side view also j its interior
surface is lined with black silk velvet, and so is the
superior surface of ihe lid ; the sides of the cone, 'q, are
well blacked ; at 'r is seen a disk, also covered with black
silk velvet, which acts along with the silver specula.
Its arm revolves on the top of the cone, and can be
removed altogether, if necessary ; at its extremity is a
hole, in which is inserted the cradle joint, which carries
a brass needle; a small piece of brass tube, stuffed with
cork, is affixed to one of its extremities, and to the other
a pair of forceps, which are represented of their full size
at figure 23. These are constructed as usual, except
that a hole is drilled through them at 's, to enable them
forcibly to grasp the head of a common pin.
Figure 24 is the piece which carries the wheel of dia-
phragms ; 't is the plan of their under side. There should
be about five apertures, varying from half an inch to
1- 10th in diameter. This apparatus screws on to any of
the aquatic boxes, also to the slider holder, figs. 25 and
26, and the false stage or black ground, figure 22, in
place of the bottom, 'p. It was invented by Monsieur
DESCRIPTION OK DR. GOFUNg's ENGISCOPK. 177
Le Baillif, at Paris ; but we have long been in the habit
of using cones for the same purpose in England.
Figure 27 is a contractor, which drops into the sink
formed in the aperture of the stage, when too large for
carrying on dissections, or other operations of a similar
nature ; it has two bayonet-catches, which secure it by
being turned one quarter round : into the aperture of
this latter piece, a small slider-holder may be advan-
tageously fixed (to be used with the Amician Engiscope
or the simple microscope), which should likewise be
made to fix to the top of the false stage, figure 22, when
its lid is removed.
Figure 25 represents a plan of the four-pillar-slider -
holder, which is by far the best contrivance hitherto in-
vented, for attaching all sorts of objects in sliders and
between slips of glass, &c. to the stage : its elevation is
shewn at figure 26, with the two pins which secure it.
In the plan are drawn the two cross connecting bars,
'u, 'u, between which and the superior plate all large
opaque sliders, &c. are placed. There is another plate
below the first : between these two a common transpa-
rent slider is shewn. The helical spring is of steel of some
strength, so that the sliders shall not be permitted to
move about between the plates too easily. The holes at
the corners of the plates which slide up and down on the
pillars, must be sufficiently large to prevent any clinging
or sticking.
Figure 28 shows a plan and profile of an adapter ,
which carries a small aquatic live box, to be used with
N
\J$ MICROSCOPIC ILLUSTRATIONS.
the wheel of diaphragms 5 it has a bayonet-catch to fix
the box securely, independent of its gravity.
Figure 29 is a frame and slip of glass for crystal-
lizations of salts.
Such is the description of an instrument which will be
found a regular working tool, either for amusement or
scientific investigation. It is not pretended (be it always
remembered) that it is a perfect or standard instrument,
but Dr. G. hopes it will be found an approximation to one.
A. P.
March 1829.
Most of the apparatus described in Chapter VI. as appli-
cable to my microscope can be applied to this. In the
instruments of this kind manufactured by me I have
made the socket at h to extend an inch or more above
the surface of the stage : this increases the steadiness of
the triangular gun- metal bar, b, which in practice is not
required to be depressed much lower than represented
in the engraving. The milled head, s, of the pinion is
made of much larger diameter than represented ; it
works against the posterior angle of the triangular bar,
and is placed at h. The fine adjustment for the focus, as
also the moveable stage described at page 105, can be at-
tached to this stage, j, and the foot of the stand made of a
solid tripod.
A. P.
May 183P.
179
CHAPTER X.
Manner of Observing with and Managing the Operative
Aplanatic Engiscope.
By C. R. GORING, M. D.
General Observations. — Select an apartment on the ground
floor, if possible, which has a northern exposure, and the
casement of which (it should have only one) is not over-
shadowed by trees or buildings, but presents a clear view
of the open sky — sky-lights are not proper for a micro-
scopic study. In such a room I would recommend you
to keep your instruments and apparatus, &c. open, and at
all times ready for observation ; but take especial care to
keep it locked, as if it was the case of your microscope, —
which, in fact, it may be termed. Have the fear of the
cat before your eyes, and also of all those busy, inter-
meddling, officious housewives, who, under pretence of
dusting, cleaning, and setting to rights, will subvert and
revolutionize the whole economy of your observatory,
and perhaps throw half your tackle behind the fire.
Never allow the apartment to be cleaned until you
have secured your apparatus. 1 think it myself a great
convenience (and I am not singular in my opinion) to
have an apartment especially devoted to my microscopes,
as much as the observatory of the astronomer is to his
IgO MICROSCOPIC ILLUSTRATIONS.
transit and circles, for then there is no loss of time when
yon wish to go to work, and you are sure to find every
thing just where you left it. I cannot be plagued by
eternally packing and unpacking my implements, &c.
but this is no rule for those who like such occupation.
Have caps to cover the objective and eye-glasses of your
instruments, and get a little nest of drawers to stand on
your table to keep talc sliders, &c. in, with a glass cover
or two (like those of watchmakers) to secure the more
delicate parts of your apparatus ; the rest will suffer no
harm from the dust. Procure a tripod stand, like those
used for small telescopes, and of such height, that when
you sit down and turn the body of your instrument
against the sky, like a telescope, the eye-piece may
present itself in a commodious position for observation.
You will also, probably, want a tripod stool to rest your
engiscope upon, when placed in a vertical posture for
dissecting and similar uses, as tables generally run too
high for the purpose, and are always more or less un-
steady. In towns the tremor occasioned by the transition
of carriages is frequently a great nuisance in the upper
stories of a house, more particularly if your mountings
are rickety and unstable.
Now, courteous disciple, I will endeavour to instruct
thee how to manage thy tackle, and will, moreover, have
the extreme complaisance to suppose thee (in all micro-
scopic matters at least) one of the aivkward squad— as
stupid as an owl, and as ignorant as a cart-horse. I will
tell thee as well as I can all that thou art to do, and all
OBSERVING AND MANAGING ENGISCOPE. 181
that thou art not to do. I will try to make thee know the
right end of thy instrument from the wrong- one ; how
to put a fly's eye before the object-glass, and a fool's eye
before the eye-piece; with many other things equally
curious, important, and interesting ; and if perchance I
shall succeed in learning thee how to deal with the
instrument under consideration, the management of all
others constructed on similar principles must be per-
fectly obvious.
It will be necessary for me to premise somewhat con-
cerning the optical part; though it is not my intention
to treat upon it in a regular way in this chapter, as a full
and particular account thereof will be given hereafter,
I shall speak of it now only as an appendage to the me-
chanical fabric of the engiscope, and the directions re-
lative to its use will be only of a general nature, but still
sufficient for practical purposes. The optical part, then,
is divided into the objective and ocular; the objective
glass is situated at 'e in figure 7, and screws on to the
neck of the body; it is always next the object of which it
forms an image or picture, which is viewed by the ocular
or eye-glass at 'c, always situated next the eye, (for be it
remembered, that in strict language we do not view the
object itself in an engiscope, but its image or picture.)
Several aplanatic object-glasses and eye-glasses ac-
company the instrument ; their powers or foci are
generally marked upon them ; but the high powers may
be known from the low ones by this simple rule, viz.
the largest object-glasses are the lowest in power, and
182 MICROSCOPIC ILLUSTRATIONS.
the longest eye-pieces, having the largest glasses in them,
are also the lowest powers. Now the total power of the
body or optical part of the engiscope, is the result of that
of its object-glass multiplied by or combined with that
of the eye-piece ; therefore the highest power will be
given by the smallest object-glass used with the shortest
eye-piece, and the lowest by the largest object-glass with
the longest eye-piece. The eye-pieces mentioned above
are all of the inverting kind, like those belonging to
astronomical telescopes ; there is, however, a pair of
erecting glasses, A, to screw into the bottom of the pull-
out tube, which, with the former, make erecting eye-pieces ;
these are used for dissecting, &c, and also for giving
very low powers when wanted below the scale of the
weakest inverting ones. The use of all these I shall
shew in their proper places. Each object-glass combines
with each eye-piece, whatever their number may be,
according to the fancy of the observer, but the power
which results from the combination can only be known
by trial, and should be given by the maker of the instru-
ment, in a written paper.
The object-glasses are frequently made to combine
with each other. An increase of power is obtained by
the elongation of the body, effected by drawing out the
tube, 'c : whenever the length of the body is doubled, for
example, the power is also doubled {ceteris paribus).
In winter it will be proper to cause the instrument to
be slightly warmed at the fire before it is used, until it is
of about the same warmth with the human body, other-
OBSERVING AND MANAGING ENGISCOPE. 183
wise the perspiration from the eye will be perpetually
condensing on the eye-glasses, &c. and greatly impede
vision.
Always begin to examine your object with the lowest
power you have, unless it is very minute ; it may be laid
down as a general rule, that large objects require low
powers, and small ones high powers ; that the low
powers show the whole or general view of an object, and
the high ones only its parts in succession.
Never use high powers unless absolutely necessary ;
for as the power increases, so does the difficulty of
finding the object, and of adjusting the focus. The
colours also grow fainter and more diluted, and the
shades darker and darker, until all ease and satisfaction
in observation, together with all certain vision, fade
away, and so very small a portion of the object is seen,
that it is difficult to know what we are looking at. Re-
collect that a really good aplanatic object-glass shews every
thing ivith very low powers ; in fact in this property its
goodness and beauty consist : do not plume yourself,
therefore, upon having an instrument which shews
objects with very high powers, but with very low ones.
Where, however, from the minuteness of an object, it
becomes really necessary to use a high power, always
select a small deep object-glass, and use it along witb a
shallow or long eye-piece, in preference to using an object
glass of low power, with a short or powerful eye-piece,
for magnifying power is much more valuable and effec-
tive when derived from the object-glas^ than from the
184 MICROSCOPIC ILLUSTRATION'S.
eye-piece (this is a subject which I shall recur to
hereafter.)
When you clean the eye-glasses (a point of great im-
portance to pure vision) do not remove more than one
at a time, and be sure to replace it before you begin
with another : by these means you will be sure to pre-
serve the component glasses in their proper places :
recollect that if they become intermingled, they will be
useless. Keep a piece of well-dusted chamois leather,
slightly impregnated with some of the finest putty or
crocus powder, in a little box to wipe them with (for it is
of consequence to preserve it from dust and damp),
the former will scratch the glasses, and the latter pre-
vent you from wiping them clean. As to the object-
glasses, endeavour to keep them as clean as possible
without wiping, and merely use a camel's hair pencil to
brush them with ; for wiping them hard with any thing
has always a tendency to destroy their adjustment, unless
they are firmly burnished into their cells.
Now I shall suppose that you want to view some trans-
parent inanimate object mounted in a slider. There are
several ways of doing this, according to the position in
which you choose to preserve your instrument, whether
directed upwards towards the sky, horizontally, or ver-
tically, looking downwards, &c. The first is the best
method for direct day-light ; the second, for lamp or
candle-light ; the last is the worst of all for either, and
should not be resorted to when the others can be used.
There are, however, intermediate positions between the
OBSERVING AND MANAGING ENGISCOPE. 185
horizontal and vertical ones ; say angles of 40 and 45
degrees, which are comfortable and convenient for the
observer, though, 1 think, unfavourable to the action
of the illuminative part of the instrument. I shall pro-
ceed to give directions, on the supposition that you wish
to see in the simplest and best possible manner.
1st. Manner of mounting for viewing inanimate trans-
parent objects by pure intercepted day-light. — When the
instrument is first removed from its case, the circular
bar, c, will be locked fast into the upper or longest leg,
by means of its projecting pin; it is loosened by drawing
the internal tube of the pillar a little out, for which pur-
pose, grasp the ball and socket in one hand, and the legs
in the other: by pulling in opposite directions, the inner
tube will be detached, and the pillar heightened in any
degree requisite for observation, at the same time the
bar will be left at freedom to move in any direction by
means of the ball and socket : immediately underneath
the pillar is an adjusting screw, e, by means of which the
pillar gains the support of a fourth leg, and is rendered
incapable of springing ; it can be used when great stea-
diness is required : it should but barely touch the table
or stand on which the engiseope is placed.
Having then spread out the legs, and arranged the op-
tical part according to the preceding directions, attach
the slider-holder, fig. 25, to the stage. This is done by in-
serting the projecting catches into the nicks, and turning
it one quarter round : this fixes it fast, so that it cannot
186 MICROSCOPIC ILLUSTRATIONS.
fall out whatever may be the position in which it is
placed : pass the slider between the plates until the ob-
ject appears within the aperture; slacken the pinching
screws of the split sockets belonging to the mirror and
condensing lens (if necessary), and turn them one quar-
ter round, so as to be out of the way of the body, or they
may be removed altogether, by sliding them off the bar ;
then, by means of the double action of the ball and
socket, elevate the bar, until the instrument, when
placed on its tripod stand, comes into the position of a tele-
scope directed towards the heavens, at any angle you
please. In fine weather, it will not be improper to let
down the upper part of the casement; some micro-
scopists have recommended us to select a ivhite cloud, if
possible, to furnish our transmitted light ; I think myself
that the blue light of a clear atmosphere is preferable,
especially for test objects. The ball performs the office
of a cradle joint, by being moved up and down in the
quadrant slit of the socket. Thus, if you wish the bar to
point upwards, and the ocular end of the body down-
wards (as will be the case in the present instance), make
the following arrangement :— Move the neck of the ball,
by grasping the bar until it is about half way between
the upper and lower end of the quadrant slit, {just as if it
was a common cradle joint) : the body thus forms an angle
of about 45 degrees, and will be in the required position
(but unless the motion now to be described has been
previously accomplished), in a direction directly opposite
to that now required, for you ivill only be able to observe
OBSERVING AND MANAGING ENGISCOPE. 187
with it by looking downwards, whereas you are to look
upwards. To effect the object at present in view, turn
the ball completely round in the plane of the bar, until the
end of the bar comes into the place of the eye-piece.
The instrument is then fit for use (at least when placed
on its tripod stand and directed towards the sky) ; re-
member, that by the motion of the ball as a cradle joint,
conjoined with the rotatory movement natural to it, every
possible position is attained. All you have now to do
will be to adjust the focus, and to bring the body to bear
on the part of the object you wish to see. The adjust-
ment of the focus is accomplished by means of the milled
head, s, and the traversing motion of the body is go-
verned by the rack- work at v, coupled with the rotatory
movement on the top of the bar, which is regulated by
the milled-head at z ; the method of managing this part
of the instrument will be gained with the utmost facility
by a little practice. In the present case it will not be
very necessary, as you may move the object about at will
with your hands between the plates of the slider-holder.
When you look through the instrument, be sure to
place your eye quite close to the eye-piece, otherwise
the whole field of view will not be visible, and note,
moreover, if you see a round disk of light, at least when
the object is not in the slider-holder; if you do not, it is
a sign that something is wrong; perhaps the body is not
placed directly before the aperture of the slider-holder,
or may not be truly directed towards the light, &c. It
only remains for me to observe, that the method of using
188 MICROSCOPIC ILLUSTRATIONS.
the instrument just described, is by far the best and
simplest with which I am acquainted for all sorts of
transparent objects, and should, therefore, always be
used when practicable ; and this observation applies to
all sorts of microscopes and engiseopes. Occasionally,
however, the weather is so dull and gloomy, that we see
better by artificial light : I therefore now give the
2nd. Method of mounting for viewing transparent objects
by artificial light. — Setting out on the supposition that
the instrument has been just removed from its case, and
is in the position given in the plate, proceed as follows : —
Place it on a table ; detach the bar from the front leg,
as before ; move the mirror and condensing lens to one
side ; then turn the bar round till it assumes a hori-
zontal position, keeping the neck of the ball at the bottom
of the quadrant slit, in the position in which it is repre-
sented in the drawing : its rotatory action is the only one
at present required. This arrangement will leave the
space, both behind and before the stage, open for the in-
troduction of a lamp or candle, &c. The condensing
compound lens, f, attached to the body, together with the
plane-convex one, n, under the stage, and the mirror,
must remain inert and unemployed, in this as in the pre-
ceding mode of observation, and may be removed alto-
gether. Adjust the height of the instrument to suit that
of your light and eye, by drawing the tube of the pillar
in or out : place your light centrically behind the aper-
ture of the stage, at two, four, or six inches distant from
OBSERVING AND MANAGING ENGISCOPE. 189
it, according to the strength of the illumination required,
observing always to preserve a perfect round disk of
light in your field of view, and every thing goes on as
before, the candle or lamp supplanting the day-light.
You may, if you please, tilt the instrument a little out of
the horizontal plane, for convenience of observation.
3rd. Mode of mounting for viewing diaphanous bodies
by refected day-light, either in a horizontal or vertical
position. — For the horizontal position every thing is ar-
ranged in the same way as when artificial light is em-
ployed ; only, now the oval mirror comes into use, which
must be placed truly in the axis of the body, and of the
aperture in the stage. For this purpose, cause the mark
on its split socket to tally with the line drawn on the bar,
and then clamp the split socket tight by the screw, m :
then, having first removed your instrument out of the
direct light proceeding from the window, by placing it
in the middle of the apartment, proceed to reflect the
light given by the said window into the body of your in-
strument, as follows. I must premise that it will be
necessary that the engiscope should so present itself to-
wards the window that its pillar and bar should not im-
pede the light : thus, supposing the window is on your
left hand, the pillar and bar must be on your right, and
vice versa, so that nothing shall be bettoeen the window and
the mirror. Observe, that a direct lateral position of the
window is the most convenient and manageable. Then,
by means of the milled head, draw the mirror round on
190 MICROSCOPIC ILLUSTRATIONS.
its axis, at the bottom of the arm p3 until it fronts the
casement; then all that is requisite is, to turn the milled
head, r, and along with it the mirror, round, until its
light fills your field of view ; which will be at an angle
of about forty-five degrees, if the window is directly op-
posite the mirror, and your bar parallel with it. You
may now, if you please, use the condensing lens, n, but
I do not recommend it, as, along with an increase of
brightness, it generates a degree of confusion and nebu-
losity. If employed, see that it is clamped tight into its
true position on the bar. Like the mirror, it should be
as close to the stage as possible.
If you wish to be exactly acquainted with the colour of
transparent bodies, use the plaster of Paris side of the
mirror to reflect the light of the sun, in an apartment
exposed to it. With this intent, place the instrument on
a table on which the sun falls, in such a manner, how-
ever, that it shall only impinge on the plaster, and leave
the rest of the engiscope in shade ; then proceed with it
as if it were day-light. This, in my opinion, is the only
way in which the light of the sun can be employed with
advantage for illumination, and it brings out colours
with the most perfect fidelity.
When the instrument is used in the vertical posi-
tion, it is, of course, in the altitude represented in the
plate, and is governed precisely in the manner just de-
scribed. I do not like this position at all : it should, I
think, only be used with bodies which must be confined
to the stage by their gravity alone, which case may some-
OBSERVING AND MANAGING ENGISCOPE. 191
times occur; but I have made most ample provision for
presenting all sorts of objects in any position, without re-
gard to their gravitation, by means of the aquatic wet and
dry glass boxes, and the slider-holder, &c. I think that
the practice of poring downwards (the ordinary way of
observation with microscopists of the old school,) is pe-
culiarly detrimental to the head and eyes, having a great
tendency to determine the blood to them. We never
hear of astronomers, ivho are perpetually looking upwards,
having their sight injured, like observers with microscopes,
though they have to look, if possible, still more stead-
fastly and intently than the latter, with the highest
powers. I had nearly forgot to mention a circumstance
very necessary to be attended to in the management of
the mirror; it is this, — to keep the milled head, r, inva-
riably outwards. It is not made to travel completely
round, nor is it necessary ; for every possible position
required for practical purposes can be attained withou t
its traversing more than the half of a circle, by reversing
the superior or inferior end of the ellipse, according to
circumstances. Thus, supposing there were two win-
dows in an apartment; one on the right, and the other
on the left of the instrument, it would command either,
without revolving on its inferior axis, merely by being
tilted on the right or left side.
Way of viewing Crystallizations of Salts and various
Chemical Actions. — Use the mounting (No. 2); screw on
the lengthening piece, "i, and attach the diagonal boot
192 MICROSCOPIC ILLUSTRATIONS.
(fig. 16) to it. By means of the wheel and endless screw
let down the arm of the instrument till the body shall be
considerably below the aperture of the stage ; then take
off the lid of one of the aquatic boxes, and fix the other
part, first warmed at the fire, upon the stage ; which
turn round on its pivot until its surface with the box
shall point downwards ; then insert a drop of the salt to
be viewed upon the inferior glass of the box (now, by
virtue of its position, the superior one); turn the boot
round on the lengthening piece until its projecting cone
shall look upwards, and adjust the focus by means of the
wheel and endless screw, which noiv performs this office,
while the rack-work used under other circumstances, for
the same purpose now only gives a traversing movement.
Many chemical actions, between various bodies, both
fluid and solid, may also be viewed in this way. More-
over, crystallizations, &c. can be seen under any of the
usual modes of mounting, by placing the salts or other
bodies, between the glasses of the aquatic boxes, with
the closed or pierced lids, as the occasion may demand ;
only, whenever there is evaporation or evolution of gas,
remember to employ the pierced lids.
I think, nevertheless, that the best way of viewing salts
is to use the glass slip, with its frame (fig. 29), and
merely to rub the liquid salt over its surface, allowing it
to drip a little at an angle of 45, before it is placed in
the slider-holder. The glass must not be ivarmed in this
method; and the salt must be allowed to crystallize
very slowly, in its own natural way. By this process,
OBSERVING WITH AND MANAGING KNGISCOPE. 193
though somewhat tedious, none but the veritable micro-
scopic crystals are obtained. Deliquescent salts, in damp
weather, can, however, hardly be brought to consolidate
in this way.
I hope the description of the method of management
is now tolerably complete, as concerns transparent inani-
mate objects ; but the method of dealing with living ones
requires some illustration.
4th. Way of Mounting for Transparent Living Objects. —
These are not seen well by artificial light, as I have
already observed, their internal machinery being more
or less confused by it, whether its rays come diverging,
converging to a focus, or parallel.
It will be rather difficult to get a power low enough,
with the present instrument, to obtain a general view of
a number of the larger aquatic larvae ; for I do not think
the present engiscope will carry an object-glass of longer
focus than two inches ; which, with the lowest inverting
eye-piece, will be fully twice too high — (for, be it ob-
served, the lower the power is the more of an object it
will include in the field of view, and the higher the less);
but, with the erecting eye-piece thrust pretty far into
the body, a power will be obtained that will easily in-
clude a space of one and a half, two, or even three
inches; therefore use the erecting glasses A, screwed
on to the bottom of the internal tube of the body, and
draw it in or out, until it just takes in the area of your
o
194 MICROSCOPIC ILLUSTRATIONS.
largest aquatic live-box, and use the first or third way of
mounting.
The method of using the aquatic live-box is as follows : —
Take off the lid, applying your finger to the hole in it, or
stop it up, pro tempore, with a bit of wax ; then pour
in some water to the depth required, and insert your
larvee, and apply the inner part to it, observing still to
keep the lid undermost : having slid it on far enough to
keep the water from escaping, place the box in such a
position that the hole in the lid shall point upwards ; then,
by squeezing the lid on further (having, of course, first
removed your finger orbit of wax from the hole), you
may expel all the air, and as much of the water as may
be superfluous. It is now fit for use (for the pressure of
the atmosphere prevents the water from coming out of
the hole) by being placed in the aperture of the stage,
and turned one quarter round. A single drop of water,
containing animalcules, may be placed between the
glasses of the smaller boxes ; and, if the tubes are made
air-tight by a little grease, and the hole stopped up, may
be kept for wTeeks together without evaporating.
If very delicate and exceedingly transparent animal-
cules are to be examined, use the adapter (fig. 28), with
the smallest aquatic live-box mounted upon it, and se-
cured by the bayonet-catch : let it be placed between the
connecting cross-bars, 'u 'u, and the superior plate of the
slider-holder, which arrangement permits the adapter
to be moved about: screw the wheel of diaphragms
(fig. 24) on to the bottom of the slider-holder, and sec
OBSERVING WITH AND MANAGING ENGISCOPE. 195
that the body of the engiscope is truly concentric with
the hole or diaphragm ; otherwise you will have no light.
Recollect, that the body of the instrument must now be
stationary, and that you must move the slip about with
your fingers. Whenever the diaphragms are employed, the
body must be a fixture, or nearly so.
A very useful way of observing aquatic insects and
larvae is by means of the direct or diagonal boot drawn
over the lengthening piece, 'i, of your object-glass, which
may then be inserted into the reservoir in which they
are kept. The method of mounting is as follows : — Un-
screw the body from the arm, iv, and attach fig. 15 or 16
to it, instead of its usual neck : see that the plane-glass at
their ends is as far removed from the object-glass as pos-
sible {for the less water you have to look through the more
distinct will be the vision) ; detach the stage from its pivot
by slackening the screw, I, and clamp it tight on the
lower pivot, i, having previously removed the con-
denser, n, altogether : then place the glass vessel on the
stage, which must be truly horizontal, and clamped tight
by the pinching screw, I .- insert the body into the reser-
voir, by rescrewing it, with its new appendage, on to the
arm, iv, again. If you want to observe laterally, or to
take a periscopic view of the contents of the vessel, use
the diagonal boot in place of the direct one ; and, by
turning it round on the lengthening piece, any object
situated on the sides of the vessel, such as polypi or vor-
ticelhe, may be observed without disturbing them. The
object-glasses apply either to the ordinary neck of the
196 MICROSCOPIC ILLUSTRATIONS.
body, or to the lengthening piece over which the boots
slide. Dissections may frequently be carried on under
the surface of fluids by means of these boots, with great
effect, which can hardly be accomplished in the common
way.
Whenever the instrument is in a vertical position (as will,
of course, be the case in the present instance,) or when it
is not far off" from it, the lever y may be used with great
advantage. In observing live subjects it is peculiarly use-
ful, for it enables us to follow their movements much more
rapidly than can be done by means of the wheel and end-
less screw ; and the double motion of the arm being, by its
assistance, governed entirely by one hand, the other is left
at liberty to adjust the focus (which is, of course, perpe-
tually changing, according to the motion of the insects
observed) ; it is attached to the pinion on either side of
the rack-work, according to circumstances, by being
pushed on the square projecting pin. The wheel must
then be detached from the endless screw, by slackening
the clamping screw, 'b, and drawing the piece which
carries the said endless screw backwards away from the
wheel, causing it to traverse over a portion of the arc
which it forms on its pivot, and fixing it afresh, so that
it shall not catch the teeth of the wheel : the arm then
moves freely round on the top of the bar, and is subservient
to the action of the lever, the milled head of which operates
upon the pinion in place of the ordinary one, and is
governed by the thumb and index. finger ; while the others
OBSERVING WITH AND MANAGING KNGISCOVE. 197
act upon its extremity, and give the rotatory movement
which was before performed by the wheel, &c. More-
over, whenever the lengthening piece is in use for trans-
parent objects not contained in fluids, the shade (fig. 18)
may be employed. It slides down completely over the
object observed, and guards it effectually from all rays of
light not transmitted through it, so that it is observed purely
as a diaphanous body, and not partially also as an opaque
one (as is frequently the case with transparent objects
treated in the common way). This piece of apparatus is
of much use in verification.
The stage may, moreover, be removed altogether; and
the bar being in the horizontal position, the vase may be
placed on a proper support in its stead, and observed
from without as well as from within.
5th. Method of mounting the Diamond and Sapphire
Microscopes for Transparent Objects. — When the use of
the engiscopic part of the instrument is thoroughly
attained, nothing can be more easy than the management
of these. All that is requisite is to unscrew the body
from the arm ; and by detaching the teeth of the wheel
from the endless screw, according to the directions already
given, to reverse the ends of the arm, so that the micro-
scope shall come into play ; whent he rotatory movement
must be again secured, by bringing the endless screw in
contact with the wheel, and clamping it tight : thus the
instrument becomes converted into a simple microscope
of the first quality, which is to be used exactly as the
198 microscopic illustrations.
engiscope was : I can give no better directions concerning
it. The sapphire and diamond lenses have their own
peculiar settings in a species of dish or cup, which is
attached to the arm by being* thrust into the hole at its
extremity. The superior cohesion of the precious stones
admits of their being burnished into a cell, which is again
fixed into the setting. This arrangement allows the
lenses to be shifted about without difficulty, or risk of
losing them. If they are plano-convex, as they should
be, another advantage results, which is, that they may
be used either with their flat or convex side towards the
object, according as great distinctness, or a large field of
view, may be required (for you cannot have these quali-
ties combined). Remember, therefore, if you want a
large field of view, and do not, at the same time, require a
large aperture, united with great distinctness, to place the
lens with its flat side next the eye. If, on the contrary, you
must have a very large aperture, conjoined with the utmost
possible degree of distinctness, then place the convex side
next your eye. The aplanatic lenses should also have set-
tings on which they can be screwed at pleasure, to be used
as simple microscopes. If, at any time, when bodies are
merely laid upon the stage, and confined to it only by their
gravity (the stand being used vertically, as in dissections,
for example), the face should come into too close contact
with the stage, the apparatus (fig. 21) must be used,
which is inserted into the aperture, like the live-boxes and
slider-holder : the object being laid upon it, due space will
be afforded for the nose, and the breath will be less likely
OBSERVING WITH AND MANAGING ENGISCOPE. 199
to steam the lenses. The arm, w, is made to turn round
in any position most convenient to the observer. The
adapter (fig-. 28), which is to be used between the bars of
the slider-holder, to carry a small aquatic live-box, or the
like, affords another species of convenience of a similar
nature, and serves to elevate the face of the observer
above the stage.
Opaque Objects. — Opaque objects seldom require such
high powers, or such large apertures, as transparent ones.
Their colours are best brought out by daylight, natural
or condensed ; but artificial light, perhaps, shews them
best in all other respects.
They should always be viewed upon a black ground of
some description. The more sombre, and dingy, and
faint, their tints are, the greater need there is of a black
ground to stifle all heterogeneous light.
As they only reflect or radiate light, a much stronger
illumination is requisite for them than for diaphanous
bodies, which almost always transmit a great deal more
light than opaque ones are capable of reflecting. More-
over, they seldom present flat surfaces, as most pellucid
bodies can be made to do. This, when the power is con-
siderable, causes one part of the object to be indistinct,
while another is seen accurately : this must always be
allowed for. A very perfect1 instrument can only have
one point in focus at once, and, consequently, can only
shew one point distinctly at once, all the rest not on the
plane of the focus being confused.
200 MICROSCOPIC ILLUSTRATIONS.
The direct light of the sun is utterly improper for
exhibiting- opaque bodies, being polarized and decom-
posed by them, so as to give rise to all sorts of optical
deceptions : neither can it be modified or dulled by
refraction through rubbed glass, or any sort of semi-
pellucid substances, and thus rendered fit for use : by
reflection from white toipolished surfaces it may, but it is
then no stronger than the light of the atmosphere.
6th. Method of observing Opaque Objects by Day-light,
plain or condensed. — Employ the mounting (No. 2) recom-
mended for transparent objects by artificial light.
If your object is contained in a slider, insert it into the
holder in the usual manner : turn your back diagonally
towards the window, and place the engiscope on a table,
in a convenient position for observation in that direction,
so that the light of the window may fall full upon your
object, without being intercepted by your head : the
nearer you are to the window the better, provided its
direct light does not get into your eyes. You then pro-
ceed to the adjustment of the focus, &c. as before de-
scribed. If your power is considerable, or the day dull,
you will require a condensed light : to obtain it, attach
the condenser, '/*, to the neck of the body, by means of
its clamping screw and split socket, 'g ; unscrew the
double convex lens from the other, and remember to use
only the piano- convex, with its plane side presented
towards the light, and its convex side towards the object :
slide it up or down upon the neck of the body; and adjust,
OBSERVING WITH AND MANAGING KNGISCOPK. 201
also, by the help of the joint, v, until you get a good
spectrum of light upon your slider. (It will be well, in
the first instance, to form an image of the window upon
your object, and then to push the illumination a little
closer to it, so as to obliterate the image.) You will in
this way get the maximum of brightness : — The crown of
the convex side of the bull's eye, or condenser, when
properly adjusted, will be about an inch, or an inch and
a quarter, from the object.
If you think it more commodious, you may attach the
condenser to the stage, instead of the body — (only, in this
case, if you move the optical part, you will lose your
light). To effect this, remove the setting of the lens
altogether from the split socket, by unscrewing the
joint, v, and fix it afresh, by means of its screw, into the
square bar, fig. 14, which insert into the square hole in
the stage. The adjustment is effected now by pushing
the illuminator up and down in the stage, combined with
the motion of its joint, r, as before. I think, however, it
will be found advisable only to attach the condenser to
the stage ivhen artificial light is employed ; for, in this latter
case, the weight of an additional lens is applied to the
condenser, which might overload the body, if depen-
dent from it.
If you wish to view opaque terrestrial living objects,
put them into the suitable live-boxes, with the pierced
covers, to admit air. These said boxes, with one or the
other of their lids, may be used to hold nearly any
object.
202 MICROSCOPIC ILLUSTRATIONS.
7th. Method of observing Opaque Objects by Artificial
Light, either plain, condensed, or reverberated, by Silver
Cups. — Use the mounting (No. 2), as before: close the
shutters of your apartment, if you mean to observe in this
way in the day-time : procure a telescope candlestick, or
one which has an arm moving up and down upon a bar,
so that it can be adjusted to any height as a candle burns
down — (the sliding-tube of the pillar will, in some mea-
sure, serve this purpose, if you have not a proper candle-
stick), and get a wax taper, or, what is better, a piece of
old rushlight, to afford your illumination. Don't laugh !
but do as I bid you : and, moreover, a pair of scissars, to
trim it. A piece of rushlight (please your worship) well
trimmed, gives a remarkably steady light, without flaring
or flickering , and is just as intense as that afforded by oil,
or tallow, or gas itself, burnt in any other way. The
intensity of the light is the thing wanted, not the quantity.
Perhaps a wax rushlight might be an improvement. Now
this rushlight, adjusted- to the proper height, is to be
placed before your stage, and as near to your object and
object-glass as may be, without burning them : but you
must take especial care that its direct light does not get
into the body of the engiscope, or it will utterly destroy
all distinct vision : on this account it must be always
placed a little on one side of the objective : and if the
focus of the said object-glass is longer than half an
inch, it will be highly advisable to use a conical
shade (fig. 19), drawn over it, reaching almost to the
object itself; which will, moreover, always be some
OBSERVING WITH AND MANAGING ENOISCOPE. 203
security against burning it, or injuring the object-
glass itself. The object, if below a certain size, will
of course be seen upon a ground of some sort, and this
must be a black one: if on a slider, it must be gummed
upon black paper ; or, if mounted upon a cork cylinder,
having a pin thrust through it, the surface of the cylinder
must be blacked with lampblack and glue, before the
object is applied to it : but if it is of a nature to be held
by the nippers, Mr. Lister's black ground (fig. 22) must
be employed to bring it out in true relief; for it is far
blacker than any other, and stifles all heterogeneous
light much more perfectly. This is attached to the
stage in the same way as the live-box or slider-holder ;
and is, in fact, the same piece of apparatus which con-
stitutes the false stage for the simple microscopes, and
for dissecting ; with the top and bottom, 'u, 'p, applied
in their proper places, to close it up. In the present
case, its dark abyss is to form the ground against which
the object is examined. At the other end of the needle
is a piece of cork, contained in a bit of brass tube. This
is to receive the pin by which insects are retained in
their drawers in entomological cabinets, which can thus
be taken out and examined without injury ; more espe-
cially if the pins have been thrust through them diago-
nally, which is a great convenience when applied to the
microscopes, as it allows their backs and bellies to be
freely presented to the action of the object-glass. The
nippers, seen of their natural size at fig. 23, are drilled
through at .9, so as to lay hold of the head of a pin, and
204 MICROSCOPIC ILLUSTRATIONS.
retain it firmly, so that it can be twisted about in any
direction, without risk of detaching- it. This will be
found a most useful contrivance for holding the cork
cylinders, and all objects ivhat soever mounted on pins.
The swivel which carries the nippers, &c. is thrust into
the arm, and in that manner used, as shewn in the plate.
The mode of observation by plain artificial light
corresponds with that by plain daylight. It is one of
the simplest and best ways of viewing opaque objects ;
and the contrast of the strong divergent lights and
shadows cast by the rushlight, brings out, and enables
us to comprehend, the forcshortenings and perspective
of the complicated details frequent in irregular opaque
subjects, and thus to verify their true nature, construc-
tion, and relative position, much better than, I think,
any other sort of illumination.
Never forget that, when observing with the candle
before the stage, you must hold your breath, or have a
handkerchief tied over your mouth : a single puff is all
that is necessary to cause the flame of the light to play
over the object and destroy it (and thus in fits of absence
have I destroyed many valuable ones). What renders a
rushlight so useful is, that it will not, of itself, flare over
your object : it can, moreover, on account of its small-
ness, be got closer to an object with impunity than any
other artificial light ; and thus, in fact, gives the most
intense sort of plain illumination ; for the intensity of
light decreases according to the square of its distance
from the object.
OBSERVING WITH AND MANAGING JSNGISCOPE. 205
When observing faint, sombre, and dull opaque ob-
jects, especially if high powers are used, a vast increment
of apparent brightness is obtained, if all light is excluded
from the eye, save that of the visual pencil. Thus, it
will be found a great assistance if a large blackened
pasteboard shade, nearly a foot in diameter, is made to
fasten upon the eye-piece, and thus completely to ex-
clude the direct light of the candle, &c. ; or still better,
if a black hood, like those used by astronomers, is made
to cover up the face completely, but with an aperture for
the body of the instrument. Such an arrangement also
saves us the trouble of shutting one eye; and the en-
largement produced in the aperture of the iris, by keep-
ing the eyes in the dark, enables the faintest rays to
affect the retina.
Condensed Artificial Light is procured by the action
of the double illuminator, 'f; whenever it is used by
lamp or candle-light, the double convex must be screwed
on, still preserving the convex side of the piano, or bull's
eye, next the object. The split socket must be clamped
tight in such a position on the neck of the body, that it
shall present the face of the illuminator in a lateral
position relative to it, so that the rays of the candle, &c.
shall fall conveniently upon it ; its distance from which
should be about an inch and a half, and its distance from
the object should also be about an inch, which will give
the maximum of illumination, with a large spectrum, so
as to illume a considerable space. I think, whenever
206 MICROSCOPIC ILLUSTRATIONS.
this condenser is used, the flame of an Argand lamp
should be employed, shaded, however, by an external
copper tube, with an aperture in its inferior part just
large enough to expose the flame, placed over the usual
glass one. This will give increased effect and splendour
to the object, by preserving the apartment in gloom, and
thus allowing the iris to expand itself.
I do not think a more intense light is got with an
Argand lamp than with a rushlight, but certainly a
far greater quantity of it.
Silver Cups, or Specula, afford a very brilliant and
intense light, almost ivithout shadow, because it plays
vertically upon the summit of an object, like the sun of
tropical climates. This is the only species of illumination
which will bring out many opaque objects properly (a
fly's foot, or human hair, for example) ; but for others,
requiring shade for their verification, it is altogether
improper. (The markings on the scales of butterflies,
&c. are a good illustration of this position.)
Each object-glass must have a cup attached to it ca-
pable of adjustment, by being moved up and down upon
the tube in which the object-glass is set, so as to cause the
focus of the latter to coincide with that of the cup, (the
maximum of brightness cannot otherwise be easily
attained) . The object must alivays be held by the nippers
or mounted on a cork cylinder, when it is to be illuminated
by cups : when the nippers only are employed, the disk,
7, must be placed between them and the illuminating
OBSERVING WITH AND MANAGING ENGISCOPK. 20/
lens, &c. so as to prevent any false light from getting
into the ohject-glass, and also to furnish a black ground.
Remove the bottom of the black box, 'p, and fix the
condenser, n, in such a position, by means of its tight-
ening screw, that its convexity shall be inserted into the
bottom of the said black box, which will be found its
best position either for day-light or candle-light. The
cngiscope must then be placed on the tripod- stand
mounting, No. 1, and directed against the sky, (the
best way, perhaps, of using the cups, with da;/- light),
or it may be used in an horizontal or vertical position,
and the light reflected by the oval mirror; but when
artificial light is preferred, use the mounting No. 2,
and place an Argand lamp about an inch and a half
from the condenser, n, taking care that its flame is con-
centric with it, and a most intense illumination will be
procured, even with powers equal to the l-60th of an
inch focus. Cups, when properly managed, give a
brighter light than can be procured by any other
means. They may be used without the assistance of
the condenser, but, of course, in this way give a much
more feeble light.
Please to remember that the condenser under the
stage, and that represented attached to the body, are
expressly and exclusively devoted to opaque objects.
8th. Mounting for Dissections, §c. — Dissections are ge-
nerally performed on opaque subjects, though it may be
sometimes necessary to dissect transparent ones also.
208 MICROSCOPIC ILLUSTRATIONS.
The erecting eye- piece must, of course, always be em-
ployed, by sliding it up and down in the body ; with
various objectives the power may be made gradually to
advance from a mere nothing- up to the l-20th of an inch
(which I conceive to be the utmost which can be used),
and still allow sufficient space between the object and
the object-glass for the anatomist to manage his imple-
ments, and to procure the necessary illumination.
Mount the engiscope in the vertical position, and see
that the bar is locked fast in its front leg, to give the
utmost degree of stability ; place it on the tripod stool,
before recommended, with the front of the stage before
you, and the pillar next to the window — (a diagonal po-
sition for yourself and the instrument relative to it, will
be most convenient, to allow the light to fall freely on
your subject.) Use the single condenser, n, to furnish
your light, if necessary ; it may be moved round the
neck of the body, to suit your convenience. You may
also employ the lengthening piece,'/, if you please, which
will allow you to fix the stage on the pivot and sliding
socket, i, and give a lower position for it. If you use the
latter, see that it is clamped very fast, that it may not
give way with the weight of your hands.
If you do not find it advisable to employ the false stage,
fig. 22, which procures a separate rest for the little
fingers, while the thumb and index finger operate, drop
the piece, fig. 27, into the aperture of the stage, and fix
it by turning it one quarter round. Then place the
piece of cork or wood, he. on which you dissect in the
OBSERVING WITH AND MANAGING ENCISCOPE. 209
smaller aperture of this, and proceed. I should recom-
mend you to get the leaves of two Pembroke or other
tables placed on each side of you, to rest your elbows
upon at pleasure, and likewise to procure several pieces
of board, about one and a half inch thick, to place under
the instrument, to depress or elevate it without the help
of the slide in the pillar (which, when called into effect,
always unlocks the bar.)
Your operations can always be carried on under the
surface of liquids, by the help of the direct or diagonal
boots.
When you wish to get at the side of your subject with
out disturbing its surface, mount in the position, No. 2,
and turn your stage round on the pivot, i, until it comes
to be in the plane of the bar : every lateral view can then
be obtained at pleasure, by turning the object round,
and you can operate in this position as well as in the ver-
tical one. You may also, by help of the ball and socket,
tilt the body at any required angle, and still adjust the
stage to the horizontal position, as before, taking care to
pinch it fast by means of the screw, I, before you begin
to work again.
There are no tools for dissection equal to very fine
scissars, — they always cut without dragging or tearing ,
there is, however, the greatest difficulty in procuring
them. The Sheffield workmen are the oidy ones capable
of making them sufficiently delicate. Miniature scissars
have been made only half an inch in length quite perfect J
now, a pair constructed with blades like these, but in
210 MICROSCOPIC ILLUSTRATIONS.
other respects like those for some operations on the eyes,
(i. e. without bows), having one arm inserted in a long
handle, and the other left short, playing against a feeble
spring to keep it open, is the sort of tool required. It is
held like a pin, and cuts by the pressure of the index
finger on the short arm. You may, of course, dissect
with simple microscopes of loiv powers as well as with the
engiscope, but the present stand is not so well adapted
for them as a separate one would be.
9th. Mounting the Diamond and Sapphire Microscopes
for opaque objects. — It is one of the vices of simple mi-
croscopes that they can only shew opaque objects with
cups — at least if their powers exceed one quarter of an
inch. The lower foci shew opaque objects admirably
with day- light, the stand being in the vertical position.
When used for plain day-light in a horizontal one, all
that is necessary is to assume such an attitude relative to
the window that the head shall not intercept its light.
For example, if you sit with the bar horizontal and pa-
rallel with the window, the light will naturally fall be-
tween the stage and the magnifier upon the object. When
cups are employed, they act precisely like those attached
to the engiscope, and magnifiers thus mounted are
managed in the same way.
10th. The Amician Catadioptric Engiscope is attached
to the present stand by means of the arm, fig. 20, and is
managed precisely on the same principle as the refracting
OBSERVING WITH AND MANAGING ENGISCOPK. 211
aplanatics. The body turns round upon a swivel, by
means of the pinching screw, to suit the convenience of
the observer ; and the only real peculiarity in observing
with the reflecting engiscope is, that the optical part is
always at right atigles to that of the refracting one in any
given mode of mounting or observation — just as the eye-
tube of the Newtonian telescope is relatively to that of a
refractor, cat eris paribus ; but this instrument, as well as
the simple and compound microscopes, are probably best
on their appropriate stands, of which full and particular
descriptions will be given hereafter*. It is only for the
sake of those who should like to have the three instru-
ments jumbled together, that they are adapted to the
same stand in the present case.
Courteous reader, I have endeavoured to supply the
place of a viva voce lecture on the instrument, and to in-
fuse into thee such knowledge as I possess, touching
the management of the aplanatic engiscope, &c. The
directions given will, I hope, be found more explicit,
clear, and intelligible, as well as more full, particu-
lar, and diffuse, than any others hitherto given in print.
Vale ant quantum valere possunt. By their assistance thou
shalt be enabled to enter into a course of researches very
nearly as profitable to thyself and fellow creatures as if
thou wert engaged in the sublime and important occu-
pation of determining whether the small star of e Bootis,
is of a greenish blue, or bluish green ; or whether some
nebula is very gradually or very suddenly much brighter
in the middle.
* Vide Micrographia, chap. i.
APPENDIX.
No. 1.
On the Optical Phenomena of certain Crystals.
By H. F. TALBOT, Esq. F.R.S.*
Some time ago I had the honour to communicate to the
Royal Society an account of my invention of the pola-
rizing microscope. This instrument possesses so great
a power of developing the internal structure of trans-
parent bodies, even in their minutest visible particles,
that I feel confident the employment of it will lead to
many new and interesting results. At present I mean
to confine myself to the description of a phenomenon
which shews strikingly the beautiful order and regula-
rity with which nature disposes the fabric of some of her
minutest visible works.
The object I speak of is a kind of minute crystalliza-
tion which may be obtained in peculiar circumstances,
and I doubt not in many different ways ; but the manner
in which it has presented itself to my observation is as
follows : —
A crystal of borax is placed in a drop of phosphoric
• From Phil. Trans. Part I. for IE37.
214
APPENDIX.
acid, somewhat diluted, upon a plate of glass, and then
moderately heated until the crystal dissolves in the acid.
It is then set aside to crystallize. It is well to prepare
a number of these plates at once, varying the relative
proportion of the acid and salt, in order that the desired
kind of crystallization may be found in one or other of
them; for there is a considerable variety in the crystal-
line forms obtained by this method, some of which indeed
are very singular- But when that kind of crystallization
takes place which it is more particularly my intention to
speak of, the field of view of the microscope is seen
covered with minute circular spots, each of which is like
a tuft of silk radiating from a centre, and is composed
of a close assemblage of delicate acicular crystals forming
a star. But besides these, are seen interspersed among
them a number of circular transparent bodies, which are
evidently modifications of the former, being, in fact, tufts
or stars of acicular crystals, in such close assemblage as to
be in optical contact with each other, and to produce the
appearance of a single individual. Now let us suppose
a group of these circles to be under examination with the
polarizing microscope, and when the polarizers are
crossed we observe the following phenomenon : — The
field of view being dark, the little circles become lumi-
nous, and we see upon each of them a well defined and
dark cross, dividing the crystal into four equal parts.
All these crosses are placed similarly, and are parallel to
each other, and their direction remains unaltered when
the crystals arc turned round in their own plane by
ON THE OPTICAL PHENOMENA OF CRYSTALS. 215
revolving the plate of glass upon which they stand. This
beautiful appearance can be seen with a moderate mag-
nifying power. I measured the diameter of some of the
larger crystals, which I found to be from 1 -300th to
1 -600th of an inch. But there are many much smaller,
and indeed they may be seen decreasing in size, until
nothing remains visible of their structure but the four
luminous quadrants, appearing like four minute dots of
coloured light placed close together.
I proceeded to examine the circles with a high magni-
fying power, and under favourable circumstances of illu-
mination, and I observed in them a very admirable
structure.
Each circle has upon it one or more coloured rings
arranged concentrically, but the number as well as the
colour of these rings is different in different individuals.
The innermost ring is deeply coloured or black, and
incloses a central space of white light, which is traversed
by the arms of the cross intersecting in the centre. This
part of the cross, which stands within the innermost ring,
is beautifully well defined, and perfectly black. The
general appearance resembles the figure 98, in Brewster's
Optics, which is a representation of the rings seen in
uniaxal crystals. It especially resembles it in the circum-
stance above mentioned, viz. the more defined outline
of the part of the cross which is within the innermost
ring.
We have hitherto supposed the polarizers to be crossed;
but if we place them in a parallel position we shall sec
216 APPENDIX.
a phenomenon complementary to the above. The circle
now presents four patches of coloured light, one in each
quadrant ; and we generally see near the centre four
black or obscure spots, which correspond to the arms of
the cross in the other position.
Such is an outline of the microscopic appearances
presented by these little crystals, which are probably the
minutest bodies in which so complicated an optical struc-
ture has hitherto been witnessed. I find that the smaller
circles are, the more perfect is their form, and the
brighter their colours.
These crystals, as 1 have already observed, probably
consist of spicula diverging from a point, but which are
in the closest possible contact, and in a state of complete
mechanical cohesion. It seems to follow as a conse-
quence from such a structure, that their density must
increase from their circumference towards their centre.
Now it is worthy of remark, that Sir David Brewster has
discovered very similar phenomena by polarized light in
the crystalline lenses of certain fishes, which are known
by direct experiment to increase in density towards the
centre. Indeed the figure which he has given of the
lens of the codfish in the Philosophical Transactions for
1816 (Plate XII. fig. 1,) is so like the appearance of one
of the crystals which I have described, that it might be
supposed to have been intended for a representation of it.
Having pointed out this resemblance, I may also men-
tion another class of facts to which I think those I have
described possess a considerable analogy, I mean the
ON THE OPTICAL PHENOMENA OF CRYSTALS. 217
optical figures which Brewster lias discovered in spheres
of glass whose density was rendered variable by heating
them.
He says* that " if we take a cold sphere of glass and
immerse it in a trough of hot oil, placed in a polarizing
apparatus, we shall observe a black cross with four sectors
of polarized light. If the sphere is turned round, it will
exhibit in every position the very same figure. If we
now suppose the trough to be filled with such spheres,
they will exhibit the same phenomena in whatever direc-
tion the polarized light is transmitted through them, and
even if they were in a state of motion. A fluid com-
posed of such spherical particles would exhibit the same
polarizing structure in every possible direction, and even
if it were in a rapid state of gyration. If the particles
possessed the structure that produces circular polariza-
tion, the fluid would develop the phenomena exhibited
by oil of turpentine, &c."
And again-]- , " The structure of the particles of a cir-
cularly polarizing fluid must be exactly the same along
every one of its diameters ; that is, the structure must
be symmetrical round the centre of the particle, or
analogous to that which takes place in common polariza-
tion when a sphere of glass has its density regularly
increasing or regularly diminishing towards its centre."
I have quoted these remarkable passages at length,
because it appears to me that what is there advanced
* Library of Useful Knowledge, ait " Totalization oi Light," p. 51.
t Ibid. p. 15.
218 APPENDIX.
merely as a hypothesis, acquires a considerable degree of
probability from the facts which I have stated, since I
have succeeded in rendering actually visible circular
particles of excessive minuteness, in each of which
the microscope detects the very structure imagined by
Brewster, viz. the black cross and four sectors of light.
So that it appears not improbable that the circular
polarizing properties of fluids may be owing to the
presence of multitudes of particles similar to these, which
they hold in solution.
219
No. 2.
Further Observations on the Optical Phenomena of Crystals.
By H. F. TALBOT, Esq. F.R.S.*
Sect. I. — In my former paper on this subject I have
described the remarkable circular mode of crystallization
which sometimes occurs when borax crystallizes from a
solution in phosphoric acid.
I have stated that when examined by the polarizing
microscope, a black cross and four sectors of light are
seen upon each crystal j and upon that kind which is
most easily and frequently obtained, there are seen in
addition one or more rings of vivid colour. Some
deviations, however, from this usual form occur occa-
sionally ; one of which, being extremely beautiful as a
microscopic object, deserves a separate mention. This
variety of crystalline circles differs from the one first
described in the following particulars.
1. The circles are much larger, attaining the diameter
of one-tenth of an inch ; whereas those first observed did
not exceed one-two-hundredth of an inch in diameter.
2. They are flat, whereas the former ones were convex,
and frequently, 1 believe, of a spherical form.
* From Phil. Trans. Part I. for 1837.
220 APPENDIX.
3. In consequence of which probably, they are seen to
exhibit no coloured rings, but only a cross.
4. The cross is brightly coloured, red, green, blue, &c.
upon a white ground (the polarizers being supposed to
be parallel to each other). This has a beautiful appear-
ance, especially when several circles seen at once have
crosses of different colours.
5. When the polarizers are placed at right angles, the
phenomenon complementary to the above is seen. For in-
stance, the circle which presented a red cross upon a white
ground now presents a black cross upon a green ground.
6. In an intermediate position of the polarizers, the
circle just mentioned presents a red cross alternating
with a green one, thus dividing the circle into eight
sectors of coloured light.
Other circles present other colours, but they all follow
the same analogy, and the crosses upon all the crystals
are in a parallel position.
7. These crystals last longer than the former ones.
1 have found some of these retain their structure for two
months ; the former kind seldom last in perfection more
than a day.
8. It sometimes happens that their circumference is
imperfect, and presents a notched or jagged outline.
These have a very beautiful appearance, and have been
almost universally compared by those who have looked
at them to highly-coloured flowers with four petals ; the
cross upon them being so dark as to have the appearance
of being a division between the petals.
ON THE OPTICAL PHENOMENA OF CRYSTALS. 221
All the circles, when viewed by common light, appear
transparent, white, and very uniform. If they are com-
posed of acicnlar crystals diverging from a point, these
latter must be exceedingly slender and numerous, and in
perfect optical contact, since a high magnifying power
does not render them separately visible.
Sect. 2. — With respect to the chemical nature of
these crystals, it appears to me evident that they consist
of boracic acid. They are obtained by dissolving borax
in phosphoric acid ; and it may be inferred that this
latter substance unites with the alkali, and isolates the
boracic acid. In order to see if this supposition were
correct, I dissolved boracic acid in alcohol, and I found
that a drop of this solution evaporated on a plate of glass
frequently yielded an abundant crop of the crystalline
spherules. But these are generally exceedingly small,
requiring a high power to display in them the cross and
four sectors of light, and they speedily grow opaque ; for
which reason they are not so well suited for observation
as those prepared by the former method. They establish
the fact, however, that this mode of crystallizing is a
property of the boracic acid. It is highly improbable
that it should be peculiar to that substance, but I have
not yet met with it in any other.
Sect. 3. Explanation of some of the Optical appearances.
— 1. When any doubly refracting crystal is examined
with the polarizing microscope, (the polarizers being
222 APPENDIX.
transverse to each other, and the field of view conse-
quently dark,) if it be turned round in one plane, it is
seen to grow four times luminous and four times dark in
the course of one revolution. This I have found to be
universally the case with all the substances which I have
tried, and it also is in accordance with theory.
2. In the case of an acicular crystal one of the optical
axes always coincided with the axis of figure, or length
of the crystal ; so that if a crystal of this sort appears
unilluminated, all the others that are either parallel to it
or perpendicular to it are likewise dark.
3. It results from the above, that a circle composed of
acicular crystals diverging from a point must present the
appearance of a black cross, and that the crosses on all
the circles will be parallel.
4. With respect to the rings of colour, they are a con-
sequence of the variable thickness of the crystalline circle
at different distances from its centre. Their being visible,
and indeed very conspicuous, upon a body of such small
diameter, arises from the very energetic action of boracic
acid upon polarized light.
Sect. 4. I have remarked that the circular crystalli-
zation of boracic acid is frequently entirely superseded
by other modes of crystalline formation ; which circum-
stance appears to be chiefly owing to the presence or
absence of combined water. Some of these variations
deserve to be particularly specified.
1. Instead of circles there often occurs a formation
ON THE OPTICAL PHENOMENA OF CRYSTALS. 223
of crystals resembling two opposite sectors of a circle
combined. This form may be traced in different crys-
tals, from its commencement when the angle of the
sector is small, through all degrees of increase, until at
length the opposite sectors unite and form a complete
circle.
2. The crystals are frequently of a very irregular elon-
gated shape, which does not approximate either to a
prismatic or a cylindrical form. This stem, as it may be
termed, subdivides itself at both extremities into an
immense multitude of diverging fibres, giving it the ap-
pearance of a bundle of elastic filaments firmly held to-
gether in the central part, but with its extremities left at
liberty to diverge*.
3. Another variety resembles in the same way irregu-
lar stems or branches, which, however, instead of being
subdivided, are abruptly truncated at both extremities
perpendicularly to the general line of their direction.
4. Sometimes, on the contrary, the ramification is
much more developed, and then resembles two plumes
united by a common stem.
5. Crystals of regular geometric form. These appear
to require the presence of combined water.
Whichever of these formations occurs, it is for the
* This appearance is not very uncommon in the crystallization of other
substances, though I believe it has not yet been described. The divergence
of the filaments suggests the idea of electrical repulsion as being at least its
primary cause.
224 APPENDIX.
most part seen in all the crystals at once, to the exclusion
of any of the other forms.
Sect. 5. These crystals generally undergo a sponta-
neous change in the course of one or two days after they
have been formed. Those (No. 4) resembling plumes
usually break up and resolve themselves into small
rhombs and other geometric forms. The elongated
crystals (Nos. 2, 3) undergo a remarkable change. They
become traversed with innumerable fissures transverse
to their length, and thus break up into thin plates, which
either cohere loosely or separate entirely.
Sect. 6. All these forms are very pleasing objects for the
polarizing microscope. This arises from the very high de-
polarizing power of boracic acid, which enables its thinnest
plates to exhibit colours of great variety and brilliancy,
and causes even its dust or smallest particles to appear
luminous. The more energetically any substance acts
upon polarized light, the closer and more crowded are
the band and lines of colour which appear upon its
crystals. These isochromatic lines, of which there are
frequently many alternations, denote lines of equal thick-
ness in the crystal. In the case of boracic acid, when
anhydrous or nearly so, these lines are more crowded
than in any other crystal that I have yet examined, inso-
much that to exhibit them distinctly is as fine a test of the
performance of a microscope as to resolve the more diffi-
OPTICAL PHENOMENA OF CRYSTALS. 225
cult lines on the scales of a butterfly's wing, or any other
of the known test-objects. And in many cases the
microscope only indicates the existence of a still more
delicate structure, which, at least in its present state, it
has not power distinctly to exhibit.
Sect. /• On Analytic Crystals. — I now come to de-
scribe a property of crystals which I met with while em-
ployed in pursuing the above investigation. This is, the
power which certain crystals have of analyzing polarized
light in a manner analogous to the tourmaline ; for
which reason I shall propose for them the name of
Analytic Crystals.
If I am not mistaken, this property has been hitherto
confined to the tourmaline and a few other natural
minerals: and it has not been known that their effects
could be imitated, much less surpassed, by crystals arti-
ficially made. I trust, therefore, that it will be of some
interest to describe a method of procuring such crystals.
In the following experiments it will be understood
that the analyzing plate of the microscope (or the pola-
rizer next the eye) is removed.
1. A good example of this kind of crystal is obtained
by dissolving the sulphate of chromium and potash in tar-
taric acid by the aid of heat. A drop of this solution
placed on a plate of glass soon yields by evaporation
filmy crystals, which very frequently have the charac-
teristic property of tourmaline : that is to say, that if
Q
226 APPENDIX.
polarized light is transmitted through them, in one posi-
tion they suffer it to pass freely, but if they are turned
round 90 degrees, they arrest and absorb it entirely.
When the experiment has been successfully conducted,
the crystals will not in this position allow the smallest
portion of light to pass.
If now we consider the extreme thinness of these crys-
talline films, it will appear how energetic must be their
action upon light ; since, although white and transparent,
they are able to produce an absorption equalling that of
the best tourmalines, notwithstanding that the effect of
the latter is aided by their natural dark colour.
But if these crystals are analogous to the tourmaline,
they must have the power which that substance has of
analyzing the light that has been transmitted through
other crystals.
Accordingly, if we place in the path of the polarized
ray a plate of sulphate of lime of a proper thickness, the
crystal which before absorbed the light and appeared
black, becomes splendidly coloured with that colour
which the sulphate of lime produces, and which a tourma-
line would shew if it were employed as an analyzing plate.
On reversing the polarization of the ray (or turning
round the crystal), the complementary tint appears. The
same results occur if the crystal is employed in the first
place to polarize the light, and tourmaline or calcareous
spar is used to analyze it, so that the analogy or rather
identity of effect with the tourmaline is complete.
OPTICAL PHENOMKNA OF CRYSTALS. 227
1 will now mention some other crystals which possess
the analyzing property, but not in such a high degree.
2. Boracic acid. — If dissolved in boiling water, it yields
in cooling irregular crystals which have considerable
analytic power. A crystal which in one position is so
translucent as to be hardly distinguishable from the
water in which it floats, is in the transverse position
very strongly defined. It does not become dark all over,
but only in its outline.
If now we employ it to analyze the tints of sulphate of
lime, its outline becomes beautifully coloured. Nothing
can exceed the delicacy of colouring which a number of
these crystals exhibit when viewed together ; those which
lie in one direction appearing, for instance, green; those
in a transverse direction, red. The appearance is very
unlike any other optical phenomenon that I know of, in
consequence of two colours being seen in strong contrast,
and without any intermediate tints ; and also from the out-
line only of the objects being coloured, while their interior
remains without colour. It is only when the crystals
have a fibrous or striated structure that the tint extends
over all their surface.
The boracic acid has the same analytic property, and
precisely the same appearance, when it crystallizes from
a solution of borax in phosphoric acid. The plumose
crystals of it (No. 4, supra) are very delicately coloured
with the two opposite tints.
I obtained a very beautiful result by placing a drop of
phosphoric acid upon a group of circular crystals. This
228 APPENDIX.
caused a fresh deposition of boracic acid upon them as
nuclei, which assumed the form of very delicate cilia,
spreading in all directions as from a centre. These
fringed circles shewed the analytic property in an admi-
rable manner, exhibiting four quadrants coloured alter-
nately with complementary colours of great vivacity.
3. Another instance which is worthy of mention is the
oxalate of potash and chromium, a salt whose optical pro-
perties have been investigated by Sir David Brewster*.
If some gum arabic is added to a solution of this salt, and
a drop of it put between two plates of glass, it abandons
its usual mode of crystallization for another, which re-
sembles a microscopic vegetation composed of minute
prisms growing one out of another, and variously ar-
ranged in sprigs and branchlets ; while in other places
it assumes an undulating capillary form, much resem-
bling in miniature the tufts or locks of a species of
Conferva which is seen growing in pools of water or in
the sea. Now these objects are possessed of a high
analytic power, insomuch that, when a plate of sulphate
of lime is placed beneath them, they assume a colour of
great intensity and splendour, which is changed for the
complementary tint when the polarization of the incident
ray is reversed.
4. Nitre. — If nitre and gum arabic are dissolved to-
gether in hot water, a drop of the solution put on a glass
plate yields very good analytic crystals. These have a
* Philosophical Transactions for 1835, p. 91.
OPTICAL PHENOMENA OF CRYSTALS. 229
branched or plumose appearance, and assume beautiful
colours in polarized light when a plate of sulphate of
lime is placed beneath them. The microscope shews the
colour to reside principally in the outline, but to the
naked eye the whole film appears coloured. As these
films may be obtained of large size, the phenomenon can
be well seen by the unassisted eye.
A very interesting experiment, and one which throws
much light upon the cause of these appearances, is to
transmit a beam of polarized light very obliquely through
a small prism of nitre immersed in gum, and viewed
with the microscope. Its outline then generally exhibits
two colours instead of one ; for, while the edge of the
prism which is on that side from whence the ray of light
comes, is, for instance, of a red colour, the opposite ci\ge
Mill appear green. Reverse the polarization of the light,
and these colours are exchanged one for the other. This
observation enables us to explain the origin of the pheno-
menon in a satisfactory manner, and to shew why it only
occurs in crystals possessing strong double refraction,
like nitre, in which the refractive indices of the two rays
are materially different.
When a ray of common light is incident upon such a
crystal, and therefore divides itself into two rays oppo-
sitely polarized, both rays are transmitted through the
central parts of the crystal, which are bounded by parallel
planes, or by planes approaching to parallelism. But
when the bounding planes of the crystal are much in-
2?0 APPENDIX.
dined to each other, and therefore refract the light in
the manner of a prism, the refractive indices of the rays
may differ so much, that while one of them passes freely
through such a prism, the other cannot pass at all, but
suffers total internal reflexion, and is thereby dispersed ;
just as if the prism had a larger refracting angle with
respect to that ray than to the other. Therefore if two
oppositely polarized rays are presented successively to
such a crystal, as in our experiment, one of them will be
transmitted, and the other not. That this is the true
explanation appears from this, that when the oblique
planes are well formed and clearly defined by the micro-
scope, the colour also is accurately limited by the same
boundary : so that while this part analyzes the tints of
a plate of sulphate of lime, the rest of the crystal is
inactive.
It may be inferred by analogy, that the same cause
produces the analyzing power of striated or fibrous sur-
faces, and of those in which the striae are too minute to
be discernible (as in No. 1, supra, page 225) : for it is not
the property of all crystals with striated surfaces to have
the analytic power, but only of such as are doubly
refractive in a high degree,
I have said that the capillary crystals (No. 3) possess
the analytic property, although their diameter is often
evanescent even with a microscope. An important infer-
ence may be drawn from this, viz. that a ray of light imme-
diately on entering one of these crystals, subdivides itself
OPTICAL PHENOMENA OF CRYSTALS. 231
into two rays of different refractive indices, or at least
that the thickness of crystal which is requisite to pro-
duce this effect is insensible to observation.
When nitre is made to crystallize in gum, it often
shoots into prismatic crystals, which are very interesting1
objects, the more so, that they are of a permanent nature,
and not liable to spontaneous change. When examined
by polarized light, these prisms, in one position of their
axis, frequently disappear completely. This arises from
the refractive power of the gum being equal to that of
one of the two rays in the crystal. Reverse the polari-
zation of the ray, and the crystal appears, as it were, to
start into existence, acquiring great strength and black-
ness of outline, and, not unfrequently, entire opacity.
Again, when the sulphate of lime is interposed, this
opacity disappears, and the crystal becomes brightly
coloured. Since it is probable that many better methods
may be found of obtaining this kind of crystal than have
hitherto presented themselves, I have hopes that it will
be possible to obtain large and permanent artificial
crystals, which may possess the advantages of the tour-
maline without the inconvenience resulting from its dark
colour.
232
No. 3.
E X 0 11 1) I U M *.
By C. R. GORING, M.U.
The discovery of a set of objects for ascertaining the
defining and penetrating powers of microscopes, has
founded a new era in the history of those instruments.
The thick aplanatic object-glass for diverging rays, and
the Amician reflecting microscope, have in consequence
been perfected. The substitution of diamond and sap-
phire lenses, for those made of glass, in the single micro-
scope, with the ingenious apparatus for illumination
contrived by Dr. Wollaston, may also in some measure
be attributed to the same source. It may surely be
affirmed that no improvements at all commensurate to
these in magnitude and importance are likely to be made
hereafter. Microscopes are now placed completely on
a level with telescopes, and, like them, must remain
stationary in their construction.
In the present work I have endeavoured to establish
the mechanical part of the construction of microscopes,
* From First Edition, with corrections. By C. R. G.
EXORDIUM. 233
that is to say, their mountings, carriages, and apparatus,
&c. on true and philosophical principles, and I Hatter my-
self not totally without success, most of the better class of
instruments, which have been made of late years, being
more or less constructed according to the plans I have
suggested. This, however, is a subject on which no man
must pretend to dogmatize or dictate, for such is the spirit
of contradiction, and of renitency against conviction, in
mankind, that they will make it a point of honour to go
the wrong way if you urge them too forcibly on in the
right one, just to shew that they will have their own way,
and are determined to think and act for themselves.
Though it may savour somewhat of egotism, I cannot
refrain from stating some of the difficulties which I
experienced in making the drawings of the living objects,
though I know very well that people of first-rate talent
explode difficulties, and will hardly allow of their exist-
ence, except with bunglers and half-taught amateurs.
I wish I had been one of those favoured individuals with
whom the most arduous achievements of all sorts
" are no more difficile.
Than for a blackbird to whistle."
Hudibras.
If any portrait painter had to execute a likeness of
some person afflicted with chorea, who could not be
prevailed upon to be quiet for more (ban ball a mi-
nute together, who was perpetually jigging about the
apartment, and exhibiting his tail instead of his head,
234 APPENDIX.
&c. &c, I think he would be compelled to admit
that he had undertaken a task which would at least
require time and patience for its completion ; but if,
in addition, the said person was to be removed to a
distance, so that the artist could only see him with a
powerful telescope, and had to follow his motions as
well as he could, and be content to catch a glimpse of him
crossing his field of view now and then, according to the
humour and good pleasure of the said individual, I
think the worthy limner would begin to think that after
all there was some difficulty to contend with.
Now this case I conceive to be an exact parallel to
that of drawing living objects with a microscope.
Their incorrigible restlessness so baulks and baffles the
artist, that he is frequently compelled to lay down his
pencil to regain his lost temper, and fresh courage to
proceed : in many cases his best resource is to study the
object till he has got all its features by heart — then to set
them down on paper — study again, and gradually cor-
rect them : by the time he has made half a dozen rough
sketches he will get pretty near the truth : he may then
commence a regular drawing. I can safely say that I
have drawn many of my objects five or six times over
before I could arrive at my portraiture. I have heard a
great deal about shutting one's eyes after having made an
observation, and drawing from the impression left on the
retina. This, I suspect, is better in theory than in prac-
tice, and it is evident that, unless the object is stationary,
EXORDIUM. 235
the last impression must be so confounded with the
preceding ones that no distinct image can be left.
But it will probably be asked, why I did not kill my
object before J drew it, instead of giving myself all this
unnecessary trouble ? I answer, that I never could make
a drawing to my mind from a dead aquatic larva or
insect. Such is the extreme delicacy of their organs,
and so rapid their decomposition in water, that long
before a drawing can be executed, the main and capital
parts of the internal, and even external structure, in
most subjects, will become confused and unintelligible.
If they are removed out of the water, a still greater
change is effected by their drying : their colours vanish,
and their whole appearance is totally changed ; to say
nothing of the fact, that a dead aquatic insect so loses
the peculiar distinctive character derived from its
favourite attitude and position, that though the com-
ponent parts might, in some instances, be correctly given,
the tout ensemble would be scarcely recognized. Some
of the proportions — length of the body and legs, &c. — may,
however, be measured from the dead subject ; and this
help I have always had recourse to when I could spare a
specimen for destruction. All attempts to preserve these
creatures in spirits, turpentine, &c. are useless, from the
excessive corrugation these liquids produce. I also made
various attempts to confine them in a narrow compass
so as to prevent much latitude of motion ; but was com-
pelled to desist from the project, finding that they got
236 APPENDIX.
into constrained and unnatural positions, and injured
themselves by struggling-.
At the period the drawing's were made, it is proper for
me to observe, that the happy method of preserving
aquatic insects in Canada balsam or varnish was not
discovered; still, however, a live subject is far superior
to a dead one, under any circumstances whatever ; which
proposition I consider so self-evident that I shall not
set about proving it.
] suspect that other individuals have met with the same
obstacles as myself in making drawings of living micro-
scopic objects ; for I think it may be affirmed, without any
illiberality, that, with very few exceptions, those of my
predecessors are proportionally more rude and incorrect
than those of any other subjects of natural history what-
ever; their various lineaments and features being fre-
quently false, and exaggerated to a degree amounting to
caricature ; nevertheless, they have been handed down
from one bookmaker to another, ever since the days of
Swammerdam, as if they needed no improvement what-
ever. I have made my drawings at that period of the
growth of the larva or crysalis in which I thought it
made the best and most interesting object, and that they vary
greatly in their appearance, according to the degree
of maturity to which they have arrived. There are also
many varieties, very closely resembling each other, which
it is not very easy to particularize ; but I am quite con-
fident;, that when the genuine object is procured, in the
EXOKDfUM. 237
state in which I drew it, the correctness of my execution
will be recognised.
The specimens which I have selected are those which
experience has shewn to excite the strongest emotions of
pleasure and satisfaction in the great mass of observers
of all ranks; whom I have always found to be most
delighted by comparatively large living objects, seen with
medium powers. In fact, they seem to afford the same
sort of gratification with a menagerie of living wild
beasts on the large scale ; and most certainly many of
them wonderfully emulate the ferocity, voracity, cunning,
and cruelty of the mammalia. They prey on each other,
and fight with a degree of determined obstinacy not
inferior to that of any beings whatever. They have like-
wise a thousand diverting pranks and humours, quite
peculiar to themselves. In addition to these amiable and
amusing qualities, they possess such a high degree of
transparency, that their unique and beautiful internal
machinery is as clearly perceptible as if they were made
of glass; so that, without any dissection, we can unravel
all the mysterious workings of their nature; such as the
circulation of the blood, the pulsations of the heart, the
peristaltic motion of the intestines, and the play of every
muscular fibre. This property of transparency is not
possessed by any other living beings with which I am
acquainted, except the animalcula infusoria. I may
observe, that no perfect insects present so many facilities
for adaptation to the microscope, or can be so easily
preserved and managed ; so that the larvae, &c, appear
238 APPENDIX.
to me peculiarly and exclusively devoted to the conside-
ration of microscopists.
Their natural history will be given by Mr. P., with
every particular likely to interest the reader concerning
their peculiar habits and instincts : such as their mode of
locomotion, and of taking their prey ; the food which
they most affect; their relative dispositions towards each
other, and other beings with whom they associate; with
full directions how, when, and where to procure them ;
and how they may be preserved in health and vigour for
observation, &c. &c.
I do not feel myself called upon to state more con-
cerning the nature and object of this work ; and 1 humbly
hope that truth and justice to myself and partner, and
our joint publication, does not require me to have said
less.
I shall conclude this introduction by a vindication of
microscopic science and its votaries, from the aspersions
which have been cast upon them by the inconsiderate ;
many of whom have been pleased to assert, that micro-
scopes have, of late, received a degree of patronage from
the most illustrious and distinguished savans, to which
they are not legitimately entitled. Were they applicable
to no other purposes than the dissection of blackguard
vermin, the observation of stinking ditch-water, or the
amorous passions of ants and worms, I should, perhaps,
for argument's sake, admit that they were but the tools
of a puny, pitiful pedant, whose passions and amusements
were of a trifling, if not of a degrading complexion : but
EXORDIUM. 239
I would ask whether, in the hands of men like Bauer,
they are not applied to the development of the most
curious, important, and interesting details of anatomy
and physiology, which, without their assistance, could
never have been known ? and whether the finest and
most delicate parts of the structure of animals, in their
extreme penetralia, are not rendered equally intelligible
with the coarsest and most evident parts of their fabric,
by means of these instruments?
None are apt to treat microscopists with more contempt
than some astronomers, and even mere star-gazers.
I shall always possess the most profound veneration
for astronomy, as the most sublime of all the sciences ;
but star-gazing is a distinct department, though fre-
cpiently confounded with it ; and is, in my opinion, little
better than downright microsophizing. To the telescope
certainly belongs the inspection of the great and sublime
works of the creation ; to the microscope belongs the
petites and beautiful ones : if the former shews us the
world above, the latter exhibits the world beneath us.
I must here positively chant the vast superiority of a
microscope, as a hobby-horse, over a telescope, at least
when the latter is used merely as a star-yaziny in&trut
ment. Let us suppose you have, at a great expense,
procured a very fine telescope. How many hours in
the year will you be able to use it ? Not above one
hundred, says Sir W. Herschel, even if you lose not
one in other avocations. How many colds and quinzies
are you to get by exposure to the night air, when you
240 APPENDIX.
might be much better employed in your warm bed ?
How many disappointments are you to endure from
finding the wind suddenly shift into the wrong quarter,
after you had counted on a good night's sport ? How
many scoldings and curtain lectures from your wife ?
After all, when you have seen all the double stars, clus-
ters, nebulae, within reach of your instrument, together
with the planets, mountains in the moon, and spots on
the sun, &c. together with any curious terrestrial objects
about your habitation, and exhibited the same to your
friends, what remains but to dispatch your charmer up
to the garret, as of no further use ? You may, certainly,
on high festivals, transport it down again, in order to
convince people what a prodigiously scientific personage
you are, even to be able to possess such an instrument,
and to know the right end of it from the wrong one.
A microscope, on the other hand, is available at all
times and seasons. There is no end to the number of
objects it may investigate. In the solitude of the most
dismal prison, you would only need a lamp, a microscope,
and some vegetable infusions, to furnish you with an
inexhaustible fund of amusement, totally independent of
other external objects. When employed in researches
on animal and vegetable physiology, where are your in-
vestigations to terminate ? Your life will not suffice
to study sufficiently the wonders of the minutiae of
natural history.
The supreme Author of Nature has been pleased to
bestow so exquisite a degree of finishing upon
EXORDIUM. 241
many of his works, that they can he only appreciated
hy man with the assistance of the microscope. Surely
he who is hut a work of God may he allowed to admire the
works of his Creator, without incurring- derision or ridi-
cule, even though they are minutiae. Trifles are said to
take only with frivolous minds ; hut minutice are not ne-
cessarily trifles, as it will be easy to prove. It is not
only, in my own opinion, unscientific, but even swinish
and ridiculous, to contemn any thing merely on account
of its minuteness. To say nothing of the hackneyed ar-
gument, that greatness and littleness exist only by com-
parison, I will ask, if the Automaton Chess-player had
been made on a scale of l-20th of an inch to a foot, or
even much less, it would, in consequence, become despi-
cable as a work of art ?
Suppose some individual, greatly distinguished by his
talents in shipbuilding, in making astronomical instru-
ments, or steam engines, &c, was also to evince a passion
for making minute automata and watch-work, such as
tarantula spiders, minute singing-birds, musical seals, or
even such curiosities as a coach drawn by fleas, &c.
would it shew good breeding, or good taste, to despise or
ridicule his minute labours, while we admired his
grander and more imposing works ?
Now it does appear to me, that the Supreme Being
docs, in some sense, resemble such an individual ; for
his power loves to display itself in every way in which it can
be displayed, whether upon the minute or grand scale, in the
creation of animalcules, as well as of fixed stars and I
it
242 APPENDIX.
cannot help thinking- myself, that those who spurn and
scoff at the minute ivorks of God, be they what they may,
while they affect an admiration of his great wonders, are
guilty of a species of impiety, and must be either liars, or
hypocrites, or fools.
Men are perpetually wondering what can be the use of
bugs, and fleas, and wasps, and such kind of vermin, and
speak of them as absolute blots in the escutcheon of the
Almighty. The use of these little insects is surely to
teach man a perpetual lesson of humility. He is extremely
apt to fancy himself the only being of real importance in
this planet, and that every thing in it has been made for
his exclusive use and accommodation : whereas a very
little consideration must teach him that the said fleas, and
bugs, and wasps, &c. are intended to enjoy themselves in
their own ivay just as he does ; that is to say, without
greatly considering the convenience, comforts, or happi-
ness of other beings, I consider it as certain that bugs
were intended to prey upon man, as that man and the
other prredaceous mammalia were intended to destroy
the weaker animals. If a bug (I beg pardon — a cimex
lectularius) could reason, it would probably suppose that
man was of no other use in the creation than to prepare
its habitation and supply its food ; and would think that
no better evidence need be adduced to prove the immense
importance of a bug than that such bountiful provision
had been made for it, &c.
If mere utility is to be made the standard of excellence,
what a large part of that of most of the sciences consists
EXORDIUM. 243
in their effect as counterpoises to superstition and barbarism !
and in this point microscopic science surely 1ms its voice
among the rest. All men are apt to despise their neigh-
bours' pursuits, and to dignify their own as the only ones
of real importance and value : but while the use of the
microscope is sanctioned by the examples of Pond, of
Amici, of Wollaston, of Herschel, and of Brewster,
who disdain not to relax from their severer studies in
such pursuits, he must be very hardy and fastidious in-
deed who dares to deride and condemn them.
Great disgrace has been brought on microscopic
science by the manner in which it has been perverted to
the support of preconceived opinions and hypothetical
views, as well as to a spirit of M'onder-making. I hope
that a new and golden age of observation will now
commence.
C. R.G.
March 1837.
241
No. 4.
Observations on Sivammer dam's method of Dissecting and
Preparing Objects for the Microscope*.
Referred to at page 121.
In the preparation of objects, no man was more success-
ful or more indefatigable than Swammerdam : in minutely
anatomizing-, in patient investigation, and in curiously
exhibiting the minute wonders of creation, he stands
unrivalled, far exceeding all those that preceded, as
well as those that succeeded him. Deeply impressed
and warmly animated by the amazing scenes that he
continually discovered, his zeal in pursuit of truth was
not to be ahated by disappointment or alarmed by diffi-
culty, and he was never contented till he had attained a
rational and clear idea of the organization of the object
whose structure he wished to explore.
We have only to regret that we are ignorant of the
methods he employed. To discover these, the great
Boerhaave examined with a scrupulous attention all the
letters and manuscripts of Swammerdam, and has com-
municated the result of his researches, which, though but
* Adams's Essays on the Microscope, p. 134, from the Life of Swammer-
dam, by Boerhaave, ed. 1758.
OBSERVATIONS ON DISSECTING, ET( . 215
small, may enable us to form some idea of this great
labourer in the field of science.
His chief art seems to have been in constructing very
-fine scissars, and giving them an extreme sharpness ;
these he made use of to cut very minute objects, because
they dissected them equally ; whereas knives and lancets,
let them be ever so fine and sharp, are apt to disorder
delicate substances, as in going through them they gene-
rally draw after and displace some of the filaments. His
knives, lancets, and styles, were so very fine that he
could not see to sharpen them without the assistance of
a magnifying glass ; but with them he could dissect the
intestines of bees with the same accuracy and distinctness
that the most celebrated anatomist does those of large
animals. He was particularly dexterous in the manage-
ment of small glass tubes, which were no thicker than a
bristle, and drawn to a very fine point at one end, but
thicker at the other. These he made use of to show and
blow up the smallest vessels discoverable by the micro-
scope— to trace, distinguish, and separate their courses
and communications, or to inject them with very subtile
liquors.
He used to suffocate the insects in spirits of wine, in
water, or spirit of turpentine, and likewise preserved
them some time in these liquids; by which means he
kept the parts from decomposition, and consequently
eollapsing and mixing together ; and added to them such
strength and firmness as rendered the dissections more
easy and agreeable. When he had divided transversely
246 APPENDIX.
with his fine scissars the little creature he intended to
examine, and carefully noted every thing that appeared
without further dissection, he then proceeded to extract the
viscera in a very cautious and leisurely manner, with other
instruments of great fineness ; first taking care to wash
away and separate, with very fine pencils, the fat with
which insects are very plentifully supplied, and which
always prejudices the internal parts hcfore it can be
extracted. This operation is best performed while the
insect is in the pupa or chrysalis state.
Sometimes he put into the water the delicate viscera
of the insects he had suffocated ; and then shaking
them gently, he procured himself an opportunity of
examining them, especially the air-vessels or trachaea,
which by this means he could separate, from all the
other parts, whole and entire, to the great admiration of
all those who beheld them : as these vessels are not to be
distinctly seen in any other manner, or, indeed, seen at
all without damaging them, he often made use of water,
injected by a syringe, to cleanse thoroughly the internal
parts of his insects ; then blew them up with air, and
dried them, by which means he rendered them durable,
and fit for examination at a proper opportunity. Some-
times he has examined with the greatest success, and
made the most important discoveries in insects that he
had preserved in balsam*, and kept for years in that
* It is probable that the beautiful plan now adopted of mounting and
preserving insects in Canada balsam is the same as that here alluded to ;
notwithstanding it may be considered as a new discovery, because the
OBSERVATIONS ON DISSECTING, ETC. 21/
condition. Again, he has frequently made punctures in
other insects with a fine needle, and after squeezing out
all their moisture through the holes made in this manner,
he filled them with air, hy means of very slender glass
tubes; then dried them in the shade; and, last of all,
anointed them with oil of spike, in which a little rosin
had been dissolved, by which means they retained their
proper forms for a long time. He had a singular secret
whereby he could so preserve the nerves of insects that
they used to continue as limber and perspieuous as ever
they had been.
He used to make a small puncture or incision towards
the tail ; and after having gently and with great patience
squeezed out all their humours, and great part of their
viscera, he then injected them with wax, so as to give
and continue to them all the appearance of healthy,
vigorous living creatures. He discovered that the fat of
all insects was perfectly soluble in oil of turpentine:
thus he was enabled to shew the viscera plainly, only
after this operation he used to cleanse and wash them
well and often in water. He frequently spent whole
days in thus cleansing a single caterpillar of its fat, in
order to discover the true construction of this insect's
heart.
His singular sagacity in stripping off the skin of cater-
pillars that were on the point of spinning their cones,
account given by Swammerdam is not sufficiently explicit to point out the
mode of applying it.
2-18 APPENDIX.
deserves particular notice. This he effected by letting
them drop by their threads into scalding water, and
suddenly withdrawing them ; for by this means the
epidermis peeled off very easily ; and when this was
done he put them into distilled vinegar and spirit of
wine mixed together in equal proportions, which, by
giving a proper firmness to the parts, afforded an oppor-
tunity of separating them, with very little trouble, from
the exuviae, or skins, without any danger to the parts ;
so that by this contrivance the pupa could be shewn to
be wrapped up in the caterpillar, and the butterfly in the
pupa. Those who look into the works of Swammerdam
will be abundantly gratified, whether they consider his
immense labour and unremitting ardour in these pursuits,
or his wonderful devotion and piety. On one hand, his
genius urged him to examine the miracles of the great
Creator in his natural productions ; while on the other,
the love of that same All-perfect Being, rooted in his
mind, struggled hard to persuade him that God alone,
and not His creatures, was worthy of his researches,
love, and attention.
THE END.
Wilson and Son, Printers, 57, Skinner Street, London.
A LIST OF
NEW OPTICAL INSTRUMENTS,
CONSTRUCTED
By ANDREW PR1TCHARD, No. 162, Fleet-Street, London.
All the following instruments drawn and described in the Micrographia are marked
with the letter M., and the number following it refers to the page ; those described in the
Microscopic Cabinet have the letters.1)/. C.j and those given in the new edition of the
Microscopic Illustrations have 31. I.
£. s. d.
1. Pocket Microscope, with single magnifiers, (M. C. 243) 2 2 0
2. Vertical Microscope, with solid gun-metal bar, (M. I.) 5 5 0
3. ,, „ Achromatic, (M. I.) 7 7 0
4. ,, „ „ » (1 set best glasses) ... 10 10 0
5. Achromatic Microscope, with stand and round foot (M.I. ), ^lO. 10s. to 15 15 o
6- » „ » tripod,, (M.I.) ^12. 12s. to 18 18 0
7. Single „ „ „ „ (M.I.) ..10 10 0
8. Achromatic „ „ „ „ with candle holder,
condenser, dissecting rest, aquatic live-box, &c. in maho-
gany cabinet, with drawers 21 0 0
9- „ „ u „ „ ditto, with 2 sets
object-glasses, 1 best and 1 foreign, moveable stage, phial-
holder, 6cc. in cabinet 26 5 o
10. „ „ „ „ „ ditto, with from 3
to 6 sets best object-glasses — 3 Huygenean eye-pieces,
micrometer, drawing, and camera lucida eye-pieces — fine
adjustment; dissecting apparatus, &c. as described in
M.I. chapter vi ,,£35 to
11. Goring's Aplanatic Engiscopes, (M. I.) o£25 to
12. ,, Improved Amician Reflecting Engiscopes, (M.) ^18 to 50 0 0
13. „ Phial Microscopes, (M. I.) 5 5 0
14. Wollaston's Doublet Microscopes o£2. 12s. 6rf. to 10 10 0
15. Solar Microscopes 15 15 q
16. „ „ with achromatic glasses
17. „ „ with opaque apparatus
18. Lucernal Microscopes
19. Microscopes for measuring refractive powers
20. Single Dissecting Microscopes 7 7 0
21. Oxy-hydrogen Gas Microscopes 40 0 0
22. ,, .. » second size o£l0. 10s. to 25 0
23. „ „ Polariscopes
This apparatus exhibits on a screen the system of rings, colours of
thin plates of crystals, unanuealled glasses, prismatic spectrum, &c.
24. „ „ Apparatus for either of the above instruments, on
various constructions ^8. 8s. to 25 0
The construction of this apparatus is greatly simplified, and, independent
of its use for the microscope and polariscope, is admirably adapted for
shewing the combustion of metals and chemical experiments re-
quiring intense heat.
25. Improved Clock-lime Holders
26. Object-glasses, cylindrical, or Stanope
07. grooved sphere, or Coddiugton
28. „ concentric, or Brewster's ...
29. n Goring's double
;50. „ Herschel's aplanatic
0
£. s. d.
31. Object glasses, Achromatic, foreign (seconds) 1 10 0
32. „ „ >, (^st)
33. „ » English (best)
For the foci, apertures, and powers, given by achromatic object-glasses,
see M. I.
34. Spherule magnifiers, from l-30th to l-300th of an inch focus
35. Single, Doublet, and Triplet Glass Magnifiers, mounted
Focal Magnifying Power. Single Lenses. Doublets. Triplets,
lengths in „., j, j it . j V * d
parts of inch Linear. Superficial. £. «• d. £. s. d. t. s. a.
One inch 10 ... 100 times ... 0 4 6 ... 0 7 6 ... —
l-2d ... 20 ... 400 — ... — ••• — — ~
l-3d ... 30 ... 900 — ... — ... — - —
l-5th ... 50 ... 2500 — ... — ••• — — —
l-10th .. 100 .. 10000 — ... 0 9 0 ... 1 0 0 ... 1 10 0
l-20th ... 200 ... 40000 — ... 0 12 0 ... 1 10 0 ... —
l-30th ... 300 ... 90000 — ... 0 16 0 ... — ... —
l-40th ... 400 ... 160000 — ... — ••• — — —
l-50th ... 500 ... 250000 — ... — — — ••• —
l-60th ... 600 ... 360000 — .. — — — ••• ~
l-80th ... 800 ... 640000 — ... — ••• — ••• _
36. Single and Doublet Diamond, Sapphire, and Garnet Magnifiers
37* Pocket Magnifiers, in tortoise-shell frames, various
gg' ' 2 lenses, in neat frame .,
39" ,, and 1 Coddington
4q\ Coddington mounted, in silver
41. M Stanope
40' in pearl and silver ••••
„ 3 crystal lenses, in best flat mounting 2 2 0
44' fJ 2 crystal lenses, and 1 tourmaline ... 2 12 6
45' Tourmalines, mounted in silver and pearl, for the pocket ... 18*. to 1 10 0
46*. Telescopes, Achromatic, day and night, 1 foot, 2 feet, and 30-inch ...
47 )( Astronomical, 3£ feet and upwards ...
48* ■Reflecting, from 2 to 8 inches diameter
49'# " Stands, brass, for the table, various
50>' „ wood, improved garden •
gj t ,, equatorial \ •
52* Microscopic Gnoneometers, for measuring the angles of object-glasses
and specula, (M. C. 223)
53. Machines for making thin sections of woods
54. Knives for ditto • •'."'*','
55 Solid Pyramid Opera-glasses, mounted in silver
56 Prism Telescopes, for exhibiting Fraunhofer s lines
5/ Pocket Apparatus, for showing the interference of light
5s! Telescope and ditto „ „ » complete
59. ,, „ „ „ „ improved mounting
60. Heliostats, with clock-work
61. Gowland's Self-adjusting Artificial Horizons V^TT a m n
62. Polariscopes, with 5 to 8 crystals £%• f to 4 lu n
63 ?> Pritchard's improved slider ,^1. 8s. to 4 4 0
This Polariscope enables the possessor to examine sections of any
crystals that present themselves, and to augment their number at any
time.
64. Slides, containing three crystallized plates, for exhibiting the systems
of coloured rings by the above instrument, each slide ... 10s. 6d. to 1 1 0
65. Japanned Reflectors, for polarizing light • •• 0 4 6
66. Polarizing Prisms mounted to Microscopes for shewing coloured
tints, &c. in minute crystals, (M. I.) 30s. to 4 4 0
67 Stage, Double Object-glass/Tourmaline, &c. for shewing
unannealled glasses, selenite devices, system of rings,
structure of quartz, &c. by the Microscope, (M. I .) ...
£. s. d.
63. Moveable Stages, (M. I.) =£2. 10s. to
69. Fine Adjustments, (M. 218) 7<T»'T
70. Dissecting Instruments, in cases £Z.Zs.\o
71. „ Scissars (M. C. 244) 0 7 0
72. ,, Handles
73. ,, Needles •
74. Writing Diamonds, for marking names on slides
f5#' turned points.:
76. Microscopic Lamps, with shades
77. Condensers and Mirrors, various sizes
78. Cylindrical Glass Vessels, for holding aquatic insects and plants
79. Flattened ditto
80. „ Troughs, (M. 14)
81. Aquatic Live-Boxes, (M. I.)
82. ,, with thin glass covers
03 M and Micrometers
84. Micrometers on glass, mounted in ivory, l-50th to l-200th 0 3 <
1 -500th to 1 -5000th
86. >> on pearl slips
87. ,, fine screw, for the stage ...
88. ,, ,, eye-piece
89] ,, Drawing Eye-pieces, with improved adjustment, (M. I.)
90. Camera Lucida Eye-pieces, various
91. Rectangular Prisms Boots, (M. I -••••
9*. Phantasmagoria and Magic Lanthorns ••• *2. 2s. to
°3. Improved Astronomical Slides, for Magic Lanthorns, &c. (the motions
obtained by wheel-work)— Solar System, shewing the Motion of
all the Planets; Parallelism of Earth's Axis; Comet's Elliptic
Orbit ; Earth's Annual and Diurnal Motion, with the Moon's
periodical Revolution ; Phenomenon of the Tides illustrated ;
Apparent Retrograde Motion of Venus ; Rotundity of the Earth ;
Diurnal Motion of the Earth, the Rising and Setting of the Sun ;
Annular and Partial Eclipse ; Spots on the Sun— in sets or single
94 Slides, for ditto, of Costume, Buildings, Natural History, Comic
Subjects &c per dozen
95. Ditto, moveable •••■• per dozen
96. Sylphitrope figures, for revolving on a wet inclined plane ..each 0 j 6
97. Unannealled glasses, for shewing coloured tints by polarized light ...
98. Devices of Selenite, for ditto «"T« ™ \ n
99. Windows, Figures, &c ^1. 10s. to 20 0 0
100. Tourmalines, unmounted, each £s- t0 * 1U
101. Single Image Calc Prisms, £ to 2 inches long 7s. to
102. Double Image QuaTtz Prisms - '-"."'""
103. Crystallized Plates of Amethyst, Arragonite, Beryl, Borax, Sulphate
of Barytes, Chromate of Potash, Sulphate of Iron, Calc Spar,
Quartz, right and left, Iolite, Nitre, Rochelle Salt, Topaz, Tour- .
maline, &c. for exhibiting the system of rings by polanscope . each
104. Polished Calcareous Spar, exhibiting white double elliptic rings ...
10- n multiplication of coloured images
106. Fresnel's Rhombs
107. Microscopic Objects, cases of, 40 transparent 0 7 6
108. „ 11 36 opaque • y,
109° f „ prepared in balsam 12s. to 5 5 0
110' M large, for solar and
gas microscopes
HI, ,, in cabinets <£?>• &*■ to
These collections of objects consist of preparations of insects : their
larvae; the different parts illustrative of the varied construction of
their locomotive, prehensile, manducatory, visual, and other organs ;
dissections shewing the structure of the alimentary, respiratory, and
nervous systems- fossil infusoria-parts of plants— ferns -algte—
mosses, &c— Objects mounted in this way (as first described in the
•■ List of 2000 Microscopic Objects") are rendered transparent and
permanent.
120
112. Microscopic Objects, consisting of British Insects/arranged in con-
formity with their organization, with printed
names, forming an excellent guide to the study
of Entomology, in glazed cases, shewing the
_ entire classification at one view ... £5. 5s. to 21 0 0
113# » in cases containing 12 thin sections of woods,
neatly mounted, ABCD 0 6 0
"*' " » 30 „ A. B. C. exogens 0 15 0
"2* " " 20 " D. endogens
llb- » „ 90 to 200 (choice)
The endogenous woods are cut in two directions, and the exogenous in
three, so that the structure of the plant may be accurately seen • that
placed next the name is a horizontal or transverse section, the others
are longitudinal, the middle one being parallel to the medullary rays
(radial), and the end section perpendicular to them (tangental) Thev
afford excellent examples of the elementary structure of vegetables, and
exhibit most of the forms and disposition of the cellular and vascular
tissues, and woody fibres of plants, in situ.
117> >> thin sections of fossil woods 2s. to
®* " » cut in two or three directions
" » „ cases of 2 2 0
These sections are cut so thin, that they transmit light as readily as the
recent woods j and shew the form and disposition of the woody fibre
vascular tissue, medullary rays, glands, pith, &c.
" cases of, consisting of organic fabrics, viz.
flax, cotton, mummy cloths, &c. ...
121' " » botanical, to illustrate vegetable
organography
122* » thin Sections of Coal, Charcoal, Jet, Lepido-
dendrons, Flint with organic remains, Topaz
and Quartz with moveable fluids, Prismatic
Felspar, Hyperstene, Recent and Fossil Bone,
Turbinolia, .(Erolites, Limestone with organic
remains, &c
123- " consisting of the ashes of vegetables ............
124, » sets of minute crystals, for shewing coloured"
tints, black cross, dichroism, &c. by polarizing
microscope, (M. I.) neatly mounted
JJ?; " sets of test objects, (M. C. 144,) 7s. 6d. to 1 l 0
~°' » cases and cabinets, containing specimens se-
149 pi i on r lected from each of the above classes £2. 2s. to 50 0 0
1-7. .Blank fehdes, foi mounting objects, plain glass, 2 inch ... per dozen
„ bevelled edges 2 ,,
" » 3 ,, t)
plate glass, edges greyed 2 „
>> ,, 3 ,,
>> polished 2 „ ,,
" >> 5 ,, s
prepared with mica 2 „
" >» 3 ,, >,
.. ,. » circular, various sizes „
138. Blank Discs, for ditto, opaque, i inch diameter per eross
lo9- " » l-8th „ ... s
140. Thin Glass, l-30th to l-100th of an inch thick, for covering objects
BOOKS.
The Microscopic Cabinet, with coloured plates s> n 1a „
The Micrographia =i 0 18 0
The Natural History of Animalcules ?. ? 6
List of 2000 Microscopic Objects '.'.'.'.'.'.'."". 0
A Catalogue of British Insects, arranged accord\:ng'to'their organization".*" 0 I o
Ihe Microscopic Illustrations, a new edition, emended and enlarged , o lo <
130.
131.
132.
133.
134.
135.
136.
137.
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In the Press, price, to Subscribers, Eighteen Shillings,
THE NATURAL HISTORY
INFUSORIA;
WITH AS ABRWGEiir.ST OF
Bit 3nfu£f!on$t0trrr&rn
OF
C. G. EIIREXBERG.
ILLUSTRATED BY ENGRAVINGS OF ALL THE GENERA GIVEN IX THAT WORK IND
ORIGINAL DRAWINGS OF FOSSIL INFUSORIA,
BY F. BAUER, Esq., F.R.S.
BY ANDREW PRITCHARD.
In announcing to the public a new Work on Infusory Animalcules, some explanation
may be required, why the Author has departed from the system of arrangement given
in his "Natural History of Animalcules," published in 1834; the more especially,
after the very nattering reception that publication met with, not only in England, but
throughout Germany and France. At the time that Work was being prepared, in
which the arrangement is that of F. O. Muller, founded on the external characteristics
of these minute creatures, Dr. Ehrenberg's, derived from their internal organization, was
not complete; and drawings of 19 species only had appeared in this country. Hence
it was, that the Author adopted the former ; the latter is now preferred ; notwithstand-
ing which the opinions of naturalists opposed to it will be fairly stated.
Although descriptions of every known species will be given, it is not intended that
the forthcoming Work shall be merely a catalogue of dry and technical specifications j
for it will contain so many curious and interesting particulars respecting the extraordi-
nary forms, internal organization, locomotion, habits and instincts of these wonderful
creatures— together with the best methods of procuring and examining them under
the microscope— which, it is hoped, will render the Work as complete a History, as up
to this period it can possibly be made.
The recently-discovered Fossil Remains, as incorporated with the Flint, or heaped
together in countless myriads, forming vast beds or mountains on the surface of our
globe, will also be brought under review; and the whole illustrated by Engravii
SEVERAL HUNDRED INFUSORIA, highly magnified.
In translating and abstracting so technical and extensive a Work as the "Die
Infusionsthierchen," occupying, as it does, nearly COO large folio pages, many diffi-
culties would necessarily arise ; these, however, by the great assistance which has linn
rendered him, the Author has been able to surmount; and it is believed, thai whilst,
on the one hand, this Work will be disencumbered of long lists of synonymes and his-
torical references, so, on the other, it will comprise all those important discoveries,
which, as the arrangement depends upon them, it would be unjust and unwise to have
omitted.
With respect to the Engravings, on the execution of which the value of the Work
will so greatly depend, few words only need be Baid; since the Author's long c\-
ice, and the high character attained already by the Illustrations of bis '
Works, will he the best guarantee of what lie is' likely to produce. It may b(
however, to state, that the Examples of Genera will be entirely selected from the mag-
nificent Engravings of the "Die Infusionsthierchen;" and thai the Illustrations i
Fossil Infusoria, discovered since Ehrenberg's Work was printed, are from the handoi
F. Bauer, Esq., a gentleman whose skill in this exquisite art is beyond all comparison.
Thus, on the whole, it is presumed, that the Engravings of this Work will sun
accuracy, finish and colouring, all that have yet appeared : and the Author i
enough to hope, that the Manual will take its place as the Standard English W(
this interesting branch of .Natural History.
Subscribers' Names received at 162, Fleet Street, London.
Just Published, by Whit taker and Co., Ave Maria Lane, London,
price 10s. Gd.
MICROSCOPIC ILLUSTRATIONS
LIVING OBJECTS:
THEIR NATURAL HISTORY, ETC., ETC.;
muti) fttgmtins
CONCERNING THE MOST ELIGIBLE METHODS OF CONSTRUCTING MICROSCOPES,
AND INSTRUCTIONS FOR USING THEM,
BY C. R. GORING, M.D.
& $ciu (SUttton, cmcirtrctt & cttlanrcr/, SHutftratca" unth Colour^ <£i\%vnbii\$8,
BY ANDREW PRITCHARD, M.R.L,
HON. MEM. SOC. ARTS, EDIN.; AUTHOR OF "NATURAL HISTORY OP ANIMALCULES,"
ETC., ETC., ETC.
" Contemporaneous with the publication of the First Edition of this Work a new
Era sprung up in Microscopic Science, disclosing to the students of nature and diligent
investigators into her more recondite operations, an illimitable field for observation.
Antecedent to the period just alluded to, Microcosm might almost have been termed a
world of its own, wherein myriads of living occupants, countless in species as in indi-
viduals, 'lived and moved and had their being,' unperceived by the intelligent faculty
of man ; and wherein they are as assiduously and dexterously engaged in the business
of life as those whose famed exploits resound throughout the earth. The vast pro-
ficiency arrived at in the constructing of Microscopes, and more especially the invest-
ing those instruments with effective achromatic lenses — an achievement we believe
entirely attributable to the authors of the ' Microscopic Illustrations,' has thrown a
light upon this most interesting subject, that can never again be obscured. In this
Edition, emended and considerably enlarged, Mr. Pritchard has furnished over and
above his descriptions of Aquatic Insects, and the almost incredible metamorphoses
they undergo, a comprehensive sketch of the uses of the Microscope and all its recent
improvements ; and also an excellent illustration of its application to the various sciences
and useful arts, especially Geology, Botany, Animal and Vegetable Physiology. He has
further explained, in popular language, the theory wherein consists the superiority of
the achromatic over the common Microscope.
" In his additional chapters will be found, a practical account of the most approved
achromatic Microscope, for exhibiting the infinite variety of transparent and opaque
objects — all its apparatus — the mode of selecting magnifying powers suitable for the
purposes either of deep investigation or pleasurable amusement — the moveable stage —
the spring phial-holder for retaining plants and living creatures in such a position as to
render clearly perceptible the circulation through them — the polarizing Microscope, with
all the curious and beautiful phenomena elicited from crystalline bodies by the aid of
polarized light, including Mr. Talbot's experiments — the apparatus for dissecting under
the Microscope — the camera lucida, with the micrometer eye-pieces for drawing and
measuring of objects — the mode of illuminating on a black ground — a new method of
determining the forms of minute bodies, and observing the currents in fluids during
the process of evaporation : — all these, and various other highly-interesting subjects,
are so copiously treated of, and so accurately elucidated by means of Engravings, as to
render this Work a complete practical guide for using the Microscope, and constituting
it one of the most delightful and serviceable instruments for man, in promoting his
researches after truth." — Gateshead Observer.
" Impressed as we are with the high importance of this branch of science, and with
the great value of the improvements which these gentlemen have introduced, we looked
fonvard with the most sanguine expectations ; and we have now no hesitation in stating
it as our opinion, that Dr. G. and Mr. P. have both accomplished their difficult tasks
with the greatest success. The coloured Engravings are executed in such a masterly
manner, that they will themselves bear to be seen by the Microscope." — Brewster's
Edinburgh Journal of Science.
" The present publication cannot fail to recommend itself generally, for it is asso-
ciated with elaborate descriptions and beautiful coloured Engravings of a variety of
diverting and popular objects." — Journal of the Royal Institution.
Preparing for the Press,
1.
DESCRIPTIONS OE VARIOUS APPARATUS
FOR ILLUSTRATING THE
INTERFERENCE OF LIGHT.
2.
ILLUSTRATING THE
WONDERS OF THE MINUTE CREATION ;
WITH
Scs"m|)ttan$ at the Ohjerte,
BY ANDREW PRITCHARD.
1 By the beauty of the creatures, proportionably, the mightiness of the Maker of them
is seen." — Wisdom of Solomon.
The design of this Work is an attempt to elucidate those parts of the creation,
which from their extreme minuteness are known to us only by the aid of the Micro-
scope. So manifold and various are these productions, all equally wonderful and
beautiful in their kind, and alike indicative of the wisdom and power of " the Maker
of them" — so full of interest is the study of them, that there is no branch of Natural
Philosophy to which our attention may be directed with a greater promise of instruc-
tion and delight.
Whilst the press absolutely teems 'with Works explanatory of organic and inorganic-
bodies, might we not expect, that the Illustrations of these Works would chiefly result
from the personal observations of the Authors ? Such, however, is not the case.
Strange to say, they are chiefly copies. A series of original Drawings, therefore, illus-
trating a Work of this description, taken from the finest specimens of Microscopic
objects ; such as the minute structures of the animal creation — the respiratory apparatus
and various locomotive, manducatory, visual, natatory, and other organs of Insects
— portions of bone, skin, scales, &c, &c. — the structures of woods, plants, recent and
fossil, ferns, mosses, algae ; also, the manner in which the circulation is carried on within
them — the curious mode of aggregation in divers geological productions; and a mul-
tiplicity of other highly interesting matters, it is thought, will not be unacceptable to
the public.
From the number of years the Author has been occupied collecting his materials,
and the thousands of beautiful preparations which have passed through his hands, no
ordinary opportunity has been afforded him; and it is with this belief, that he now
comes forward with a Work on this branch of Natural Philosophy.
London .- Whittuker and Co., Ave Maria Lane.
ADDENDA TO LIST
OF
CONSTRUCTED BY
ANDREW PBITCHARD,
©[pTQga^K] aim© g^gTaeii B^iAiKnyjiFAigTr^siiigg
162, FLEET STREET, LONDON.
1. Pritchard's Apparatus for illustrating the Interference of Light, with
Telescope and 100 Screens s ' \^15 15 ()
I" - ditto, with 50 Screens .. .. .'.' "' ' jq 10 q
^' ditto Pocket Apparatus . . . . . ' 0 8 6
4- ~ improved Eye-piece Polariscope, with Reflector ' .'. 2 2 0
th^Jth! w-8irU1£e?t exhibits. the col°i"-s more intense, and the rings better denned
than the Slider Polariscope, invented some years ago by Mr. P. and now eeneraHv
used. It can be applied to any compound Microscope. generally
■ improved Polarizing Apparatus for the Microscope . . Ill g
»„a ?y Mr* P"'S "ew "'•'"'ge'pent of the Prisms, the field of view is greatly extended
and any eye-piece can be used. gieauy e.\ienuea,
— — — ditto ditto large Prisms and a double image one . . 4 4 0
lhe Apparatus §4 and 5 fitted to Microscopes . 9 ,., ,
8. Stereoscopes " 0 K f)
10 SwH^f111 Spri,ng^C1°,Cr' f°rfixing the SUn'S ima&e in any position 8 8 0
iu. Fntchards improved Gas Microscopes .. .. .. "=£18 to
}}; ~ ditto di"p with polarizing and interference Apparatus
l~- new portable Gas Generators and Holders ,
andSaL?^
13. Prism Telescopes for shewing the lines in the Spectrum
14. Pntchard s Vertical Microscopes, single, doublet and triplet £5 5s. to 10 10
not SLXJBLK! **** "' *" const™ted "ith thin piano, convex lenses, and
U\ T -—Achromatic Microscopes [see Microscopic Illustrations] ^15 to
16. Improved Magic and Phantasmagoria Lanthorns. . £1 12s. 63 and
Sliders of Astronomical, Natural History, Costume, and Comic subjects.
17. Selenite Ornaments and Wedges for polarized Light 0 7
Jo SailLS ?/ LenS6S f?r exhibiting Newton's coloured Rings .' .' 0 10
on p v i s ™Proved, dumPy single-image Prisms, each . . 7s. 6d. to 0 14
20. Pritchard's new Fine-Adjustment Microscope Bodies .. . ni
f^„This construction is simple, more precise in its action, and of more eeneral utilitv
than any contrivance yet invented for the purpose. general utility
21 . Microscopic Objects, Is. each and upwards, or in cases at 6s., 15s., 21s.and
These objects consist of thin sections of Recent and Fossil Woods Coal let PW
22. Specimen Cases, containing Examples of the above, each 8s. 6d. and 0 15 0
ACHROMATIC AND REFLECTING TELESCOPES.
OPERA GLASSES, Single, Double, and Solid.
SPECTACLES IN EVERY VARIETY OF MOUNTING, W.TH CRYSTAL AND CLASS LENSES.
ie) is aw s ss'® EissmTm,wwmi^T^a
BAROMETERS AND THERMOMETERS. DOUBLE IMAGE PRISMS
njEOMW RHOMBS. BARTON* IR1S BUTTONS. TOURMALINES. POLISHED CALCAREOUS SPAR
INTERFERENCE MIRRORS AND PRISMS.
^alamwg anir iflurosfroptc Styparattt* of all femoa.
}- Darkirr, Primer, s, Uruve Cottages, H jllowsy.
8 8 I)
7 7 n
0
3 13
5 5 0
'ii
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