UNIVERSITY OF CALIFORNIA
SAN FRANCISCO LIBRARY

HOW TO SEE

WITH

THE MICROSCOPE:

BEING

USEFUL HINTS CONNECTED WITH THE SELECTION AND USE
OF THE INSTRUMENT ; ALSO SOME DISCUSSION OF THE
CLAIMS AND CAPACITY OF THE MODERN HIGH-
ANGLED OBJECTIVES, AS COMPARED WITH
THOSE OF MEDIUM APERTURE; WITH
INSTRUCTIONS AS TO THE SELEC-
TION AND USE OF AMERI-
CAN OBJECT-GLASSES

OF WIDE APER-
TURES.

BY

J. EDWARDS SMITH, M. D.,

PROFESSOR OF HISTOLOGY AND MICROSCOPY IN THE CLEVELAND (O.), HOM-
EOPATHIC HOSPITAL COLLEGE; CORRESPONDING MEMBER or THE SAW
FRANCISCO, THE DUNKIRK, AND ILLINOIS STATE MICROSCOPICAL
SOCIETIES; MEMBER OF THE AMERICAN ASSOCIATION
FOR THE ADVANCEMENT OF SCIENCE, ETC.

ILLUSTRATED.

CHICAGO :
DUNCAN BROTHERS,

, 1880.

Copyrighted by

DUNCAN BROTHERS,

131 and 133 South Clark street,

CHICAGO.

30

DEDICATION:

TO
THE HON. P. H. WATSON,

WHOSE FRIENDSHIP HAS ENCOURAGED AND WHOSE PARTICIPATION HAS
GIVEN DOUBLE PLEASURE TO THE INVESTIGATIONS RECORDED
IN THESE PAGES ; THE TRUE FRIEND, AND THE LIB-
ERAL PATRON OF SCIENTIFIC EXPERI-
MENT, THIS LITTLE BOOK
IS DEDICATED
BY THE

AUTHOR.

1

PREFACE.

INTRODUCTORY AND APOLOGETIC AL.

In the spring of 1874 I received from K. B. Tolles,
Esq., (the well-known optician of Boston, Mass.,) a
one-sixth immersion object glass, which he requested
me to study carefully, and to report the results to him.

The angular aperture of this new one-sixth was said
to be 180°, and the objective was one of the lirst " du-
plex " or four-system glasses devised by Mr. Tolles, and
destined, in a few short months, to create quite a stir in
microscope circles.

Having, at that date, leisure at my command, and
being very much interested in the performance of ob-
ject glasses, I was very glad to give this objective careful
and prolonged attention. The result was, that after
thirty days' experience I had arrived at a settled con-
viction that Mr. Tolles had made a decided advance in
the construction and performance of microscope object
glasses.

Believing this experience of mine to be of value to
microscopists, I wrote a short account of the perform-
ance of this one-sixth, which was published in the Cin-
cinnati Medical News.

Shortly afterwards Mr. Tolles kindly sent me another
of the " duplex " or four-system objectives, this time a

10 PREFACE.

one-tenth. This glass also occupied my leisure time for
a considerable interval.

The performance of the one-tenth fully sustained the
high appreciation I had formed of the performance of
the duplex glasses. In some respects the work of the
one-tenth excelled that of the one-sixth.

The article published in the Cincinnati Medical News
was therefore supplemented by several other communi-
cations written by me, giving my further experience
with the duplex objectives.

Among the conclusions I had arrived at from the study
of the new four-system glasses were to be found em-
bodied ideas radically opposed to popular dogmas which
were at that date fully received and accepted by inicro-
scopists generally as settled matters of fact. For in-
stance, it was claimed for the duplex one-sixth and one-
tenth that either of these objectives would not only do
the work of, but excel the performance (under amplifi-
cations from 275 to 4,000 diameters) of any one-fiftieth
extant. Furthermore, it was claimed that the central
light work of the new wide apertured duplex objectives
would surpass that of the low angles.

Referring to the resolution of the severest test objects,
it was the express purpose of the said contributions to
the Cincinnati Medical News to claim and insist on, as
a stubborn fact, that the work of the duplex one-sixth
or one-tenth excelled that of any glass extant, " be it a
one-fifth or a one-fiftieth."

These, as well as other statements so thoroughly hete-
rodox to established belief, met, as a matter of course,

PREFACE. 11

with earnest opposition from my readers. A large cor-
respondence ensued, while many microscopists visited
me for the purpose of witnessing, by way of ocular
demonstrations, the performance of the duplex glasses.

Meanwhile, in London, England, a lively controversy,
known in microscope circles as " the war of the aper-
tures," appeared in the columns of the London Monthly
Journal of Microscopy, in which controversy the posi-
tions assumed by Mr. Tolles were assailed by Mr. F. A.
Wenham. The issues involved, however, appertained
only to optical possibilities, the performance of the du-
plex objectives being an entirely outside matter. During
the London battle Mr. Tolles was ably assisted by Dr.
J. ,T. Woodward, of Washington, D. C., and by Piof.
Keith of Georgetown. Suffice it here to say, that froir
the standpoint of optical science Mr. Tolles maintained
his positions, a fact, I believe, now generally admitted,

And now, after a period of nearly six years, it is to
me a matter of pride to here record that of the several
4 ' heterodox " positions I had assumed in public print,
there has occurred, neither in the interim, or at this
present writing, no occasion to retract one word of what
was claimed by me in my former contributions to the
Cincinnati Medical News. The duplex objectives have
steadily, and perforce of intrinsic worth, forced their
way into general use, while the leading opticians are
exerting themselves to still further improve their
performance.

Having, as I have above briefly set forth, had a very
large experience with the four-system objectives, it was

12 PREFACE.

suggested to the author that a small work, giving in
detail the manipulations of the new objectives, with,,
perhaps, some other items resulting from an experience
of over fifteen years as a microscopist, would not only
be acceptable, but would fill a place at present unoccu-
pied ; and it is in response to this suggestion this little
book is presented, with the hope that it may prove of
some service to some of my brother microscopists.

The book is entirely innocent of literary pretensions,
It has been my aim to express myself in the simplest
possible manner. The diction is at times redundant,
gossipy and commonplace, the dominant idea through-
out being to hold a good natured chat with my readers.

During the past eight years the author has received
thousands of letters asking for information in the mat-
ter of microscope object glasses, and especially has his
experience been called on as to methods of manipulation
involved in the use of wide apertured objectives. In
the following pages he has endeavored to supply this in-
formation, introducing, it is believed, the first attempt
to teach the difficult art of collar adjustment, as will be
seen in the graduated series of lessons, which, imperfect
as they are, it is hoped will nevertheless be of value to
those commencing to use the four-system objectives.

/Vnd now, by way of apology, it remains to state that
circumstances entirely unlocked for, and entirely beyond
the author's control, have caused a delay in the publica-
tion, and many have suffered disappointment therefrom.
This delay, however, has furnished me with the oppor-
tunity to revise the MS., rendering it, I trust, more

PREFACE. 13

acceptable. It has also given me the opportunity to
introduce new matter not originally contemplated.

During the period of delay above mentioned the- writer
was in receipt of hundreds of letters of enquiry from
as many kind friends. It was impossible to reply to all
of these. He, however, improves the present as a fit-
ting occasion to return his grateful thanks to those of
his correspondents for the tangible evidences of confi-
dence and esteem thus manifested.

And to the Messrs. Duncan Bros., too, is he under
obligations for the hearty manner in which they took
the little brochure under their wing, pushing the same
through the press with their accustomed energy.

323 Euclid Avenue, Cleveland, O., September 1880.

ACME STAND.

CONTENTS.

PAGE.

Introduction and Apologetical 5

CHAPTER I.

Something about American Stands, etc. . 17

Zentmayer's American Centennial Stands. ... 34

The American Histological Stand 39

Tolles' large kt B B " Microscope 47

Tolles' Largest " A " Microscope 48

Tolles' Student's Microscope 49

The Professional Microscope 53

Large Student's Microscope 46

Family Microscope ........ 57

Bulloch's First-Class Microscope 69

Small best Stand'1 A B" ....... 67

Mr. Bulloch's " D " Stand 67

Mr. Bulloch's New Biological Stand .... 68

E. &. J. Beck's Microscope 71

Beck's Popular Microscope, Minocular or Binocular . 72

Beck's Economic Microscope 72

Beck's New Histological Dissecting Microscope . . 79

The New National Microscope 80

The New Acme Stand 84

13

14 CONTENTS.

CHAPTEE II.

What is Augnlar Aperture 93

Angular Aperture ... ... 93

How Shall we Measure Angular Aperture ... 95

Object Glasses , 97

Something Further about Objectives .... 108

Balsam Apertures 123

Flatness of Field , 126

Mounting of Objectives . 129

Nomenclature of Objectives . . . . . 530

Table of the Magnifying Power of Single Convex Lenses 134 '

CHAPTER III.

Objectives Continued 137

Objectives of Lower Balsam Angle . . . .144

Adjustable Objectives . • . , . . . 345

Eye-Pieces 156

CHAPTER IV.

Manipulations — Wenham's Reflex Illuminator . . 157

The Woodward Illuminator ...... 163

Tolles' Traverse Lens ... 179

CONTESTS. 15

CHAPTER V.

Illumination 183

Sunlight .......... 186

Artificial Light 187

CHAPTER VI.

Choice of Objectives for Regular Work ... 202

Selection of Covering Glass 213

Bull's Eye Condenser 225

Working with Low Powers 225

The Spencer one-inch of 50° — Broad Guage Objectives,

etc. 230

CHAPTER YII.

Work with the Higher " Powers " 235

Position of Observer 246

Mean of ten Measurement of Moller Test Plates . . 253

Position of Observer 289

Work over dry Mounts with high Aperture Objectives . 298

Oil Immersion Object Glasses ....'* 309

Immersion Objectives 310

16 CONTENTS.

CHAPTER VIII.

A Word or two on Volumetric Analysis . . . 318

Apparatus necessary 320

Analysis of Urea, etc 325

Analysis of Sugar, etc 332

Preparation of Urinary Constituents 339

APPENDIX.

Names and Address of Dealers in Microscopes, Object-
ives, etc., Alphabetically Arranged .... 341

The Investigator Microscope 345

International Microscope Stand, 348

Prices of Accessories 352

SUPPLEMENT.

Contributions to the Cincinnati Medical News . . 358

High Angles , 359

Angular Aperture and Central Illumination ... 361

On the Performance of Objections 368

Angular Aperture once More 370

The use and abuse of the Microscope .... 375

A Chapter on Elementary Physics , 393

Choice of Objectives , , 397

Microscopical Examinations of Oleomargarine . . . 400

HOW TO SEE WITH THE MICROSCOPE.

CHAPTER I.

SOMETHING ABOUT AMERICAN STANDS, ETC.

The choice of a stand is a matter of interest to every
working microscopist, and to most of us it has been a
source of much annoyance and needless expense. It
may be safely affirmed that most workers have wasted
more money in previous purchases of unsatisfactory
stands than would suffice to pay for the one at present
in use ; very many indeed would feel grateful to be let
oft' with this record. I therefore propose to assist the
novice in the important matter of the selection of a
stand, and shall, with this end purely in view, give him
fearlessly what, in my opinion, will be sound advice.

And be it known again that there will be some adver-
tising done in this department. As 1 have before inti-
mated, it is quite impossible to say what I shall have to
say, of real value to the reader, without giving promi-
nence to one or more of the several makers. The re-
sponsibility is mine, and I accept it. It has been my
province, in times past, to select many stands for my
friends and acquaintances ; those who have visited me
with the special object to ascertain my methods of using
and working objectives have, in many instances, fol-

18 HOW TO SEE WITH THE MICROSCOPE.

lowed my recommendations as to stands, and in every
case, I believe, have expressed to me their satisfaction.
The author has not in the past stood so much alone as
to his ideas of a stand as was the case with his opinion
of objectives.

Now, in what follows, it is to be assumed that the
reader desires one stand, and one only, and that he
wishes to invest his money to the best advantage, i. e.,
make the same go as far as possible ; that he desires a
really good and reliable instrument, and one that will
last for a lifetime.

During the past three or four years, the microscope
stand has been greatly improved, both in Europe and
America, and as a rule, really serviceable instruments
can now be obtained either of American or London
workmanship, and at a moderate cost. It is to be re-
gretted that our German friends have not followed suit,
but, on the contrary, have been content with the old
form of stands which were patent ten years ago.

In the late improvements by' the American and Lon-
don makers, it is first noticealle that the weight of the
stand has been considerably reduced ; the old idea, that
to secure sufficient solidity it was necessary to employ
stands weighing from twenty to forty pounds, being
now practically abandoned.

Again, it was formerly considered a sine qua non that
the microscope stage be thick enough, heavy enough,
and solid enough to bear the whacks from a sledge-
hammer.

It must be here kept in mird that years ago there

SOMETHING ABOUT AMERICAN STANDS, ETC. 19

were no such things as wide-angled objectives, and, as
a matter of course, the work was principally done
with central or centrally disposed light. To this the
old and heavy stage offered no objection, for it was
quite possible, with the aid of achromatic condensers,
prisms, etc., to work with all the obliquity the objective
would respond to, using a stage two or three inches in
thickness. Luckily, there were those who would at
times "fight objectives," play with diatoms, etc., and
in response to their demands the optician increased his
angles and working force of the object-glasses. To meet
this in turn called for the construction of condensers of
greater angle; until finally it occurred that the aper-
ture of the objective had arrived at proportions to
which the condensers did not satisfactorily respond.
Something had to be done, and something was done,
for necessity is the " mother of invention."

The simplest way is the best, and this was to reduce
the thickness of the stage. The "fighter" of objec
tives had discovered the fact that a stage, one-fifth of an
inch in thickness, was solid enough for any and all of
the delicate work required by the microscopist, while at
the same time he derived a great advantage in thus pro-
viding play for the aperture of his objectives.

The writer remembers with pride that he " took a
hand" at this; he remembers, too, the unalloyed satis-
faction he experienced in seeing two heavy, lumbering,
and expensive stages, alone costing several hundred dol-
lars, removed from imported stands, and their place
substituted by plain, thin plates made by the local

20 HOW TO SEE WITH THE MICROSCOPE.

watchmaker; he recollects, also, the exclamation of
one of his friends, after looking at an object as dis-
played by the improvised stage : " Well, I declare !
This instrument was made for any thing in creation but
to see through."

Hence it was, responding to the increasing call, our
American and London makers decreased the thickness
of their stages. While it is yet true that many of the
present stages are unnecessarily thick, the reduction is
still palpably manifest.

It may be remarked, then, that the real improvement
of late years in the construction of American and Lon-
don stands may, as a rule, be manifested in these two
items, viz., reduction of weight and thickness of stage.

We have learned something from the Germans, too,
within the past few years. It has been well known
that they favored the vertical stand with its short tube.
Our experience has taught us that both of these have
their advantages, and our later instruments are so con-
trived as to be used with short, and also with standard
tube, and in a vertical or inclined position.

I desire in this place to record the fact that the stands
made in the United States are not excelled in any qual-
ity or condition going to make a number one, reliable
instrument. The stands produced by our home makers
are quite equal in every respect to those of any other
countries, while their cost is not one whit higher.

Those contemplating the purchase of a stand will, as
a matter of course, consult their individual taste and
inclinations to a considerable extent: thus, A may select

SOMETHING ABOUT AMERICAN STANDS, ETC. 21

a large and heavy stand, while B would prefer a smaller
and lighter one. The party, too, will naturally take
into consideration the particular field of work he may
have in contemplation. It is quite possible to give the
latter consideration too much weight. It will be found,
as a rule, better policy in the long-run to purchase a
stand capable of doing almost any work, and thus avoid
the possibility of being compelled to sell at some future
date, at a heavy discount, and purchase another and
more capable stand. Fortunate it is that one can now
purchase, at moderate figures, reliable and well-made
stands, suitable for almost any purpose of tl e micro-
scopist.

In the reference that has been made to American
stands, it is proper to state that the Messrs. Beck, of
London, have a regular agency here for the sale of
their wares, and that this agency is in charge of an
American gentleman. There can be no good reason to
regard them as other than home folks. At all events,
the author is of this opinion, and will act accordingly.

Among the essentials that deserve attention in the
selection of a reliable stand may be mentioned :

FIRST. See that the stand is well balanced in every
position that it manifests no disposition to topple
either one way or the other; that it stands tolerably
firm (for its weight) on its legs.

SECOND. If it has coarse adjustment by rack and
pinion, see that the movement is as smooth as oil;
reverse the milled heud between the thumb and finger
promptly, and notice if there be any lost motion; try

22 HOW TO SEE WITH THE MICROSCOPE.

this test all the way of the "run" of the rack, and if
there be " lost motion" detected discard the stand.

THIRD. Examine carefully the bearings on which
the body slides; these should be broad, and the fitting
of the body to the limb accurate; test by placing a
small object on the stage — a circular diatom will be the
thing; now examine with a half-inch glass; rack the
tube up and down a little, and see if the object keeps
its centre ; seize the body-tube near the eye-piece, and
twist it a bit from right to left, and vice versa, noticing
whether the object "travels" or not; repeat this ex-
periment by punching holes in a card-box, say three-
quarters of an inch thick, thus forming a supplemental
stage ; focus again and try the twist once more. The
instrument that will stand this test is all right as to its
bearings.

FOURTH. Place the diatom on the stage, under the
half-inch, as before, and if the instrument has fine ad-
justment by nose-piece, test by moving the fine wheel
quickly either way, and see if the object " travels." If
satisfactory with the half-inch, try an eighth, or tenth;
test also by taking hold of the objective as one would
in the adjustment for cover, by giving it a little twist
right and left, and see if the object changes its position.
Finally, examine the run of the fine adjustment; see if
it is quick and sensitive to the touch, without "jump;"
if satisfactory so far, so good.

FIFTH. Should the stand have concentric stage, test
the accuracy of its fittings with diatom and half-inch
glass. If the stand has suffered transportation, or has

SOMETHING ABOUT AMERICAN STANDS, ETC. 23

in any way been submitted to fatigue, the probability
will be that the stage has become somewhat decentred,
and any effort of your own to re-adjust will be likely to
make things worse. The very best stages will not
remain centred long if roughly used. Still, with your
half-inch and the diatom you can manage to get some
idea, which will be better than none at all. Centre
your diatom, and focus; now seize opposite edges of
the stage with both hands, hold it firmly, giving it
"jerks" either way, right and left, but not sufficiently
to absolutely move the stage on its centre. If you suc-
ceed in moving your object, with a corresponding move-
ment of the stage, then the latter is not accurately
fitted, and cannot be accurately centred. This "slip"
can be detected with the hands alone.

SIXTH. It the stand be furnished with mirror fitted
to radial arm, see that all these fittings are strong and
likely to last. This portion of the stand meets, with
more fatigue than any other. See that the friction sur-
faces are not both the same metal ; this will apply, too,
to any part of the stand. Notice particularly whether
the universal motions of the mirror are properly con-
structed, and likely to last for years ; this is a most im-
portant point.

FINALLY. It will be well to see that the joint for
inclining the instrument at various angles is strong and
well made, and that it have compensation for wear.
Notice the general «' get up" -the general finish of its
various parts. And now, having received a lesson on
the use of diatoms, you may put the little fellow away
until again wanted.

24 HOW TO SEE WITH THE MICROSCOPE.

Aside from these matters involving sound mechanism,
there remain other points connected with the choice of
a stand, which may, to some extent, be regarded as a
matter of election. For instance, some of the most
costly stands are furnished with mechanical stages
whereby motions are given to the object-carrier by
various milled heads. I have used these stages in times
past, anc1 have to record my disapprobation of them,
and for the following reasons:

FIRST. They are an impediment to quick work. It
is much quicker to run from one end of an object to
another by one single movement given by hand than
to wait the slow motions of the screws. There are, how-
ever, some advantages arising at times from the use of
the mechanical sta^e, e, g., in adjusting the image of an
object to the eye-piece micrometer, etc. Nevertheless
these slight conveniences are sadly outweighed by the
positive objection to their use.

SECOND. A mechanical stage, to be good for any
thing must be nicely made ; hence they are costly, and
further, seldom keep in order for a great length of time,
however well made.

THIRD. As generally modelled, they increase the
thickness of the stage, and the screws are always more
or less in the way.

FOURTH. Those who rely on their mechanical assist-
ance seldom arrive at that delicate finger manipulation
so necessary to be acquired by the observer. Any one
of the objections above named ought, in my opinion, to
be sufficient and determinate.

SOMETHING ABOUT AMERICAN STANDS, ETC. 25

Many of the first-class stands (so called) are fitted
with sub-stages, provided with rack and pinion, and
centering screws. In the latter models these accessories
can be completely removed, leaving the entire instru-
ment below the stage clear and unobstructed. Beyond
the cost which these appliances incur, I see no particu-
lar objection to their presence ; but the novice is in-
lormed that they are by no means a necessary adjunct,
-and that their duties can be performed by simple and
less costly contrivances.

Stands have lately been introduced with short tubes,
but capable, by means of an interior draw, of being
drawn out to the standard length of ten inches. This
is an improvement on the short tube of the German
school, and one of real value. The daily worker will
find the short tube a great convenience when working
over wet preparations, or dealing with reagents. Under
these circumstances, to work quickly one must needs
keep the stage horizontal and the tube vertical. It is
true that we can compensate, in a measure, in using the
standard lengths by working with a lower table ; but
in this case the observer cannot have his instrument so
well under control, and he is further compelled to re-
sort to some out-of-the-way contrivance by way of get-
ting rests for the elbows.

In the selection of a stand, I advise strongly that it
be fitted with a concentric rotating stage ; and should
the res angusta domi present no obstacle, let the stage
be a good one, divided to degrees, capable of an entire
revolution, and furnished with an object-carrier. The

26 HOW TO SEE WITH THE MICROSCOPE.

advantages ot the revolving stage are manifold, while
to the advanced worker, it is a sine qua non. In the
examination of difficult and resisting structures the ob-
server needs at times to employ almost every variety of
illumination, as well as to view the object under various
aspects. In this department of work the rotating stage
cannot be dispensed with.

Where money & an object, let the would-be purchaser
proceed with due care, giving this matter the closest
attention. By observing the following instructions he
can provide for a rotating stage capable of responding
to almost any call, and at an outlay not to exceed five
dollars. The writer has two stands. One is a large,
heavy, first-class instrument, and is, of course, furnished
with adjusting concentric stages, divided to half-degrees ;
the other is one of the smallest stands made, and is-
fitted with short tube (which can be drawn out to
standard length), and a plain, revolving stage, which
cost two dollars. Ninety -five per cent, of all his work
is done on the little stand; the work allotted to the
larger instrument being the measurement of the angles-
of crystals, recording of objects by the Maltwood finder,
and the measurements of the angular aperture of ob-
jectives. This much for the solace of those who are
bothered with the hard times.

In making the selection with the view in hand of
providing a cheap rotating stage, the first important
point is to see that the instrument has sufficient stage
room. The stage should measure one and seven-eighth
inches from the centre of well-hole to the nearest por-

SOMETHING ABOUT AMERICAN STANDS, ETC. 27

tion of the limb touching the stage ; and any instrument
having less distance than this will not answer for the
purpose, while a half-inch more room would be very
desirable. The object of all this is to get room enough,
so that we can employ a circular stage large enough to
work an object-carrier.

. Next, see that there are no sub-stage fittings, which,
by their particular method of attachment, will inter-
fere with the stage about to be described. Look the
ground over carefully, and, accepting that the road is
all clear, we proceed to describe the stage which the-
author has had in daily use for years, and one that has,,
to a considerable extent, been copied by his friends.
Any watchmaker or machinist can do the work — in
fact, one of my friends made one for himself.

Provide a sheet of well-hammered brass, heavy enough r
so that when planed or turned down the stage shall be
one-sixteenth of an inch in thickness, with both faces
truly parallel. Cut the circle which is to form your
stage as large as your instrument will permit, and in
accordance with the above directions.

Cut the well-hole one-sixteenth of an inch larger
than the well-hole of your stage ; make a collar, or
short tube, out of the same material used for the stage;
turn the outside to proper dimensions, so as to fit the
well-hole of the new stage, the upper edges of both
being " flush," and solder in position.

Next: Turn accurately the under and projecting part
of the short collar, or tube, so that it will exactly fit
the well-hole of your main stage ; place it thereon, and

28 HOW TO SEE WITH THE MICROSCOPE.

cut off any portion of the collar that may project
beneath said stage.

In the stage thus far towards completion, it so be
that the collar projects one-sixteenth of an inch, this
will be found ample for its support ; thus you will be
enabled with some stands to steer clear of sub-stao-e

o

appliances, etc.

All that remains to be done is to fit your new stage
with plain spring-clips, which can be done in a few
moments out of a piece of watch-spring ; or, if there is
room enough, you can provide an object-carrier, made
on Mr. Zentmayer's principle; all of which is plain
work, and easily accomplished by any machinist of toler-
.able skill.

Keep in mind that this stage adds somewhat to the
thickness, and govern yourself accordingly.

" But," says one, " I have no assurance that this stage
will rotate in the optical axis." I grant it, with the
remark that if it did so rotate with one objective, it
would be pretty sure to fail with another. The com-
pensation must be supplied by finger manipulations,
easily acquired, and as easily practiced. As I have
previously hinted, the best rotating stages remain con-
•centric but fora short time, especially if much used;
while to the real worker, the very bother of adjusting
the most expensive stage extant would be an intolerable
annoyance, and a willful waste of time.

A grand good thing about this improvised stage is,
that it can be placed in position or removed therefrom
in a moment's time. This, to the author, is a real boon,

SOMETHING ABOUT AMERICAN STANDS, ETC. 29

for he has often to remove the supplemental stage, and
to work for hours with the mounts placed on the main
plate, using not even the spring-clip or any other
attachment, the microscope being the while in the ver-
tical position.

Says another: Why not have the maker furnish
some such stage at the date of purchase ? He can da
these things better than any one else." I respond,
Yea, verily.

Thousands of times the question has been asked,.
" Which do you prefer — the binocular or the monocu-
lar? " and as it is more than probable that this question
will arise in the minds of some of those who read this
book, perhaps a word or two on the subject may not be
amiss.

Mr. Henry Crouch, F. E. M. S., a well known maker
of microscopes, visited this country during the Centen-
nial Exhibition, and on his return complained bitterly
of "an eminent German microscopist, who assisted in
examing the microscopes on exhibition at Philadelphia,
and who from the first loudly proclaimed the useless-
ness of binoculars, . . . but whom he afterwards
found out had never used one." The author is pretty
much in the same boat with the eminent German.

Since the introduction of the binocular, the writer
has made several downright square and honest attempts
to use the binocular long enough to be able to express
an opinion worth consideration, but in each and every
case the double barrelled machine proved too much for
his patience. With the low powers the instrument is

30 HOW TO SEE WITH THE MICROSCOPE.

capable of giving- very pretty shows, particularly where
a certain stereoscopic effect is supposed to add force.
Hence the binocular is eminently fitted for such dis-
plays, and is eminently adapted, too, for the entertain-
ment of those of our lady friends who visit the soirees
of microscopical societies, without feeling specially
interested in microscopy as a science.

If so be that there can be structure displayed by the
binocular that cannot be seen equally well by the mon-
ocular, be it so, and the author will joyfully add his
testimony to the same, after having arrived at the fact.

Many of my friends have binocular instruments, but
I can not recall the name of any person who uses one ;
that is, when I am present, for inevitably the first thing
<lone by the owner is to displace the prism, and to use
the stand as a monocular. I have never found a soli-
tary exception to this rule.

But some one may say: " What possible objection can
there be to purchasing a binocular, since, as you admit,
the instrument can be changed instantly to a monocu-
lar, and the purchaser has his choice. He certainly has
all that you have got, and perhaps (allowing force to
the opinion of others) more too."

Well, that looks lucid enough ; and in truth that
argument has sold many a binocular. Nevertheless,
" all is not gold that glitters." Let us take a look from
iinother stand point, thus :

First. The binocular involves greater weight ; as a
rule, they are unwieldly, lumbering things, destitute of
grace, symmetry, or aught that goes to make a clean,
well proportioned stand.

SOMETHING ABOUT AMERICAN STANDS, ETC. 31

Second. The binocular instrument is much more
complicated, and hence more expensive, the purchaser
fceing required to pay, without getting in return value
received.

Third. This form does not admit of the instrument
being used with short, as well as standard tube, and to
the " worker " this item has particular force.

Fourth. The extra expense attending the purchase
•of a binocular can be better applied in other directions.
Those who value dollars and cents will find force in
this objection.

Fifth. I oppose the binocular, because the monocu-
lar is good enough, and because the real work of the
microscope has been and will continue to be done with
the monocular.

Sixth. The binocular is to a certain extent impract-
icable, because the two eyes of the observer are not
alike. There are exceptions, but not to an extent suffi-
cient to invalidate the rule.

Seventh. I oppose the usual form of binocular
instruments, believing that the binocular eyepiece
invented and made by Mr. K. B. Tolles is a preferable
way of obtaining binocular vision.

Having thus presented my objections, let the reader
elect for himself, with this assurance on my part, viz.,
better get a good binocular than a poor monocular.

All stands should be furnished with plane and con-
cave mirrors. If the mirrors are attached to radial arm,
hinged at a greater or less distance from the under sur-
face of the stage, then it is apparent that when the

32 HOW TO SEE WITH THE MICROSCOPE.

radial arm is placed in position for oblique light the
mirror will be nearer the well hole than when the arm
is centrally disposed ; therefore, the mirror should be
arranged to slide on the arm, so that the proper com-
pensation may be effected.

The mirror should, of course, be well mounted in its-
own semicircular arm, so that universal motions may be
obtained, and the semicircle should be closely attached
to the slide moving on the radial arm; that is to sayy
there should be no intermediate, short, and jointed arm&
or elbows such as are found on many so-called first
class instruments, and are a most intolerable nuisance.
It is quite possible at times to remove these intermedi-
ate arms, and attach the mirrors directly to the radial
arm, and at a trifling expense, thus transforming a
faulty stand into a really serviceable one.

Examine the concave mirror carefully, as to its tocal
length. To do this, place a piece of white letter paper
on the stage, and using a common candle reflect the
light on the paper ; now move the mirror up and down
on the radial arm, and see if you can get a tolerably
well defined image of the flame. It may occur the
radial arm is too short for the focal length of the
mirror, and that it would be impossible to lengthen it
sufficiently; this being the case, reject the stand.

One would naturally suppose that an item like the
last would surely be attended to on the part of the
maker; nevertheless, many stands are made and sold
with glaring defects of this character.

At the risk of being tiresome, let me especially insist

SOMETHING ABOUT AMERICAN STANDS, ETC. 33

on the absolute importance of looking carefully to the
entire apparatus connected with the hanging of the
mirrors. This part of the mechanism is called to
endure more fatigue, and is oltener thus called on than
any other portion of the stand. For instance : In the
act ot observing, one often has occasion to seize the
mirror, and to move it and the radial arm by a single
impulse, simultaneously as it were ; and here let me say
that it will be well for the observer to acquire this
habit; nevertheless, it is terribly straining on the
joints thus called on, and they should be strong enough
to endure the fatigue.

See also that all the eye pieces slip in and out of the
tube easily; this too without decentring the object in
the field. Any difficulty in putting eye pieces in place
or removing therefrom is a first class botheration.

o

We now proceed to the description of the stands
made and sold by American makers. In placing Mr.
Joseph Zentmayer at the head of this list, the author
feels assured that he does no violence to the feelings of
others. Mr. Zentmayer was one of our earliest and most
energetic makers, and his work has, as a rule, proved
honest and reliable. In his expenditure of capital, his
facilities for execution, or his pride in presenting first-
class work, he stands second to none, as his competitors
will generally attest.

Mr. Zentmayer's largest and most costly stand has, I
may say, but just been placed on the market. It was
especially designed for exhibition at the Centennial
Exposition. The description which follows is to a con-

34 HOW TO SEE WITH THE MICRObCOPE.

siderable extent the same as that printed in Mr. Zent-
mayer's catalogue — some portions being suppressed,
and the wording occasionally changed at the election of
the author.*

ZENTMAYER'S AMERICAN CENTENNIAL STAND.

Constructed especially for the Centennial Exhibition.
It is mounted on a tripod, with revolving graduated
platform ; the bar and trunnions are in one piece, and
swing between two pillars for inclining the instrument
to any angle. The coarse adjustment is accomplished
by rack and pinion. Thus far it is similar to the
" Grand American Stand" by the same maker.

The swinging sub-stage, which carries the condenser
or other illuminating apparatus, including the mirror,
swings around a pivot, the axis ot which passes through
the object observed, so that this object is in every posi-
tion in the focus of illumination. The stage may bo
detached with facility, and replaced by one constructed
for oblique illumination; the swinging illuminator
may then (i. e., with the last-named stage) be used for
illumination from above.

The sub-stage is provided with a graduated circle for
indicating the degree of obliquity.

An object placed on the stage being in a plane with
the axis of the trunnions, it is obvious that if the in-
strument is placed in a horizontal position, the object

*In the several description^ of stands, that of the respective makers will
be given as far as possible. The author will, however, at his election, sup-
nress certain portions or change the diction as to him may appear desirable-

ZENTMAYER'S AMERICAN CENTENNIAL STAND. 37

is in the axis of revolution of the graduated platform,
and the angular aperture of an objective focused on this
object can easily be measured. It is equally obvious
that in this position the object is in the centre of all
the revolving parts of the instrument, to wit, the re-
volving stage, swinging sub-stage, and the platform.

The principal stage is similar to the circular one pre-
viously used on. the " Grand American;" it is provided
with adjusting screws for accurate centring, and re-
volves in a large outside ring, giving facilities for
oblique illumination up to 70 degrees from axis (140
degrees aperture), while the graduations serve as a
goniometer for the measurement of crystals, etc.

The sub-stage is divided into two cylindrical receivers,
to facilitate the adaptation of several accessories at one
and the same time ; the lower cylinder can be moved up
and down or entirely removed.

The fine adjustment (in all other instruments of the
Jackson model being in front of the body) is removed
to the more stable part of the stand. The bar is pro-
vided with two slides, one for the rack and pinion
movement, and close to it another one of nearly the
same length for the fine adjustment, moved by a lever
concealed in the bent arm of the bar, and acted on by a
micrometer screw. Thus the body is not touched when
using the fine adjustment, and the relative distances of
objective, binocular prism and eye-piece remain un-
changed.

O

The smaller stage of the American Centennial Stand
is also provided with screws for accurate centring ; this

38 HOW TO SEE WITH THE MICROSCOPE.

stage is three inches in diameter and extremely thin,
allowing, in connection with the swinging sub-stage
and mirror, not only the greatest obliquity of illumina-
tion, but the mirror and achromatic condenser will rise
above the stage when required, as in the case of sun-
light illumination, that of opaque objects, etc.

The diameter of the sub-stage is the same as that of
the " Grand American;" the accessories of that stand
are therefore interchangeable.

As to the general character of Mr. Zentmayer's work,
the author can affirm with confidence that it is not ex-
celled in any particular. The stand just described is
beautiful in design, is nicely proportioned, and in every
repect reliable and durable. It will stand all of the
tests named in the preceding pages. Those wishing a
first-class stand cannot fail to be satisfied with the Cen-
tennial.

The swinging sub-stage carrying the mirror, etc., is a
most valuable improvement, and one that the observer
can hardly afford to be without; the mechanism, too,
by which this end is accomplished is of the strongest
and most workman-like order.

Atcention also is invited to the method of attachment
of the stage. The latter is solidly held in position, or
can in a moment be detached, and another stage substi-
tuted.

It has occurred to the writer that the "principal
stage " mentioned might very well be dispensed with
the smaller stage being quite sufficient. Possibly a large
and plain stage might at times be found a convenience,

THE AMERICAN HISTOLOGICAL STAND. 39

this could easily be substituted for the more expensive
one furnished with the instrument.

As to the smaller stage referred to, the author can
" speak by the card." He had used one of Mr. Zent-
mayer's army hospital stands for years, and the instru-
ment gave him good satisfaction. Two years ago, how-
ever, desiring a thinner and a revolving stage, he begged
Mr. Zentmayer to devise one and fit the same to his
stand. Quite a correspondence ensued, and the army
stand was thus equipped, the new stage being practic-
ally the same as the small one furnished with the Cen-
tennial. It worked nicely, and was, in truth, all that
the author desired.

In the change of stages proposed, attention is called
to the fact that the smaller stage has not the graduated
edge. This to the majority of users would not be a
serious objection, while, on the contrary, many would
gladly avoid the cost of the graduated circle.

Mr. Zentmayer makes some eight or nine different
forms of stands. We have room to describe only one
other, viz. :

THE AMERICAN HISTOLOGICAL STAND.

The requirements held in view, in the construction
of this little instrument, were the combining of the
facilities of a first-class stand with moderate cost.

The entire instrument is made of brass, the base and
uprights are one piece, of a peculiar shape, and of great
rigidity, to which the bell-metal bar is attached by a

42 HOW TO SEE WITH THE MICROSCOPE.

joint, allowing the use of the instrument at any
of inclination; perpendicular and horizontal positions
are indicated by stops ; the coarse adjustment is accom-
plished by a sliding tube, the tube being but five and
one-half inches long, but capable of elongation to the
standard length.

The fine adjustment is similar to that of the Centen-
nial — a concealed lever moving the entire body ; this
adjustment is reliable and very delicate. The sub-stage,
plane and concave mirrors, swing in the same manner as
•do those of the Centennial, having the object in its
centre, even when swung over the stage.

The sub-stage carries the diaphragms, of which three
.are furnished with the instrument. Any piece of sub-
stage apparatus, such as condensers, paraboloids, prisms,
in fact anything from the lists, can legitimately be
adapted to the sub-stage, or the same can be instantly
removed, with the mirror also, if desired, thus leaving
the stand free from any obstruction below the stage.

The sub-stage slides up and down in strong dovetailed
grooves, and has centering adjustments by hand. The
weight of this little stand I judge to be about three or
four pounds; it can, on a pinch, be carried in one's
great-coat pocket.

It is worthy of mention in connection with these two
stands of Mr. Zentmayer's, that the fine adjustment
has been removed from the front to the rear, or, as
Mr. Zentmayer says, " to the more stable part of the
instrument." The author, when his attention was first
called to these stands, regarded this change of the fine

THE AMERICAN HISTOLOGICAL STAND. 43

adjustment as one of doubtful utility; and he once
made the remark to a friend, that should he purchase a
Centennial, he should insist that the maker furnish a
fine adjustment, both front and rear.

Certain it is that, in the process of correcting a first-
class wide-angled objective, it is a convenience to have
the fine adjustment at the trout. It is, however, ex-
ceedingly difficult to so accurately fit the sliding iiose-
piece that it shall move up and down with perfect free^
dom when acted upon by the fine screw, and at th(
same time to be free from lateral motion, and this
lateral motion constitutes a first-class fault to which
the attention of the reader has been called on another
page. The very best makers have found it difficult to
steer clear of this. The writer once met with one of
Mr. Zentmayer's larger stands exhibiting this defect in
a marked degree. His own " Grand American Stand, ''
however, in this respect, is faultless.

Thus it will be seen that, in the nature of things, a
really fine adjustment acting on the nose-piece involves
skilled labor, and this, in turn, involves cost.

Again, the movable nose-piece necessarily changes
the length of the body-tube, and this, in turn, again,
changes the amplifying power of the objectives, and to
get rid of this is indeed " a consummation devoutly to
be wished."

Having had the little Histological in constant use —
e. e., from six to ten hours daily — I arn now prepared,
from my own experience, to state that I am quite well
satisfied with the fine adjustment as placed by the

44 HOW TO SEE WITH THE MICROSCOPE.

maker. It would probably take me a trifle longer to
adjust nicely an objective on the Histological, and but a
trifle; while, on the other hand, all the objections con-
nected with the adjustment at the nose-piece are
avoided.

The Histological, as furnished by the maker, has
simply a plain stage with spring-clips. This defect did
not pass unnoticed by the writer, Mr. Zentmayer re-
sponding promptly to his request with the improvised
stage described on a preceding page.

It remains to be noticed that the Histological has
neither rack nor pinion,* and that the coarse adjustment
is effected by sliding the body within an adjustable
"jacket." There is no novelty in this, for the sliding
tube is "as old as the hills," and has been extensively
adopted in the construction of cheap stands.

The author felt very much like kicking at this feature
of the Histological. In a little time, however, experi-
ence taught him that the sacrifice of the rack and pinion
was not such a serious matter as might be supposed.
The sliding movement of the body tube within its-
jacket in the little stand is very smooth, regular, and
reliable, while, on the other hand, there are some ad-
vantages accruing to the slide that are not to be ob-
tained by the use of the rack and pinion.

For example: suppose we are working over wet
preparations, and unfortunately the front of the objec-
tive becomes immersed in the liquid — a misfortune

*Mr. Zentmayer now furnishes the Histological, with or without the
rack and pinion coarse adjustment.— AUTHOR.

THE AMERICAN H1STOLOGICAL STAND. 45

liable to occur daily. It is then, in such cases, a posi-
tive convenience to be able to pull the body-tube out of
the jacket, cleanse the objective, and return to its place.
All this can be done in much less time than would be
required, were the instrument furnished with rack and
pinion, to unscrew the lens, cleanse, and screw in place
again.

The greatest objection that the writer has to urge
against the Histological stand is this: When it is
placed in a vertical position, there is a liability of its
tipping forward. This can be prevented by clamping
the instrument to the table with a small iron clamp,
such as are used by carriage-builders and are sold at
the hardware shops for a dime. In this simple way the
stand is rendered as solid, more stable indeed than those
of the heaviest build.

One of my correspondents, to whom I had stated the
above-mentioned objection, informs me that Mr. Zent-
mayer has made some changes in the foot, securing
thereby greater steadiness.

Previous to the introduction of the Histological, it
was generally taken and accepted that the purchaser of
a cheap stand ought not, in the nature of things, to
expect an instrument capable of all work. To a slight
extent, and to a slight extent only, does the remark hold
good to-day, for the Histological has not the revolving
platform, for the measurement ot angular apertures
(apertures can, however, be measured on the stand),
nor has it the circular graduated stage; nevertheless,
the Histological will accomplish a larger variety of

46 HOW TO SEE WITH THE MICROSCOPE.

work than can be performed on the " Grand American
Stand " of the same maker, and this, too, be the char-
acter of the work what it may, be it the study of a
Histological object or the display of the No. 20 of the
Moller plate, or the 19th band of Nobert.

As may be arrived at by the tenor of the preceding1
remarks, the author regards the introduction of the
histological as marking an era in the progress of micro-
scope stands. The long-sought problem has been solved,
and in the Histological we have a cheap, reliable, and
universal stand, suitable for almost any work which
may be required, and capable of carrying any and all of
the various accessories which in the past have been sup-
posed to pertain only to the heavier and (so-called)
first-class instruments.

Furthermore, the author desires in this place to put
on record his unfaltering opinion that, in the devising,
construction, and introduction of the Histological stand,
the maker has bestowed a greater boon on the " body
corporate " of microscopists than has been accomplished
by others, either at home or abroad. If there be an
error in this statement, " time, with its revenges, will
set it forth."

TOLLES LARGE " BB" MICROSCOPE.

TOLLES' LARGE "BB" MICROSCOPE.

This instrument was designed to meet the require-
ments of the scientific investigator. The instrument,.

constructed on the Jackson model, is eighteen inches
high, when placed in a vertical position, and weighs
about fourteen pounds. The curved arm is supported
on a steel trunnion between two strong brass pillars

48 HOW TO SEE WITH THE MICROSCOPE.

made for durability, and not liable to get out of order,
and is provided with means ot compensation for wear.

It has rack and pinion for coarse and micrometer
screw for fine adjustment, the latter being placed in
front of the body, as has been usual in first-class instru-
ments, on the Jackson model. It is furnished with
graduated draw-tube ; sub-stage with rack and pinion,
and centring screws for accessory apparatus ; plane and
€oncave mirrors on double-jointed arm; Tolles' thin
stage, admitting light of great obliquity ; with rectan-
gular movements by screw and rack and pinion, and
rotation on the optical axis of about 270°.

Mr. Tolles makes a modification of this sized stand,
the stage being carried by friction rollers, and having
entire rotation on the optical axis. The cost of the in-
strument is thereby somewhat enhanced.

TOLLES' LARGEST "A" MICROSCOPE

weighs twenty pounds, and is one of the largest and
most solid instruments extant. The stage is six inches
in diameter, and makes a complete revolution on the
optical axis. The whole instrument rotates on a stout
plate graduated to degrees, and is similar in all respects
of style and construction to the " B" stand.

Either of the two stands named, made by Mr. Tolles,
may be unhesitatingly pronounced first-class. The work-
manship is of the very highest order ; the circular stao-e
can be so nicely adjusted as to allow of an entire revo-
lution, under a one- twenty-fifth objective, without the

TOLLE'S STUDENT'S MICROSCOPE. 49

object being sensibly displaced. Either form of stand
can be fitted with radial arm to carry accessory appar-
atus at any angle. Any thing that Mr. Tolles makes
is sure to be made well.

TOLLES' STUDENT'S MICROSCOPE.

This stand is fifteen inches high, weight six pounds;
the base, uprights, and curved arm are of iron, hand-

somely japanned. On a trunnion joint, made on a plan
to wear well, the instrument can be placed in any posi-
tion, from vertical to horizontal, and has a stop to pre-
vent movement in either direction beyond these points.
The stage is plain, with spring-clips for holding the ob-

50 HOW TO SEE WITH THE MICROSCOPE.

ject slides ; revolving diaphragm ; concave mirror, with
movement to give oblique light, and for the illumina-
tion of opaque objects the mirror is removed to an up-
right stand. The coarse adjustment for focus is effected
by sliding the compound body which is held in its place
by a spring; fine adjustment by a movable plate and
screw on the stage, which is efficient with high powers.
. The stand is made with all the care bestowed on his
•first-class instruments. The form is that of the Jackson
pattern. To this instrument Mr. Tolles supplies several
variations and additions, as a matter of course increas-
ing the cost as well as its capacity. Among these sev-
eral extras may be mentioned sliding stage, giving ver-
tical and horizontal motions by hand, and adapted to
the use of the " Maltwood Finder;" sub-stage for acces-
sory apparatus; fine adjustment by lever and microm-
eter screw; rack and pinion for coarse adjustment ; thin
glass stage to rotate on the optical axis ; the stand en-
tirely of brass, etc. For a " student's stand " this is an
instrument of good round proportions. It stands firmly
on its legs, and the stage is remarkably roomy. The
body-tube is nickel-plated, and the entire instrument
symmetrical in its proportions, and not without pre-
tensions to style. Like all of Mr. Tolles' work, it is
made " for keeps." There are many of them in use and
doubtless giving satisfaction.

The Bausch & Lomb Optical Company manufacture
several excellent stands, which were designed under the
immediate superintendence of Mr. Earnest Gundlach.
The firm furnish some seven or eight models, Irom
which we select the folio wins: three :

THE PROFESSIONAL MICROSCOPE. 53

THE PROFESSIONAL MICROSCOPE.

This is the largest and most expensive instrument
made by the company, and may be described as follows :
Heavy brass foot and pillars, both highly finished,
carrying the axis for inclination of the body, which
movement can be easily tightened or loosened by two
strong milled-head screws. Coarse adjustment by rack
and pinion, moving along prisma,tic slide, of first-class
workmanship, attached to the body; fine adjustment by
a new and patented frictionless motion. The object
slide rests upon a newly devised carrier ; the body tube
has an inner draw tube, with society screw to which ob-
jectives of very long focal distance can be attached ; large
plane and concave mirrors ; sub-stage for receiving acces-
sories of standard size, and two revolving diaphragms,
one of the latter belonging to the condenser ; all attached
to the swinging mirror bar, the axis of. which is placed on
the level of the object so that the diaphragm and mirror
swing concentrically around it. The mirror as well as the
sub-stage can be moved on the miiror-bar to and from
the object, and both can be removed, the latter by a hor-
izontal prismatic slide. The sub-stage ring is provided
with internal " society screw" for objectives, condenser,
etc. There are also two slot diaphragms of different
widths, covering the whole surface of the mirror, and
only allowing light to pass through the slot in such a
direction that very sharp shadows by oblique light will
be produced.

i J

56 HOW TO SEE WITH THE MICROSCOPE.

LARGE STUDENT'S MICROSCOPE.

Heavy japanned cast-iron foot, with highly finished
brass pillars, carrying- the axis for inclination of the
body ; brass arm ; coarse adjustment by rack and pinion ;
fine adjustment by a new and patented motion. The
special advantages claimed for this new adjustment are :
(1) exceedingly easy and smooth movement of the fine
screw both ways; (2) perfect freedom from all lost
motion; (3) perfect freedom from any side motion of
the image; and (4) extraordinary durability.

The microscope is provided with a movable slide
holder, serving as a substitute for a mechanical stage.
This slide holder consists of a German-silver plate of
very light weight, moving on a strong glass plate which
forms the immovable stage ; only four small points of
the German-silver plate touch the top of this glass
stage, while two prolongations of the former, bent
downward and backward, and acting as springs, press
against the underside of the glass plate with just suffi-
cient force to keep the slide holder in position, and to
prevent it from slipping off when the instrument is
inclined. Two small knobs facilitate the handling of
this slide holder, and it is claimed that this arrange-
ment exceeds in smoothness and evenness of motion the
movable glass stages commonly used, while the mova-
ble part has less weight, and allows the glass plate to be
of sufficient strength to guard against easy breaking.

The instrument has also plane and concave mirrors ;
sub-stage of the extra size required to receive standard

FAMILY MICROSCOPE. 57

sized English accessories; revolving- diaphragms, etc.
These are all attached to the swinging mirror bar, the
axis of which is placed at the level of the object, so that
the diaphragm and mirror swing concentrically around
the object. The mirror can also be moved on the mir-
ror bar to and from the object, and the distance between
the latter and the sub-stage can be varied by reversing
it. Both sub-stage and mirror can also be removed.

It is to be observed that in these two instruments the
importance of the swinging bar, before described in
connection with the Centennial and Histological stands
of Mr. Zentmayer, has been recognized by Mr. Gund-
lach. The mechanism, however, by which these makers
accomplish the swing in the plane ot the object, is by
no means the same in their respective stands. Thus the
peculiar method of securing the stage to the limb, em-
ployed by Mr. Zentmayer, allows that the sub-stage
with its accessories, and the mirror, be brought entirely
above the stage, the only thing preventing &full revo-
lution being the body tube, while in the instruments of
Mr. Gundlach the swinging-bar plays in a slot cut in
the rear of the main stage plate, and the swinging
motion is thus circumscribed by the stage slot.

FAMILY MICROSCOPE.

This has japanned cast-iron foot and pillars support-
ing the axis which carries the body, so that it may be
inclhied to any angle revolving diaphragm below the
stage; rack and pinion for adjustment of focus; con-

58

HOW TO SEE WITH THE MICROSCOPE.

cave mirror, adjustable for oblique light; plain stage
with spring clips.

Cf/»Vf«

This, although the least expensive instrument made
by Mr. Ghmdlach, is nevertheless well put together,
strong and really serviceable, and, with proper care,
ought to last a lifetime. It can be readily made capa-

the above was written, we learn that Mr. Gundlach has
separated from the B. & L. optical company, and that he now devotes his
entire attention to the manufacture of object glasses, the Messrs. Bausch
& Lomb, however, continued to furnish both stands and objectives, and ar&
by purchase, the proprietors of many of Mr. Gundlach's patents.

BULLOCK'S FIRST-CLASS MICROSCOPE A 1. 59

ble of doing most ot the work required by the physician
and to those who can afford the luxury of having two-
stands something of this kind will be found a real con-
venience.

Mr. W. H. Bulloch, of Chicago, manufactures seven
different forms of stands, from which we present the
following :

It has the concentric, rotating, and mechanical stagey
with graduations for measuring angles ; is also adjusta-
ble, so that it can be accurately and perfectly centered.
There are also graduations connected with the horizon-
tal and vertical movements of the stage, by which the
exact position of an object can be noted and found with
more certainty than with the " Malt wood Finder."
The whole stage is sufficiently thin to admit an angle
of oblique light as high as 134 degrees, and, if required,
the stage can be made reversible.

The sub-stage is fitted with the most complete move-
ments for centring or for oblique light with the achro-
matic condenser. It has one-fourth inch movement
each way ; rack and pinion ; divided circle for polariz-
ing; is so arranged that the sub-stage can be used
either above or below the main stage, and can be oper-
ated by hand or by tangent screws ; it is entirely separ-
ate from the mirror, but if desired .can quickly be
connected, so that the mirror and sub-stage turn

60 HOW TO SEE WITH THE MICROSCOPE.

together around the same centre, which is the thickness
of an average slide over the stage.

The entire sub-stage with its milled heads can be
taken off, so that there shall be nothing in the way
when using direct light. The mirror is arranged so
that it can be used in any direction, backward, forward,
over or under the stage. The mirror and also the sub-
stage have graduated circles, so that the obliquity can
be noted.

The movement of the bod}7 is effected by rack and
pinion connected with two milled hea^s, which connect
with the lever of the slow motion, thus preserving the
distance between the objective and the eye-piece. The
slide on the body tube is long and broad, thus prevent-
ing vibration or lateral motion when using the milled
heads or the micrometer SCTCAV ; the latter is grooved
so that it can be used for photographic purposes.

The instrument is mounted on tripod base, with re-
volving platform. The platform is graduated, and upon
it two standards are fixed, between which the instru-
ment turns to the angle when so used, or turning hori-
zontally for drawing, or for measuring angular aperture.
The centre on which the instrument turns, when placed
horizontally, is in a direct line with the object on the
stage.

The binocular model is arranged with rack and pinion
for different width of eyes ; the prism is so fixed that
the distance remains the same. The society screw at
the end of the body is arranged as a safety nose-piece,
with spring, so that the danger of breaking slides is

BULLOCK'S FIRST-CLASS MICROSCOPE A 1. 63

avoided. The iris diaphragm has the society screw so
that any objective can be used for a condenser, or it
€an be used above the objective as an adapter, to reduce
the light in the instrument. The stand is nineteen
inches high when arranged for use.

This stand and the " Centennial " of Mr. Zentmayer,
may be considered as rival instruments, and neither of
them enters the list for a slow race ; both are respec-
tively the masterpieces of their makers, and are claimed
to be the very embodiment of all and singular that can
be desired by the microscopist.

Purely in the interest of the reader, we proceed to
compare these stands with each other ; the final verdict
shall be left a matter of individual election.

First. The price of both instruments is precisely the
same, while the Bulloch has additional the iris dia-
phragm, the mechanical stage with its adaptations for

64 HOW TO SEE WITH THE MICRObCOPE.

use as an object finder, the safety nose-piece, the duplex
arrangement of sub-stage and mirror arm, whereby
these move in unison, or independently of each other r
and the centring and rotating sub-stage.

To meet this, it might be claimed, on the part of the
Centennial, that the above-named additional contri-
vances have been purposely discarded by the maker of
the Centennial ; that really there is no particular advan-
tages to be derived from the iris diaphragm, the mechan-
ical stage, the centring sub-stage, or the duplex
arrangement above referred to, and that all these con-
trivances serve unduly to complicate the instrument.

As to the centring sub-stage, it might be also said
that with the introduction of the "swing" there is no-
longer need of wide-angled achromatic condensers.
Furthermore the secondary body of the Centennial
being itself accurately centred, there is no occasion to
introduce especial appliances for this purpose.

It will be noticed that in the Centennial the mirror
and sub-stage rise without hindrance above the stage,
the movement being only stopped by contact with the
body tube (supposing the smaller stage to be employed,)
all this time the mirror remaining in fixed focal posi-
tion. To accomplish the rise of the mirror above the
stage in Mr. Bulloch's stand, the jointed arms connected
with the mirror are brought into play, and indeed can-
not be dispensed with. A close comparison of the
mechanism will reveal the fact that in respect to the
swinging arrangement, there is a wide difference in
the construction of the two instruments. The angle of

MR. BULLOCK'S " D" STAND. 67

obliquity obtained with the Centennial stage, is greater
than that obtainable in Mr. Bulloch's stand.

The principal points are thus presented ; it remains
for the reader to use his own election. Either of the
two stands will bear comparison with any foreign stand
extant.

Mr. Bulloch also supplies another stand, which he
calls his

SMALL BEST STAND " A-B."

This instrument is similar in construction to the
large stand, but smaller, excepting the body tube,
which is of the standard length in all his instruments.

MR. BULLOCH'S "D" STAND.

This has been selected by the author for description
principally because it is a medium-sized " student's
stand," and furnished with a concentric adjustable stage,
it being desirable to present as much variety as possible
within our circumscribed limits.

The adjustable concentric stage can be centred to any
objective ; the edge of stage is bevelled and graduated,
so that angles of crystals can be measured ; it has a
complete revolution. Its glass stage is perforated in
the centre, has brass fittings, so that the "Maltwood
Finder " can be used ; and its motion is perfectly smooth
under the highest power. To the underside of stage is
fitted a tube for accessories; this can be removed so
that the utmost angle of oblique light can be obtained.
Plane and concave mirrors and lateral motion for ob-

68 HOW TO SEE WITH THE MICROSCOPE.

lique light, coarse adjustment by rack and pinion, fine
ditto, by delicate screw, diaphragm; draw tube gradu-
ated, with society screw at end. The instrument can
be inclined to any angle, has English horseshoe base,
and is sixteen inches high when arranged for use.

BULLOCK'S NEW BIOLOGICAL STAND.

The cut shows the instrument about two-fifths the
real size, it stands twelve and a half inches high, and
the stage three and a half from the table when in an
upright position. Body tube five inches long, draw
tube five inches long; with marked ring when drawn
to the standard length. Standard size and sub-stage
fitting, adapted in sub-stage with the society screw for
the use of objectives as condenser, and the diaphragm
fits in the same screw and can be used1 close up to the
object slide. Plain and concave mirrors each swing
over the stage can be used together, or separate, can
be clamped in any position, by milled screws shown
behind the limb. Spring 'stop to mirror and sub-stage
when in line axis. Concentric revolving stage, can
be adjusted concentric to the axis by means of capstan-
head screws, the sub-stage also can be adjusted con-
centric by means of capstan screws. Spring clips to
stage or the sliding glass stage as desired.

When the stage is not required to revolve, it can be
clamped in any position by the milled screw shown in
front; and when there is any danger of injuring the
stage by the use of acids, the stage lifts out of the ring
in which it revolves, and any" ordinary piece of glass

B. & j. BECK'S MICROSCOPES. 71

can be used on the ring by placing the instrument in an
upright position. Rack and pinion quick motion, lever
fine motion placed behind the limb moving the whole
body tube; the body tute is fitted with broad gua^e
screw one and a quarter inch diameter, and in which
fits adapted with regular society screw, tripod base
with single pillar, the axis on which the instrument
turns is placed in such position that the instrument is
perfectly balanced when placed in horizontal position
for drawing. When so placed the centre of eye-piece
is seven and a half inches from table, the standard is
lurnished with a B eye-piece. The mirror and sub-
stage can be fitted with divided arch for measuring the
obliquity of light, the sta^e can also have divided circle
for measuring the angle of crystals. Stand all made of
polished brass.

R. & J. Beck, of London, the old and well-known
firm, have established an American agency in the
United States. In their facilities for the production of
first-class workmanship they are not excelled. As
makers of London instruments, they have been long
and favorably known, and the Londoner points with
commendable pride to the names of Ross, Powel, Lea-
land, and R. & J. Beck.

No attempt can be made in these pages to describe a
tenth part of the stands manufactured by the Messrs.
Beck. Their catalogue will be found to include all the
various grades, where may be found elegant and expen-

72 HOW TO SEE WITH THE MICROSCOPE.

sive stands, which, with the accompanying accessories,
etc., cost $1,600 and upwards, down to the more simple
forms, within the reach of all. It is from the latter
that we make the following1 selections :

BECK'S POPULAR MICROSCOPE, MONOCULAR OR BINOC-
ULAR.

In this stand the arrangement for changing the angle
of inclination of the body is new and durable. It has
coarse adjustment by rack and pinion, fine adjustment
by micrometer screw ; the stage is fitted with improved
object-holder and concentric revolving fittings; the
mirror slides on the main stejn, and has its own semi-
circle for universal motions. A diaphragm is provided
with perforated revolving disk. The instrument is on
the "transverse arm" model, which has been so ex-
tensively used by Ross, of London, as well as others.

The instrument caii be furnished with all the usual
accessory apparatus as supplied by the makers; a
mechanical stage, giving horizontal and vertical motions
by screws, is also furnished if desired.

BECK'S ECONOMIC MICROSCOPE.

The makers say in their catalogue that " the micro-
scope is now such an absolute necessity for the student,
to enable him satisfactorily to carry on his investiga-
tion, that it is more than ever incumbent on the optician
to construct a sound economic instrument adapted to
the special requirements of this large and increasing
class."

To this proposition let this little book say, Amen.

FU3JL

BECK'S ECONOMIC MICROSCOPE. 77

" For ordinary pathological, physiological, and botan-
ical investigations, many of the delicate adjuncts applied
to the higher-priced instruments are unnecessary, and
tend rather to contuse than to assist the beginner."

To this let these pages say again, Amen.

" A firm stand and well-corrected object-glasses are,,
however, indispensable."

In response to this we not only say amen, but shall,
in the proper place, have something further to add.

6 'The stand of the "Economic" is made in two
forms : the one with a sliding adjustment for focussing
the object, and the other where the quick movement is
produced by rack and pinion. On both stands the fine
adjustment is given by means of a milled head at the
top of the stem. The stand is fitted with the society
screw.

The foundation of the stand is a heavy horseshoe
base A, at the head of which is a firm pillar B, having
at its top a hinge joint C, which allows the body D to
be inclined to any angle, and is sufficiently firm to per-
mit of its being;* placed horizontal for use with the
camera lucida.

The body tube is short, but by means of the length-
ening draw tube V can be made of the standard length.

In the more expensive stand the coarse adjustment is
by rack and pinion; in the cheaper instruments the
quick movement is produced by sliding the body D up
and down the tube H, sliding over the inner stem with
a spring inside, the fine adjustment being accomplished
by the milled head I.

78 HOW TO SEE WITH THE MICROSCOPE.

The stage K, upon which the object is placed, has
two springs LL, the pins attached to which may be in-
serted in any of the four holes on the stage, and by
their pressure, which can be varied, they will hold the
object under them, or allow it to be moved about with
the greatest accuracy.

The mirror M, besides swinging in the rotating semi-
circle N, attached to a bar O, with a joint at each end,
allowing a lateral movement, so as to throw oblique
light on the object, and for this purpose the tube
beneath the stage, carrying the diaphragms, has semi-
circular openings cut on either side, leaving a clear and
thin stage, allowing the utmost obliquity of illumina-
tion. This tube also carries the polariscope, etc.

The diaphragm P slides in the sub-stage fitting, and
consists of a tube containing two caps furnishing two
sizes of openings, immediately in contact with the
under surface of the slide to be examined, and also
completely cutting off all light from the mirror, when
opaque objects are to be viewed.

The instrument packs, without being taken to pieces,
in a small and neat case, is very convenient for travel-
ing purposes, and entirely adequate for very many pur-
poses. The general workmanship seems in keeping
with the reputation of its makers, while its cost places
it within the reach of all. At an advanced cost, it can
be supplied with all the usual accessories.

Last, but not least, I now have the pleasure of pre-
senting to my readers

BECK'S NEW HISTOLOGICAL DISSECTING MICROSCOPE. 79

BECK'S NEW HISTOLOGICAL DISSECTING MICROSCOPE.

This instrument combines a compound microscope
with a single and dissecting one in a very compact and

practical form. The stout immovable arm carrying the
lens when used as a single microscope, is so arranged
that a compound body with eye-piece and draw lube may
be attached to its upper surface, whilst beneath it is

80 HOW TO SEE WITH THE MICROSCOPE.

fitted with the society screw, whereby an objective
ma}7 be used with it. The rack-and-pinion adjustment
work so smoothly that a one-fourth inch objective may
be focussed with exactness. The mirror beneath the
stage is so adjusted upon a swinging arm that it may
be turned up over the stage for the illumination of an
opaque object. A revolving diaphragm, with various
sized openings, is attached to the under side of the
stage. The outfit consists of a single lens of one-inch
focus for dissecting and botanical work, and an achro-
matic objective of one-fourth inch focus, the same as-
furnished with the economic microscopes, and one eye-
piece, giving a range of powers, with the draw tube,
of between 200 and 300 diameters, a pair of brass pliers,
two dissecting needles in ebony handles and a glass
plate with ledge. The whole packed in a neat mahog-
any case with lock. Several accessories are applicable
to this instrument.

THE NEW NATIONAL MICROSCOPE.

The stand which is fifteen inches in height, is con-
structed entirely of brass, of the highest finish and best
workmanship, having a broad, heavy tripod base. From
the centre of this base rises a stout column, to the top
of which is attached, by a firm joint, the Jackson model
arm, carrying the compound body, by which the inclin-
ation can be varied to any degree, from vertical to hori-
zontal, the whole instrument being perfectly steady and
free from tremor in any position. The very highest
powers may be used with it, as the body, being sup-

THE NEW NATIONAL MICROSCOPE. 83

ported by the arm throughout its entire length, cannot
have any unsteadiness or motion of its own.

The quick adjustment of focus is effected by means of
rack and pinion, with large milled heads, which works
so smoothly that there is no need to use the fine adjust-
ment for any power lower than one-quarter of an inch.
The latter adjustment is by means of a delicate micro-
meter screw and lever attachment, working with abso-
lute freedom from all motion, and by which the very
highest powers may be focused with the greatest exact-
ness.

The stage is of glass, with a complete rotation in the
optic axis, upon the top of which is a sliding object-
holder, very thin, and with a spring clip for holding the
object in place during rotation. This clip is removable,
in an instant, and the stage forceps can be inserted in its
place, thus allowing the latter to be moved about with
the object-carrier. Beneath the stage is a tube carrying
all the sub-stage apparatus, as the achromatic conden-
ser, Wenham's parabola, polarizing apparatus, etc., etc.
This is securely attached to the stage by a bayonet-
catch, and can be instantly detached, leaving a very
thin and unobstructed stage for oblique illumination.
The shutter diaphragm is of novel construction, with the
various-sized openings almost in contact with the
underside of the object under examination, a great
improvement upon the old revolving disk diaphragm.
A double mirror concave and plane is hung upon a
swinging bar, and with every possible motion for di-
rect and oblique illumination.

84 HOW TO SEE WITH THE MICROlsCOPE.

THE NEW ACME STAND.

During the session of the " congress" of microscop-
ists at Indianapolis in 1878, Mr. John W. Sidle, of
Philadelphia, and myself formed ourselves into a com-
mittee of two for the purpose of devising a new micro-
scope stand.

Mr. Sidle and myself were agreed in our opinions
that notwithstanding the recent improvements which
of late years had obtained, that there was still room
for further effort in the construction of microscopes.

Is was then and there proposed, deliberated on, and
agreed, that we would unite our energies in the en-
deavor to construct a microscope stand, which should
combine every possible good, be equal to any and all
work, exhibiting all the latest appliances, and withal,
to combine really reliable workmanship, at the lowest
possible cost, in fact at figures no higher than those
commanded by inferior instruments.

This arrangement contemplated that the author
should furnish all the suggestions which his long ex-
perience with the microscope might afford, while Mr.
Sidle was charged with the mechanical part in the con-
struction of the new stand.

This agreement has been carried out to the letter,
arid from the date named, until August last, Mr. Sidle
and myself have been in close correspondence, and for
the purpose named.

The first stand built under our compact was received
by me from Mr. Sidle early in August last, and as a

THE NEW ACME STAND. 85

matter of course, it got a pretty severe overhauling,
suffice it to say that I became so much pleased with oar
new bantem, that I gave it the name it bears, and have
no hesitancy in recommending this joint production of
Mr. Sidle and myself to my friends.

With this preliminary statement, I proceed to give
the reader a brief description of our new stand.

The Acme with closed tube, when in the vertical posi-
tion, is about fourteen inches in heighth, and its weight
about five pounds.

The foot is of cast-iron; "horseshoe" shaped and
similar to the Hartnack patterns, combining in the
smallest compass the necessary weight and accompany-
ing solidity. For real work in the laboratory this form
of foot is believed to be superior to all others. For
those who prefer the tripod model, Mr. Sidle will fur-
nish this form at the same cost, or in finished brass at
an additional cost of $3.50.

The entire instrument is supported by a heavy single
pillar of solid brass, the lower portion of which passes
through the cast-iron foot, the two parts being held
firmly together by a clamp-screw underneath the foot.
By virtue of this arrangement, the foot can be detached
almost instantly, or, by a half-turn of the lower clamp,
the foot can be reversed on the axis of the pillar, thus
ensuring the greatest stability when the stand is in the
horizontal position. The lower shoulder of the brass
pillar passing through the foot is accurately turned and
fitted, and when desired the moulding at the part of
the brass pillar immediately adjacent to the top of the

86 HOW TO SEE WITH THE MICROSCOPE.

foot can be divided to degrees for the measurement of
angular aperture, my own stand is thus arranged.

Besides those already mentioned other advantages
occur, from having the foot of the stand removable,
some of which may be enumerated as follows :

First, by detaching the base, the instrument can
easily be carried in the pocket; it is also much easier to
pack, and occupies much less space in the packing. It
can thus be carried from place to place even in the nar-
row accommodations afforded by a small valise, the
bother of lugging about the usual microscope case
being no longer necessary.

Second, Mr. Sidle provides at a small extra cost a
neat black walnut base board, furnished with small
lamp fitted with universal movements. This board has
also the necessary brass fittings to receive the pillar of
the microscope, which can be clamped to the board.
By this arrangement all that is necessary to convert the
instrument into a first-class hand microscope is to bring
the body to the horizontal position and to adjust the
object and the illumination.

With the stand as thus arranged I have repeatedly
exhibited objects illustrative of my lectures to the col-
lege class of 150 students, the instrument being passed
from hand to hand throughout the entire class, and re-
turned to me everything remaining in perfect order.

To teachers this feature of the stand will be of value.
It will also be found a great convenience at times when
the microscope is called on to furnish entertainment in

THE NEW ACME STAND. 87

the family circle, and objects can thus be exhibited
with great rapidity.

By means of a strong trunnion joint the body of the
instrument can be inclined at any desired position
between the vertical and horizontal, the requisite
stability of motion being secured by heavy " cheek-
blocks;" the joint has also compensation for wear.

All the working part of the Acme above the base are
of solid brass, bright finished, and nicely lacquered.

The main body-tube- is one and five-sixteenth inches
in diameter. This tube articulates with the limb by
means of heavy "T" guides or angle pieces, thus secur-
ing broad bearing surfaces and also perfect freedom
from lateral displacement. Mr. Sidle has put himself
to much trouble to perfect this portion of the stand.

The main-tube is five inches in length. This is sup-
plemented with a draw-tube, which can be drawn out
to the standard length of ten inches when desired.

The coarse adjustment is by rack and pinion. The
rack is well cut and durable, and the movement of the
tube by means of operating the large milled heads is
exceedingly smooth and entirely without "lost motion."

The fine adjustment is by a large milled head place
at the rear of the limb, and operating the main tube.
This milled head is one and one-fourth inches in diam-
eter, and is divided into twenty divisions. It acts
directly, i. e., without lever, on a micrometer screw
cut fifty threads to the inch, each division of the milled
head representing one one-thousandth of an inch. The
fine adjustment can therefore be easily made to answer

88 HOW TO SEE WITH THE MICROSCOPE.

the purpose of a micrometer for measuring small inter-
vals, or for the measurement of cover glasses, etc. In
this adjustment the same security against lateral dis-
placement is provided tor by means of the " T" angle-
pieces, as applied to the rack and pinion movement.

The lower end of main tube carries a nose-piece fitted
with the " society screw." This piece can, however, be
detached so that the bvoad-guage objectives now in pro-
of construction can be used on this instrument.

The main stage consists of a circular metal plate,
three and one-quarter inches in diameter, firmly bolted
to the heel of the limb, and in such a manner as to be
isolated from the movements of the sub-st'iye apparatus;
four holes are drilled through the main stage plate,
and so arranged that the spring clips may he adjusted
to hold the object-slide in either a vertical or horizon-
tal position. The spring clips may also be tiansferred
to the under surface of the stage, holding the object-
slide in contact therewith, when very oblique illumina-
tion is to be employed. The well-hole is of the usual
size and is provided with a standard screw-thread, by
means, of which the Woodward prism and other acces-
sory pieces can be readily placed in position. The stand
is thus fitted for such emergencies as required a fixed
and central sub-stage, separate from the movements of
the mirror ; the polariscope is also nicely provided for.

(NOTE.— It has lately come to the surface that, the diameter of the
** society screw " is not sufficiently large to meet the requirements of the
optician when low powers of the widest apertures are demanded. Mr.
Sidle is now making for the author a one-inch glass having a diameter of
over one inch, and the Acme has been designed to meet such requirements).

THE NEW ACME STAND. 89

The main stage has also conveniences for centering.
Furthermore, a solid plug is furnished which screws
into the well-hole, and forming when desired, a solid
stage. This plug has an "X" engraved thereon for
centering purposes.

The sub-stage proper, as well as the concave mirror,
are attached to a swinging bar by dove-tailed blocks,
The slides having compensation for wear, the sub-stage
can be centered. It is one and one-half inches in diam-
eter and is fitted to carry any of the accessory pieces
usually accompanying a first-class outfit. The sub-
stage and the mirror both slide with easy friction on
the swinging bar.

The swing-bar traverses the face of a circle of brass
placed at the rear of the stage, the centre of this circle
being in the plane of an object placed on the stage;
the centre of this circular plate is solid, that is to say,
it presents a solid core of about one inch diameter;
outside of this an angular groove is cut therein, in which
swings the heel of the swing bar, the method of at-
tachment of the swing bar to the circular plate giving
<>Teut solidity as wrell as firmness in motion. Thus it
will be seen that the " swinger" swings not on a centre
but around a centre. This part of the mechanism needs
only to be seen to be appreciated.

The mirror is of course removable, and a toy candle-
holder is provided to take its place for the measure-
ment of apertures.

A supplemental circular and revolving stage plate is
also furnished, which "slips" on and oft' instantly as

90 HOW TO SEE WITH THE MICROSCOPE.

may be* required. And by virtue of a nice little con-
trivance of Mr. Sidle's, the rotatory movement is very
smooth and nearly as central as would be expected from
stands of much higher cost.

When desired, Messrs. Sidle and Poulk furnish a
mechanical stage which slips on and oft* in place of the
rotary plate above mentioned; this mechanical stage
has vertical or horizontal motions to the extent ot
three-fourths of an inch. This, however, involves ar*
extra cost of $14.

To exhaust the list of American makers would be
quite beyond the province of this book. There remain
the names of Grunow, McAllister, Pike, Q,ueen,Schrauer,
Wales, George Wale, and others. Descriptions of the
stands supplied by these various makers have been
omitted, partially because the author unfortunately has
little acquaintance with their work, while that of oth-
ers which at times he has seen, seem practically to be
much the same as those already described, and the
reader would gain nothing by the repetition.

By way of concluding this chapter, and as supple-
mental to what has already been said as to the choice of
a stand, the writer would especially insist on the im-
portance of a stage thin enough to admit a beam of
light at 70°, from axis, not that the observer will
always work with oblique light, but, when occasion calls
fcr it, the stand should be capable of responding, and,
as has been before hinted, in these latter days these
kind of calls occur more frequently than was the case in
the days of }Tore. Let the novice especially, then, who

THE NEW ACME STAND. 91

proposes to purchase a stand that he will not feel com-
pelled to sell again in a few years, in order to procure-
a better one ; keep this point well in mind.

The author, too, unhesitatingly gives his support to
those stands having the swing stage and mirror; the
advantages accruing from this late improvement are
very valuable, of which we make particular mention of
one, to wit:

In former times, when sub-stages were practically a
fixture, it became necessary, in order to secure oblique-
light, to employ acchromatic condensers of wide aper-
tures and short focal distance ; the instrument was costly,
and necessitated the employment of accurate and expen-
sive sub-stage fittings, and, in general, could only be em-
ployed at a great sacrifice of pains, time and attention.
With the introduction of the swinging sub-stage and
mirror, all this is a thing of the past; the wide-angled
condenser is no longer necessary for the display of diffi-
cult structures ; on the other hand, it now seems desir-
able to employ condensers of the lowest angles, the-
required obliquity being obtained by swinging the sub-
stage, mirror and condensers to the proper angle. The
expensive centring apparatus not being required with
the low-angled condenser, their cost and bother are thus
avoided; at the same time better results are obtained,
and in a simpler and more convenient way.

There are other advantages, too, pertaining to the
use of the swinging stage and mirror, of which mention
will be made in the succeeding pages.

Finally, let me impress on the mind of the reader

"92 HOW TO SEE WITH THE MICROSCOPE.

that the large and expensive stands are not at all neces-
sary; the smaller and cheaper stands, if due care be
taken in the selection, will do any — practically all work
required in the progress of scientific investigation.
Furthermore, keep constantly in mind the fact that a
great deal of work, legitimately in the line of investi-
gation, can only be conveniently accomplished with the
small stands.

Where expense is no object, or even when one can
afford two stands without feeling thus crippled in other
directions, it will be found a luxury to have the two.
In the very nature of things, it is impossible to obtain
the firmness and solidity of a large and heavy instru-
ment through the medium of the smaller stands, and
occasionally this stability is a real convenience, resulting
in a saving of time and labor, as, for instance, in draw-
ing with the camera lucida. The graduated revolving
platform for the measurement of angles of aperture,
and similarly the circular graduated stage, with its
•centring adjustments, are handy things to have in the
house, but cost money, and, as a rule, can be dispensed
with.

And last — in this matter, far from being least — should
the res angusta domi pinch so bitterly as to compel you
for the time being to omit some necessary investment,
then I say, by all means make sure of the necessary ob-
ject glasses, quantity and quality included, and let the
stand "sweat" until the "good time coming" shall
enable you to provide a new and superior instrument.
Remember, too, that the finest and most expensive
stand extant, fitted to a poor objective, becomes not
only a dangerous tool, but also a positive nuisance.

CHAPTER II.

WHAT IS ANGULAR APERTURE.

During the lengthy controversy which occured be-
tween Mr. F. A. Wenham. optician to the firm of Ross
and Co., of London, and Mr. R. B. Tolles, of Boston,
Mass., the originator of the celebrated duplex object
glasses, the former presented ideas as to the functions
and nature of angular aperture which were not in strict
accordance with the popular views. Since then others
have done likewise, and it may be well enough to leave
the question open, without attempting to answer the
above interrogatory at all.

For the information of those, however, who are just
entering the study of microscopy, we will undertake to
tell what angular aperture was, or to be more definite,
what it was in 1856 ; and for this purpose, the author
selects the definition found in the Micrographic Diction-
ary by Messrs. Griffith and Henfrey, a work generally
acknowledged as authority in matters microscopical.

The angular aperture of an object-glass is the angle
measured by the arc of a circle, the centre of which is
formed by the focal point of the object-glass, the radii
being formed by the most extreme lateral rays which
the object-glass will admit.

Thus let L, in the left-hand figure 1 below, repre-
sent the lower portion of a microscope, objective, —

HOW TO SEE WITH THE MICROSCOPE.

a perpendicular section of the lowest combination of an
object glass of small aperture.

"a is the angle of aperture, and f e the most oblique
rays which the object-glass will admit. The angle is
measured by the dotted arc b in the object-glass of

larger aperture (Fig. to the right) ; the arc 6, which
measures the angle, is much larger, and the radii repre-
senting the extreme lateral rays are much more oblique.
Hence it is evident that the object-glass of larger aper-
ture admits all those rays admitted by that of less
aperture, and a certain number of other rays, these
being more oblique."

• The above definition has been and is now generally
accepted. Messrs. Griffiths & Henfrey proceed to give
their demonstrations of the effect of aperture, as thus
defined, in an interesting and lengthy article, one that
is well worth perusal by those desiring to know how
things stood twenty-two years ago. Our limited space
forbids its reproduction here.

HOW SHALL WE MEASURE ANGULAR APERTURE. 95

HOW SHALL WE MEASURE ANGULAR APERTURE.

While the nature and functions of angular aperture
remain a matter of controversy, this too may be allowed
to remain an open question . Recognizing, however,
the fact that object-glasses continue to be made and
sold, the makers claiming for them specific apertures,
we proceed to give the plan usually adopted by the
optician, and at the same time adapted to the use of
those working with the smaller class of stands.

It will be advantageous to the beginner to operate
either in a dark room or in the evening. Select a good
sized table, and on this, at the end nearest the operator,
pin down a large sheet of paper, say twenty inches
square. On this paper place the microscope, bring the
tube to a horizontal position, and screw on the object-
ive to be tested. Mark with a pencil certain points
along the base of the stand, so as to enable you to
describe a circle with pencil and dividers, in which the
base will just revolve without lateral play. Next,
provide a common candle, and, if necessary, cut this
down so that the height of the flame shall be level with
the objective in its horizontal position ; light the candle,
point the objective directly at the light, having pre-
viously removed all sub-stage incumbrances, crouching
down, and with the eye at the eye-piece, adjust the
direction of the instrument as nearly as possible to the
candle ; the field of view will of course be illuminated
from the radiant.

Now revolve the entire instrument, being careful to

96 HOW TO SEE WITH THE MICROSCOPE.

keep the base always within the circle drawn on the
paper, and continue the movement (either to the right
or left, as the case may be), until one-half of the field
shall be bisected — i. e., one-half bright and one-half in
the shade. Now select some straight portion of the
base, marking a straight line coincident therewith with
a pencil, or, placing a rule in contact with any two
salient angles of the base, draw a line.

Next, revolve the entire stand in the contrary direc-
tion, passing the candle, and until you again get a field
half bisected similarly, as before mentioned. Now
selecting the same side, or the same two salient corners
of the stand, mark another line.

These two lines will be found divergent with each
other, and with a parallel rule it will be found easy to
produce parallel lines which can be continued until
they meet ; this done, it only remains to measure the
angle obtained with a common protractor, or other in-
strument designed for the measurement of angles.

Where tolerable accuracy is important it will be well
to cross-question the result by repeating the operation.
There ought not to be a discrepancy of more than one-
half of one degree.

Those who possess the large stands fitted with gradu-
ated and revolving platform will of course avail them-
selves of the convenience ; the operation is practically
the same; thus, having bisected the field (say to the
right), read the angle, which will be indicated by a
mark on the platform adjacent to the graduations ; then
bisect the field to the left, read the angle again, sub-

OBJECT GLASSES. 97

tract one reading from the other, and the difference is
the angle of aperture.

There being no means for the actual determination of
the bisection of the fields, this having to be judged of
by estimation, follows that the plan is not rigidly
accurate; the author has, however, measured repeatedly
the same object-glass, following as above described, and
without a variation in the results of more than a half
degree; many of his pupils, too, on their very first
attempts, are quite as successful.

The bisection of the fields is much more easily arrived
at in the evening.

OBJECT-GLASSES.

Years ago wrote Dr. Carpenter thus:

" It may be safely affirmed that the most perfect
object-glass is that which combines all the preceding
attributes (viz., defining power, penetrating power, or
focal depth, resolving power, and flatness of field) in
the highest degree in which they are compatible one
with another. But, as has just been shown, two of the
most important — viz., penetrating power, and resolv-
ing power — stand in such opposite relations to the
angular aperture, that the highest degree of which each
is in itself capable can only be obtained by some sacrifice
of the other ; and therefore cf two objectives which are
respectively characterized by the predominance of those
opposite qualities, one or the other will be preferred by
the microscopist, according to the particular class of
researches he may be carrying on ; just as a man who is

7 Microscopy.

98 HOW TO SEE WITH THE MICROSCOPE.

about to purchase a horse will be guided in his choice
by the kind of work for which he destines the animal.
Hence it shows, in the author's estimation, just as
limited an appreciation of the practical applications of
the instrument, to estimate the merits of an object-
glass by its capability of showing certain lined or dotted
tests, without any reference to its penetrating power or
defining power, as it would be to estimate the merits of
a horse merely by the number of seconds within which
he could run a mile, or by the number of pounds he
could draw; without any reference, in the first case,
either to the weight he could carry, or the length of
time during which he could maintain his speed, and, in
the second case, either to the rate of his draught or his
power of continuing the exertion. The greatest capac-
ity for speed alone, the power of sustaining it not being
required, and burden being reduced almost to nothing,
is that which is sought in the racer; the greatest
power of steady draught, the rate of movement being of
comparatively little importance, is that which is most
valued in the cart-horse;, but for the ordinary carriage-
horse or roadster, the highest merit lies in such a combi-
nation of. speed and power with endurance as cannot
coexist with the greatest perfection in either of the first
two. The author feels it the more important that he
should express himself clearly and strongly on this sub-
ject, as there is a great tendency at present, both among
amateur microscopists and among opticians, to look at
the attainment of that resolving power which is given
by angular aperture as the one thing needful. . . .

OBJECT GLASSES. 99

It is neither the only nor yet the chief work of the
microscope (as some appear to suppose.) to resolve the
markings of the siliceous valves of the diatomacea ; in
fact the interest which attaches to observations of this
classier se, is of an extremely limited range. . . .
And the more carefully we look into the history of
those contributions to our knowledge which have done
the most to establish the value of the microscope as an
instrument of scientific research, the more clear does it
become that for almost every purpose except the resolu-
tion of the diatom tests, objectives of moderate angular
aperture are to be decidedly preferred." *

This quotation — essentially true when first published
— has been, and to a considerable extent now is, the
orthodox faith ot the microscopist. It has been en-
dorsed by everybody, both at home and abroad; the
world of observers have rested peacefully at ease on its
broad platform; the man of science was serene and
content with his medium apertures; but it was the
crowning glory of the quack that a " good hcnest,"
low-angled, " working" triplet cost only a dollar or
two. A.nd it was a fact, that so far as faith was con-
cerned, the scientist and the veriest quack were in the
same boat together, and both found pleasure in endors-
ing the teachings of Dr. Carpenter.

It seems to me that this singular state of things can
be easily accounted for. The hard-working investiga-
tors had little opportunity to study object-glasses, their
time being completely occupied, and their eyes sorely

*"The Microscope and It, Revelations" fifth edition, 18Y5, page 204.

100 HOW TO SEE WITH THE MICROSCOPE.

taxed in the daily routine of labor and study. Their
glasses were the best that could be procured when pur-
chased, and, as far as their personal experience with
them could attest, their experience was in harmony
with the laws laid down by Dr. Carpenter; and they
had rt no time to waste" in fussing over " diatom tests,"
etc.

On the other hand, the empiric replies, " Your high-
angled glasses are all well enough for the diatom man,
but for my work give me reliable French triplets of
moderate apertures;" and in this statement the author
is in entire and perfect harmony !

The author repeats, that ten years ago the doctrines
taught, as contained in the previous quotation of Dr.
Carpenter, were essentially true; he has 110 fault to
find with their original publication, but he does regret
that Dr. Carpenter has allowed them to retain their
place, unchanged or unre vised, in his late editions.

Let us glance for a moment at the history of the ob-
ject-glass as connected with its aperture. Years since
it was known that the .exhibition of surface-markings
required to a greater or leeser extent the employment
of lateral or oblique light; width of aperture hence
became a desideratum, at least in such glasses as were
to be used with this object in view.

Whether right or wrong, demands were made on the
optician for objectives possessing increased apertures.
Notably, this demand was first met successfully by our
own countryman , the veteran Charles A. Spencer;, who
produced a glass of wider angle than had been pre-

OBJECT GLASSES. 101

viously accomplished and thereby astonishing the world,
sorely punching the English opticians (who flattered
themselves on secure ground at the head of the profes-
sion) with an exceedingly sharp stick; with this glass
Mr. Spencer succeeded in displaying both sets of lines
on the diatom, now known as Navicula Spencerii.

The London makers followed suit, giving especial at-
tention to the extension of aperture, and, as might be
reasonably expected, the problem was to get light of
extreme obliquity somehow through the lens, nor were
they (the makers) very particular to stand on the order
of its going; hence it came about that very many
glasses were made and sold having increased angle, by
virtue of which they were able to display certain ac-
knowledged difficult tests ; but, on the other hand, the
lateral pencils being poorly corrected (if corrected at
all), these glasses could not compete by centrally dis-
posed light with the well-corrected but narrow angles
previously in use.

It was, therefore, to the wide-angled glasses of that
day that Dr. Carpenter's remarks had force, the highest
possible angle attainable being then limited by popular
opinion to Ib5°. What is now known and recognized
as a high-angled glass of 175° was then not only
unknown, but would have been deemed a sheer im-
possibility, and it therefore becomes obvious that any
remarks at the time referred to, whether by Dr. Car-
penter or by other authors, cannot be applied consist-
ently to the wide-angled glasses of the present date.

Tliose were the days, too, when the resolution of the

102 HOW TO SEE WITH THE MICROSCOPE.

nineteenth band of the Nobert test-plate was said " to
be a matter of faith rather than of sight." The curious
reader is informed that the original of the quotation
will not be found in the last edition of the ' ' Microscope
and its Revelations ! "

Again, the high-angled objective, as at present con-
structed, is an entirely different affair from that of
former times. In place of achromatism, then thought
to be the ultima thule of perfection, the finest glasses
now made can hardly be said to be achromatic. And
then, again, the immersion system has been adopted
with its manifold advantages. Improvement upon im-
provement has almost marked the rolling months of
the calendar, while each succeeding year, to the number
of ten or more, has been richly laden with the fruits of
the optician.

In this wonderful march of progress, our own coun-
try, I am proud to say, has ever been at the front, and
with colors flying. As before stated, Spencer, with his
resolution of the navicula, commenced this march of
progress, and slackened not the pace until the reputa-
tion of American objectives were duly acknowledged
abroad. Then, indeed, he retired for a time, resting
gracefully on his well- won laurels; and now appears
Tolles at the van, who with almost superhuman genius
and energy grapples with the very laws of optics, and
bends them to his inflexible will !

Notwithstanding that the reputation of the country
was quite safe in the hands of Mr. Tolles; Spencer,
after a year or two of rest, again comes forward, assisted

OBJECT GLASSES. 103

by his two sons, both of them, as a matter of course,
" to the manner born," and in the very prime of life
and activity.

Thus far I have simply referred to Spencer and
Tolles, because they have contributed largely to the
production of high-angled objectives; but the list of
American opticians is not thus complete; we have
Wales, Zentmayer, Gundlach, and Grrunow yet in
reserve, whose productions in their several lines are
not inferior to any imported.

In the foregoing brief and general history of the
American wide-angled objective, the conclusion is in-
evitable, first, that during the past ten years something
has been accomplished, and that in the interim our
opticians have not been idle ; secondly, that the modern
high angled glass is to be judged of strictly on its merits,
and not by what was affirmed of a medium aperture ten
long years ago.

The converse of this is equally true, and the author,
in presenting his views of to-day, declines to be held
responsible for what the future may bring forth.

In this place it may be well to consider what, in
common parlance, constitutes a high-angled glass. The
writer has already in print stated his individual views
which have since undergone no change. As a rule, refer-
ence being made to wide apertures, most persons are
prepared for some great show of figures, such as "175°"
or "179°"; others might call for nearly "180°"; and
then again, others there are who would insist on pass-
ing the " impossible" 180° corner, and revel among the

104 HOW TO SEK WITH THE MICROSCOPE.

balsam angles to the tune' of 100°, or even higher.
In dealing with objectives of short focal distance, all
this may be well enough; the writer, however, prefers
to regard as high-angled, any, and all glasses, without
reference to their focal lengths, which are endowed
with the widest apertures obtainable. If this platform
be accepted, then it will occur that a one-inch of 50°
should be classed as a high-angled objective, and simi-
larly, a two-inch of 25°. And, again, it would also then
occur that a one-sixth of 130°, which fifteen years ago
ranked as a wide, would now be classed as a glass of
medium aperture. And furthermore it may possibly
(yea probably) have place, that there are many observers
to-day, loud in their denunciations of the "wide-angles,"
falling back on "The Microscope and its Revelations"
for authority, who, in their habitual use of what are
now known as medium apertures, are in truth the real
culprits, to whom and for whom were Dr. Carpenter's
original remarks intended.

As has been suggested on a previous page, there may
be seriously some question, not only as to angular aper-
ture per se, but as to what constitutes the measure of
the same. It is one thing to get light through an ob-
jective, and quite another to bring said light into the
traces, and render it of use to the observer. There are,
too, scores of high-angled glasses (so-called) sold as
having angle of 175°, and possibly more, that are
entirely worthless when worked with pencils beyond
130° ; indeed, many that I have seen would utterly fail
when compared with a really good glass of 115°.

OBJECT GLASSES. 105

The writer has before him a glass of the latter angle,
(115°,) made by C. A. Spencer & Sons. It is what
they call one of their " professional series" — a dry one-
fourth ; the makers ought not to expect that this glass
should be called on for work requiring oblique pencils
greater than 100°.

Now this glass — this professional one-fourth — will
give me real good shows, even when worked at all the
obliquity obtainable on my Zentmayer stand ; and thus
have I seen with it the longitudinal markings on the
balsamed surriella of the Moller test-plate, and this is a
test that will defeat many dry eighths, engraved by
their makers as having 160° or more angle.

From this little experiment — one that the writer has
repeated scores of times in the interests of his friends —
some curious conclusions might be arrived at, which,
although possibly coherent and plausible in detail,
become absurd when considered collectively; thus it
might be held :

First. That both glasses having at least 160° of aper-
ture, are in fact high-angled glasses.

Second. That of the two named, the Spencer is the
better glass.

Third. That the Spencer objective has really but
an angle of 115°, as marked by its maker; that its capa-
bility of admitting working beams up to 140° gives it
no real claim to those figures.

Fourth. That, as any good eighth of 140° will
easily show the longitudinal markings of the surriella,
it is proven that the one referred to has not that angle

I
106 HOW TO SEE WITH THE MICROSCOPE.

at all, and is, in fact, but a medium power glass — the
general verdict being that it is an indifferent one at the
best.

Fifth. That the capacity of an objective to display
markings on balsamed and difficult tests, at or near the
limits of its aperture, is no index of angular aperture.
In the case presented, if it so be that the eighth, when
worked at 140°, gave fair and distinct images of the sur-
riella, then there is no reason to dispute the angle as
claimed for the glass ; let the experiment be repeated
an using angle of 120°, and over dry as well as bal-
samed mounts.

The above may be taken as representing individual
differences of opinion. Either of the conclusions pre-
sented have been urged on our attention time and time
again. To the second, third, and fourth, the author gives
his assent, and has never allowed an opportunity to pass
without exposing by actual demonstration the fallacy
contained in the fifth.

From the preceding, then, it becomes apparent that
there is much difference of opinion as to what consti-
tutes angular aperture or the measurement thereof.
Until there can be some more precise plan arrived aty
let the purchaser of any objective imperatively demand :

First. That the objective, in general, work with its
full vim fully up to the limits of the aperture claimed
for it; that the images be strong, vigorous, brilliant,
and without distortion, and that such images shall not
be surpassed in any particular by any similar glass,
without reference to its angle. If it be that you have

OBJECT GLASSES. 107

a wide aperture in hand, see that its work by central or
centrally disposed light is not excelled by any objective
of narrow angle extant. In calling on the glass at the
limits of its aperture, demand, and see to it particularly,
that there be no letting down of general performance,,
that the images remain strong and vigorous, that the
corrections are not impaired, and even with the widest
apertured objective known, that there be no sensible
distortion of the image.

Again, if it so be that you desire thus to test an ob-
jective claiming considerable aperture, say 170° or 175°y
and adjustable, note whether there be any special ad-
justment required when worked at or near the limits of
its aperture, other than necessary for its correct per-
formance by central light; if this be found the case,
the indications are that the two sets of pencils are not
in harmony with each other — as the Germans say, are
not " married." It will be necessary to use a little
discretion here, for some of the very finest glasses re-
quire a slight change of adjustment under the condi-
tions named. The less of this especial adjustment,
however, the better.

Any objective that will stand acceptably the fore-
going- tests may be allowed to ' ' pass muster " as to its
aperture sans peur et sans reproclie.

In the act of writing the above, the author was inter-
rupted by a friend with the remark, " Are you not
screwing things down pretty fine? Don't you see that
your method not only is a severe test as to working

108 HOW TO SEE WITH THE MICROSCOPE.

angle, but is also a severe test as to the general quali-
ties of an objective?"

In response to this interrogatory, I reply, that it's
high time things were " screwed down." As to the
latter portion of the remark of my friend, it may be
observed that the directions given indicate a part, and
part only, of the course to be pursued in testing the
performance of a really first-class American objective
of wide aperture.

The plan proposed is liable to another, and, in the
minds of some, a most serious objection; says one,
" Don't you see that you have advanced no positive
guage? Your idea simply is to compare one glass with
.another — in short, it means 'fighting objectives"
Selah!

SOMETHING FURTHER ABOUT OBJECTIVES.

There is another matter of common acceptance which
has in the past made some mischief; I refer to the fact
that the focal or working distance of an objective has
been and is considered the index of its capacity for cer-
tain classes of work. Thus, the incli has been set apart
for the study of such objects as required examination,
with powers from 50 to 150 diameters, and where its
comparatively long working distance was desirable,
while the one-fiftieth, whose lowest power of 2,500
diameters and its exceedingly short working distance,
•could not perform the work of the inch — the one-
fiftieth being reserved for the investigation of the most
minute organisms, and under the highest amplifications.

SOMETHING FURTHER ABOUT OBJECTIVES. 10(J

Now, in the instance cited the popular idea is correct.
The inch cannot do the work of the fiftieth, nor can the
fiftieth do the work of the inch, and each, as to the
other, are to be appropriately brought into use.

But, as is well-known, between and intermediate to-
the scope of the two glasses named, there are several
objectives having not only intermediate but variable
focal lengths. Among these latter, too, are to be
found the objectives known as " medium powers," and
it is with reference to these that it may be affirmed that
the broad rule governing the inch and the fiftieth does
not hold good.

Some four or five years since, the author, in writing
to a brother microscopist, hazarded the statement that
the time would surely come when the optician would
furnish one-sixths, capable of performing all the work
then done with the one-fiftieth. The principal reason
advanced at that date, in support of his opinion, was,.

First, assuming the case of a perfect objective with a
perfect eye-piece, he claimed that it made no difference
to which end of the tube the power should be applied.

Second, the nearer perfection arrived at in the con-
struction of the objective and eye-piece, the higher may
be the power of the latter ; and

Third, as we have no right to expect absolute per-
fection in the construction of objectives, it nevertheless
seemed reasonable to infer that the optician could bet-
ter handle and adjust a lens of sensible dimensions,
such as are used in the manufacture of the medium

110 HOW TO SEE WITH THE MICROSCOPE.

powers, than could be possible with the merest speck
of glass forming the fronts of the one-fiftieth.

Whether the ideas thus advanced were correct or not,
the fact is patent that in less than two years from the
-date of the said letter, Mr. Tolles produced a one-sixth,
that excelled for any and all work the performance of
any one-fiftieth on record. This one-sixth is still in
the possession of the author, who, ere the glass was
thirty days old, pitted it against the finest fiftieth to be
found in the country. The battle waged for an entire
week, but the result was decisive. It was David vs.
Goliath, and David had the best of it.

Scarcely had another month elapsed before Mr. Tolles
again sent the writer another glass — this time a tenth
— which, in turn, eclipsed the previous inimitable work
of the sixth; while at a still later day, Mr. Herbert
Spencer produces a tenth, made on a somewhat differ-
ent formula, the performance of which is not excelled
by any glass yet made, " be it a fifth or a fiftieth."

Without reference to the " impossible 180°," it may
be positively claimed .that either of three glasses named
have greater aperture than is possible (or has thus far
been possible) to obtain with the fiftieths.

As has already been stated in the introduction, the
writer was the first to call public attention to the claims
of American objectives of medium power. Statements
so radically at war with the generally accepted popular
belief were destined, as a matter of course, to meet with
opposition. Microscopists from almost every section
came in person to see for themselves, many of them

SOMETHING FURTHER ABOUT OBJECTIVES. 11]

bringing their favorite high-power glasses for compari-
son, and returning to their homes satisfied with the
trip, leaving the one-sixth and the tenth to encounter
the next comer.

It being probable that there are others who yet re-
main to be convinced as to the accurary or validity of
the claims of the " medium powers," it may be stated
that at this late day the writer is no longer in a minor-
ity of one. Microscopists of note have studied the
situation, arriving at similar results. About twelve
months ago, Mr. John Mayall, Jr., a well-known and
talented microscopist of London, wrote as follows:

" I am not going to enter into a mass of details of
the various trials I have made with Tolles' one-fourth
and one-eighth. Suffice it to say that no lenses that
have been in my hands have ever been so thoroughly
tested against the best lenses by English, French, and
German opticians (here Mr. Mayall presents a list of
seventeen recent immersion objectives by the most re-
nowned makers in Europe) ; and without reserve of
any kind, I say these lenses are the finest I have ever
seen. I affirm, then, that with cen-

tral and oblique light on all the objects that are known
here as tests, Tolles carried the palm. I find, on the
most severe tests, there is in Tolles' lenses a better cor-
rection for spherical aberration, the image is more crisp
and clear. By difficult tests, I mean, for instance, sur-
rirella gemma with central light, or amphipleura pellu-
vida with oblique light. I urge that

low-angle lenses will not exhibit the definition these

112 HOW TO SEE WITH THE MICROSCOPE.

lenses will show, and that if one takes a higher power
that will show the images, he will find, by comparison,
the higher power will be the more difficult to manage.
The whole question turns upon results; if you are con-
tent with medium images, use medium or low-angle
objectives ; if you train your eye for fine images, you
must use high-angled objectives."

In 1876, Dr. J. Gr. Hunt, of Philadelphia, a widely
known and expert microscopist, after having given the
new American objectives of medium power close study,
writes as follows ; and believing that the doctor's letter
will be found of general interest, we give it entire*
The glass he makes reference to was a Tolles tenth:

" I can now report to you that the one-tenth you
sent me is grand. It contains more good qualities than
are to be found in many first-class lenses — perfect
mechanical workmanship, large field, gives sharp image
on the margin of field, decision of definition leaving
nothing doubtful or foggy, equal penetration with reso-
lution; thus being superior for histological work.

I could engrave it all over with marks of
admiration. . . . For the best work of
the botanist or histologist it has a definition which can
be retailed, with an amplification such as I have not
seen in any one twenty-fifth or one-fiftieth that has come
under my notice. ... I see in its con-
struction more finger skill, more time and conscious
brain patience than mathematics. Hence its charac-
ter; it has no precedent, but is wholly original, and
unlike any other make, English or continental."

SOMETHING FURTHER ABOUT OBJECTIVES. 113

The preceding quotations are thus presented to the
reader because the issue we have under consideration is
therein discussed typically (I may say) from both the
American and English standpoints. To the testimony
cf these talented gentlemen the author could, did his
space allow, add a mass of similar evidence.

I repeat it is not consistent with the limits of this
little book to further discuss the issue in question. The
author therefore dogmatically asserts that his positions
taken in public print relative to the matter we have
been considering, were then correct, and have so re-
mained up to the present date.

But mark this point: the claim thus established in
favor of i4 medium powers" of the widest apertures
has no reference whatever to hosts of objectives made
and sold with high-sounding figures attached. Keep
this fact in lively remembrance.

We are now prepared to return directly to the point
from which we started. We have seen by our digres-
sion that the relations existing between the inch and
the one-fiftieth are to be essentially modified, relatively,
as to the nature and performance of a one-sixth as
compared with that of a one-fiftieth. For instance, if
it were true, as has formerly been accepted, that it is
the province of the inch to assist in the study of the
simpler organisms, and that of the fiftieth for the in-
vestigation of the most delicate structures, it does not
hold good at this present writing that a one-sixth or
tenth (generally classed as medium powers) are the
proper objectives for an intermediate class of work only.

8 Microscopy.

114 HOW TO SEE WITH THE MICROSCOPE.

It is obvious also that, if the one-sixth and the one-
tenth are more than capable of doing the wrork formerly
set apart for the employment of the one-fiftieth, the
former have the better right to be regarded as "high
powers."

Furthermore it occurs in the present advanced stage
of optical science that it is really quite impossible to
precisely define what constitutes a "medium power"
glass, or for what particular class of work would such
glasses (if defined) be characteristically adapted. The
author confidently believes that still further and greater
improvements in American objectives are yet to be ac-
complished. He believes, too, confidently that, as the
instrument shall approach perfection, and still higher
eye-pieces be brought into requisition, he may yet live
to see the Nobert nineteenth band with a half-inch ob-
jective and a one-sixteenth eye-piece. It therefore
seems to him that any discussion as to the characteristic
duties of an object-glass based entirely on the focal
length of the same may wisely be dismissed as being
(for the present at least) impractical, if not impossible.

And now for some remarks that are not only possible,
but can, if the reader elects, be made eminently practical,
closely related, too, to what has just been written; and
in these the author hopes to render some service at
least to a portion of his readers.

A fine objective is in its very nature a costly instru-
ment, while on the other hand, it often happens that
the true lover of nature has unfortunately a light purse.
In fact, this whole situation is to be regretted, and cer-

SOMETHING FURTHEll ABOUT OBJECTIVES. 115

tainly to be ameliorated if possible. It happens, too,
that the so-called " high powers," such as one-twenty-
fifths, one-fiftieths, and one seventy-fifths, cost in them-
selves more than the majority of observers could afford
to pay for an entire outfit, and thus have been accessi-
ble to only a favored few. The price of the fiftieth, as
furnished by eminent makers may be quoted at from
$250 to $300. I dare say that more than one of my
readers, earnest workers with the microscope have
yearned time and time again, as they have read of some
wonderful things accomplished with a twenty-filth or
one-fiftieth, for the means to enable them to pursue
similar investigations. Let all such hail with joy the
announcement that these costly glasses are no longer a
necessity, and that their work can be not only done,
but better and with greater ease accomplished, with
what are known as medium-power glasses of wide
apertures; that there is no longer, too, any necessity
of going abroad, or paying duties thereby; that a one-
sixth, or, at the furthest, a one-tenth, costing from $60
to $85, will (if properly selected) compete in perform-
ance with any one-fiftieth extant — a fact, reader, worth
knowing.

Another dogma in the popular mind has very general
acceptance — to wit : that angular aperture can only be
obtained at the sacrifice of working distance. The old
saying is, that " it's a poor rule that won't work both
ways;" hence it should obtain conversely, that with the
sacrifice of working distance, angular aperture ought to
be obtained; but this is not always the case. For in-

116 HOW TO SEE WITH THE MICROSCOPE.

stance, one -sixth are now made writh apertures we will
say (to keep out of controversy) up to 180°, and with a
working distance of one-fiftieth of an inch. Now the
widest angled one-fiftieth in existence, with a working
distance le^s than half that of the one-sixth, will be
found to measure less than 170°, and in the latter glass
it is evident that, working distance has been sacrificed
without corresponding increase of angular aperture. The
case cited is an instance notably in point, and one that
cannot be dodged, and yet to a certain extent the same
will apply to some of the intermediate objectives.
Take again the before-mentioned sixth of the widest
angle known, and its working distance of one-fiftieth of
an inch. It will be found that, although it is possible
to obtain the same aperture for the1 tenth, the working
distance will suffer decrease ; and here again is another
instance where sacrifice of working distance is not
accompanied by corresponding increase of aperture.

The subject is by no means exhausted, and is well
worth a little ventilation. We can better get at the
situation by supposing a case which might possibly
occur in practice. Suppose then, reader, that you
desire five one-inch glasses, each glass to have a work-
ing distance of five-tenths of an inch, and each to mag-
nify with the two-inch ("A") eye-piece, fifty diameters,
and that you gave these five glasses respectively to five
opticians, to be made as per the conditions named.
Now, it will most probably occur that when you get
these five glasses in hand, the working distance and the
magnifying powers of each are true to the specifications,

SOMLTII1NG FURTHER ABOUT OBJECTIVES. 117

and further, that no two of the five glasses will have
the same angular aperture.

It's well enough to pause here and allow the approach
of a deluge of threadbare argument. Says one, "All
this proves nothing. It's quite possible that the glass
with the narrowest aperture may be the better corrected.
Let your own rule be here applied, and the quality of
the apertures tested; nothing short of a competitive
examination can be determinate."

To this the writer says amen ; but the reader is again
reminded that this is nothing more or less than "fi^ht-

o o

ing objectives." This is the course, too, which the
author has pursued in the way of making competitive
examinations of objectives in his own interests, and in
behalt of those of his pupils, his friends, and his corre-
spondents. The result being, in nineteen cases out of
twenty, that the glass with the wider aperture proved in
every other respect the better glass — a result, too, not
improbable in its nature, when it is borne in mind that
those of our opticians who have given great attention to
the development of aperture are no ways behind-hand
in their general professional attainments.

Again, (to steer clear of cavil or controversy,) suppose
that of the five glasses before named, all having the
.same working distance and amplification, the one with
the lower aperture being made by Mr. X., and the other
of wider angle being by Mr. Y., both objectives being,
too, equally well corrected. That such a condition of
things is ^)ossible no one will attempt to deny. Here
is A condition to which the popular dogma can be

118 HOW TO SEE WITH THE MICKOSCOPE.

applied to advantage — to wit: we can send to Mr. Y.
for another inch similar to the one in hand, but with a
lower aperture, and corresponding to that of Mr. X.,
and it will obtain that Mr. Y., in cutting down the
aperture of his inch to that of Mr. X., will increase his
working distance; and here (comparatively) we gain
working distance without loss, or, as it has been termed,
sacrifice of angular aperture.

Hence we arrive at the conclusion that the function
recognized as "angular aperture " per se is not a fixed
and definite quantity nor one that can be fenced in and
subjected to any fixed rules. Nothing definite in the
way of rigid law can be applied to it. In the case just
mentioned, another curious conclusion might be arrived
at, and justly too. For instance, the decrease of aper-
ture from that of the wider aperture to that of the lower
would not only be accompanied (accepting the popular
dogma), which in the case in question would hold true
by an increase in the working distance, but the penetra-
ting power of the glass would thereby be enhanced, and
this, too (comparatively), without loss of angle.

The facts presented are valuable, are significant, and
worth careful thought and study. The author has
never seen them in print, and they are, a's suggested,
the result of an active experience.

And this brings us to the consideration of another
matter; I refer to the popular dogma of "penetration."
This has been the biggest toad in the puddle, and has
exercised an active agency in roiling and mystifying the
mind of the microscopist. The doctrine of penetration

SOMETHING FUUT1IEK ABOUT OBJECTIVES. 119

as generally taken and accepted may be thus stated:
objectives of low angular aperture are endowed with a
peculiar inherent and intrinsic power, by virtue of
which they enable the observer to see and study struc-
tures situated in different planes of the object. For
example, if the objective be focussed accurately to
details occupying an intermediate plane of the object to
be examined, then will the low-angled glass allow the
observer, without change of focus, to study other
details of the said object, situated in planes either
nearer or more remote. We have been taught that this
is a most valuable property, and one due to the employ-
ment of low angles only — the idea thus conveyed being
that the low angles possess a peculiar and accommodat-
ing power of great value to the microscopist, to which
the wide apertures stand inflexibly opposed, and defiant.
In support of the doctrine of penetration , it has been
customary to present the case of the optical principles
governing the action of low apertures, contrasting the
same relatively with similar conditions involved in the
use of the high angles ; thus we have been taught that
the narrow-angled glass admits as a matter of course,
but a narrow cone of light, the pencils crossing at the
focal point at a very acute angle. Hence it is "obvious"
that it matters not whether the object to be viewed be
placed exactly at the crossing point or a little within or
without the said focus. The accompanying and sup-
posed increase of working distance attributable to the
narrow aperture of course is not lost sight of; and we
are here admonished to keep in mind the fact that, with

120 HOW TO SEE WITH THE MICROSCOPE.

an infinite working distance, there would be no need of
special focal adjustment, and hence the longer the work-
ing distance the better. On the other hand, we are
told that objectives with very high apertures admit a
much wider cone of light, the lateral rays of which cross
in the focal point, at a more obtuse angle, and hence
the necessity of placing the object to be viewed exactly
in the focal plane. On all other planes, nearer or more
remote, the object being out of the crossing of the rays,
cannot be well defined; and here again, conversely the
presumed decrease of the working distance due to the
increase of aperture is held prominently in view.

To all of the above, which has proved so acceptable
to the world of microscopists, the author long ago pub-
lished his dissent. He never did, and does not to-day,
take the least stocK. in the aforesaid enunciation of the
so-called doctrine of penetration.

Admitting, as in the case of the two objectives pre-
sented, that the cone ot light illuminating the field
from the high-angled objective is wider, and that the
lateral pencils cross in. the focal point at a more obtuse
angle than can occur in the case of the narrow-angled
glass, it is nevertheless true (and singularly this little
fact seems to have been entirely lost sight of), that the
wider cone of light due to the employment of the wide
aperture includes all of the central pencils present in the
case of the narrow-angled glass. In other words, there
are just as many central pencils at work (and remember
that these are the fellows that cross the focal plane at
such an acute angle, thus furnishing the beloved pene-

SOMETHING FURTHER ABOUT OBJECTIVES. 121

tration) in the making up of the wider cone as can
occur with the use of the narrow aperture ; furthermore,
that it would be not only possible, but eminently prac-
ticable, by the use of a diaphragm, to cut down the
cone of the wider aperture objective to correspond with
that of the low-angled glass ; hence it is obvious that in
this latter case the two objectives would be worked
under similar conditions as respects the angle at the
crossing of the rays, and, applying the argument
based thereon, neither glass can be endowed with the
greater penetration.

Says one, "How about the working- distance?"
The relations of angular aperture to working dis-
tance have already been discussed, and intentionally,
with the view of preparing the mind of the reader for
the above interrogatory. But there remain other con-
siderations bearing on the matter of working distance,
and the clinching- argument on the part of the writer
remains to be presented.

In doing this, the author is compelled to deal in
assertions dogmatically. In the handling and compar-
ing of object-glasses, he has had a very large experience,
and he feels that he has the same liberty to speak! ex
cathedra as has been granted to others. Moreover,
what he now has to say is " important if true," and he
is as well assured ot their correctness as of any other
fact within his knowledge and experience, nor is he
alone in the matter about to be stated. Without
•exception, all who have experimented in the proper
direction assent to all that will be here claimed, while

122 HOW TO SEE WITH THE MICROSCOPE.

those who have not, may reasonably be expected to
know not.

Let it be required to display an object under the
microscope, and under a given amplification. It
matters not what the object may be — be it a diatom, or
a bit of voluntary muscle, or what not; nor dees it
matter as to the amplification — be it 60, 600, or 6000
diameters, as the case may be.

Now, to attack this object, we will provide two sets-
of objectives, including all the focal lengths, say from
the inch, upwards, to the one-fiftieth — these glasses to-
be the very finest of their kind made at the present day,
and notably of low apertures ; the other set to be simi-
lar as to the range of focal length and quality, but
ciotably to possess the highest apertures (respectively)
known.

Now choose your object, select your amplification,,
and display the former, using the low angles with their
very best foot foremost. This done, allow me to
remove the objective, replacing in its stead the suitable
high-angled glass, and I affirm pointedly that the object
shall be equally well displayed, under the same amplifi-
cation, etc., and by an objective, too, having greater
working distance than the low angle first selected.

It should be contemplated, in any competitive com-
parisons of this kind, that they be conducted without
prejudice, and solely in the interests of science, and
when so conducted, and by observers fitted for the
emergency, the author apprehends that his statements
will be found correct.

BALSAM APERTURES.

We have thus again endeavored to make manifest
that the idea that angular aperture is accompanied by a
sacrifice of working distance has no real existence —
that is, in the form popularly accepted.

Thus far we have discussed "angular aperture" in it&
popular signification, and, in several of its aspects,,
from the definition given from the micrographic dic-
tionary. Taken in conjunction with the remarks we-
have thus far had occasion to offer, the reader would
probably infer as axiomatic that the range of apertures
would necessarily be confined within the axial pencil
and the one striking the underside of the slide at near
coincidence, thus traversing and limited by an aro
measured by nearly 90° — the latter being equal to 180°
of aperture. This, too, is the precise aspect to which
the author desired to restrict his observations. Now
there is another kind of aperture of which very littla
is generally known, we refer to

BALSAM APERTURES.

From a theoretical or mathematical standpoint, the
study of balsam angles fairly bristles with difficulties;
it has been to us a problem to which our school boy
wrestlings with Euclid seem a pleasant and simple exer-
cise. While we frankly admit our incompetency to
properly present the subject, we have to remark, on
the other hand that we were not willing to send forth
this little book without at least some mention of the
matter.

Observers interested in the history of the American

124 HOW TO SEE WITH THE MICROSCOPE.

objective (and American observers ought to be, to a
man) will find the subject ably discussed in the columns
of the London Microscopical Journal, reference being
made to the celebrated controversy on the subject of
angular aperture between Mr. R. B. Tolles, of Boston,
Mass., and Mr. Wenham of London. In this discus-
sion, the American side of the question was ably assisted
by Col. J. J. Woodward, of the U. S. Army, and Prof.
Keith, of Georgetown, D. C. The entire controversy
is well worth reprinting in a consolidated form, and
should find an appropriate place in the library of every
American observer.

No attempt will, tor the reasons given, be made to
discuss the subject of balsam apertures in these pages.
We shall, however, try and give the novice an idea or
two connected with balsam angles without which some
things which will hereafter be presented, would be
wholly unintelligible.

Suppose we put a ray of light down the tube of the
microscope, thus reversing the usual order of things,
and that said pencil have an angle of 41°. This pencil
traversing a suitable objective in position over a bal-
samecl mount, will find emergence into air at 90° ; equal
to what is recognized as 180° of aperture. Such an
objective would be said to possess a balsam angle of 82°,
in other words (rejecting fractions), the balsam angle
of 82° is said to equal an air angle of 180°.

Now it is claimed by certain American opticians, that
it is possible to construct immersion lenses that are
capable, when worked over balsam mounts, of recogniz-

BALSAM APERTURES. 125

\u<r interior pencils greater than 41°. Mr. Tolles claims
for some of his recent immersion objectives, balsam
angles as high as 120°.* We have devoted a great deal
of time to the study of this class of objectives.

These glasses were generally known here at home as
'* duplex," or four system immersions, as distinguished
from the older form having a single front. Many of
these objectives, ranging in their claims as to balsam
angle from 82° to 100°, have passed through our hands,
and have been submitted to close and careful study ;
one object on our part being to determine, if possible,
whether a glass said to be of a lew balsam angle was
in any respect characteristically different from another
claiming a higher balsam angle, and in this way to
arrive at some determination as to the existence or val-
idity of the claims resting on the recognition of the
angle itself.

As a result obtained from close, tedious and pro-
tracted observations, dating from the present date back
to that of the first " duplex " made, we unhesitatingly
affirm that it is quite possible to distinguish the per-
formance of a duplex objective of 82° balsam angle,
from a similar glass of 100°, otherwise we would have
had no occasion to have introduced the subject at all.

Now, in the effect of balsam aperture, we recognize
in the high balsam angles precisely what has been at-
tributed to high air apertures, namely, a decrease of
working distance, as the balsam angle is increased, and

* Messrs. Tolles & Spencer are now (1880) making objectives of 120° balsam
aperture.

126 HOW TO SEE WITH THE MICROSCOPE.

a corresponding- increase of definition, when worked by
«xtrem<>ly oblique light over balsam mounts of " diffi-
cult tests." These characteristic differences in perform-
ance are so palpable, as to enable us to select in less
than fifteen minutes' use of two glasses over the Moller
probe plate, the higher-angled glass (balsam) from the
lower.

It has been claimed by some who have used the duplex
glasses, that the higher performance by central light is
obtained with those of tho smaller balsam angle. My
own experience does not authorize me to endorse these
conclusions. Certain it is, that when the higher angles
are used by central illumination, their immense power
of light will, if the matter receive not proper atten-
tion, defeat the glass, and again, even with oblique
illumination, the high-angled objectives require the
most careful attention and expert handling.

We are, therefore, prepared to endorse to some ex-
tent, referring to high balsam angles, the remarks which
have been quoted from " The Microscope and Its Reve-
lations."

FLATNESS OF FIELD.

It is, of course, desirable that an object known to be
flat should so appear when viewed under an objective.
The optician, however, has thus far found it impossible
to secure perfection in this respect, combined with the
highest aperture obtainable, and this might be urged as
an objection to the use of wide-angled objectives. The
slight err or shown by the glasses referred to, has much

FLATNESS OF FIELD. 127

rnore weight on paper than occurs actually in practice,
where the great increase in definition obtained causes
the slight deficiency in flatness of field to sink into
utter insignificance. Hence, in testing the qualities of
an object-glass, the flatness of its field would hardly be
called into requisition.

Nevertheless, flatness of field must have its due
weight, and the performance of a first-class objective
should not betray any serious error. It will be well,
then, when examining an objective, to look after the
quality referred to.

The careful testing of an object glass in this particu-
lar, is not such an easy and off-hand matter as might at
a glance be presumed; the manipulator may arrive at
incorrect results, and thus condemn a glass without
due cause therefor, and a word or two as to the proper
mode of conducting this test may not be amiss.

First, it is of the first importance that the object be
in itself flat when presented to the objective. Errors
may creep in — first, because the object is not in itself
flat, or, second, because it is mounted on an improper
slide, or on the cover thereof — very few slides are flat,
and covers are notoriously " in wind;" third, the stage
of the microscope may not be at right-angles to the
optical axis, and fourth, the eye-piece may not suit the
objective. To guard as far as possible against these
sources of error, proceed thus :

Select a fine ttage micrometer, having a band of lines
just about as close as the objective can well display
when viewed with nearly central light, and if you have

128 HOW TO SEE WITH THE MICROSCOPE.

no conveniences of your own, take this to the machin-
ist, or the watchmaker, either of whom will allow you
the use of a steel " straight edge," with which you will
be enabled to ascertain with tolerable exactness whether
one side of the micrometer is truly a plane. This done,
by the aid of a suitable "guage," you will also deter-
mine as to the other face. If, in a process of this kind
the micrometer betrays defects, it should be discarded
and another one chosen in its place. In our own prac-
tice we always use a Nobert test-plate, which has been
found to be very reliable.

To avoid the third source of error, view the lines,
selecting as close a band of lines as possible, and using,,
as before named, nearly central light, and the two-inch
eye-piece, with the micrometer placed horizontally and
vertically on the stage, examining the bands from end
to end as they appear in the field. Kepeat the experi-
ment, but reversing the micrometer in each position end
for end. Any error due to the pose of the stage is thus
made manifest.

Should you have reason to suspect trouble from the
eye-piece used, repeat the entire test on the stand of
some friend, always using the two-inch, or lowest eye-
piece. This ocular furnishing the more severe test.

Finally, let it be known that all the eminent makers,
both American and English, furnish glasses that are
not to be rejected for non-flatness of field. We would
rather trust to the reputation of these gentlemen, than
to the test conducted by the novice. A little practice
on the other hand on the part of the latter will not be
a waste of time.

MOUNTING OF OBJECTIVES. 129

MOUNTING OF OBJECTIVES.

Having glanced briefly at the optical portion, a few
words in reference to the mechanism of the instrument
may not be out of place.

Adjustable glasses are provided with movable or
stationary fronts, that is to say, in the process of re-
volving the correction collar the front lens also revolves,
or remains stationary, as the case may be. The station-
ary front being the most expensive mounting, it is gen-
erally adopted in first-class American or London glasses
of short focal distance.

In the use of objectives of tolerably long focal dis-
tance, the necessity for the stationary front is not so
apparent, and some first-class makers adopt either form
of mounting for such objectives. It behooves the buyer
to keep in mind this difference in the cost of the two
mountings, for of two glasses, both equal in optical
performance, the one adjusting with stationary front
ought to be the most costly.

Generally, the mechanism of the collar adjustment
should be first-class. There should be no "slip," "back-
lash," or " dead-point;" the collar should rotate with a
certain firmness of action, and yet run as "smooth as
oil ;" there should be no undue rubbing or grating, nor
"hitch or hindrance " of any kind. With a one-half
inch, or a four-tenths, a slight " slip" or " back-lash"
need not defeat an otherwise satisfactory objective;
but, on the other hand, nothing of this sort can be
allowed in the higher and first-class objectives. If the

9 Microscopy.

130 HOW TO SEE WITH THE MICROSCOPE.

collar be adjusted by the maker to rotate under high
pressure only, regard this with suspicion, and examine
for back-lash closely, or what is perhaps the better
^vay, get the opinion of a skillful mechanic.

The models of some of our American objectives are,
111 the opinion of the writer, far too large and clumsy,
.and the fronts too large and too flat. We decidedly
prefer the conical front — the more conical the better.
The new tenth of Mr. Herbert Spencer, which we have
before found occasion to mention, was, beyond all cavil,
the most beautifully mounted glass we had ever seen,
and in which the last-named objections were almost
wholly avoided.

NOMENCLATURE OF OBJECTIVES.

American and English microscopists usually class
their objectives on the basis of their focal length, it
being arbitrarily assumed that the inch s^lass worked
with ten-inch tube and with two-inch eye-piece, should
give an amplification of fifty diameters. Hence, the
half-inch glass would give one hundred diameters, the
one-fourth two hundred, the one-eighth four hundred,
the one-tenth five hundred, and so on. It very seldom
happens, however, that an object-glass will exactly re-
spond to the designation given it by the maker — some
opticians over, while others under-rate their instru-
ments ; and then again with an adjustable glass the power
will change in different positions of the adjusting collar,
the amplification being greater with the systems at
closed than when at " open-point." Even when due

NOMENCLATURE OF OBJECTIVES. 131

allowance has been made for this last condition, we
have seen English eighths having really higher power
than some American one-twelfths. Again, but a few
weeks since, we handled a foreign one-sixth which was
superior in amplification to a Spencer one-eighth. We,
here at home, have scolded a good deal at this state of
things, and at times have rated our English cousins for
thus underrating their objectives. It is quite unneces-
sary here to traverse the ground we have already dis-
cussed, to render it evident that as the objective ap-
proaches perfection, these nominal distinctions, based
on focal length, fail to have particular force. If, for
example, it were possible to produce a two-inch objec-
tive, which, under extremely high eye-piecing, would
more than do the work of our present tenths, then we
could afford to work pretty much with one objective,
and to the eye-piece look for the determination of the
power. Until, however, some such " possibility" shall
occur, our present nomenclature will be invested with
some force, no matter how variable this force may be.
It is, therefore, desirable sometimes to determine the
actual rating of an objective.

The method usually employed, is to place a stage
micrometer in position, using a ten-inch tube, and pro-
jecting the image by aid of the camera lucida on a screen
ten inches distant. Knowing, then, the actual value of
the divisions on the micrometer, we are enabled, by the
measure of the magnified image thereof, to determine
the amplification. This method is so well known and
so often practiced, we content ourselves with its gen-
eral mention.

132 HOW TO SEE WITH THE MICROSCOPE.

The method has its drawbacks. For instance, all
microscopes do not have tubes precisely ten inches in
length, especially when the objective is placed in posi-
tion; and then, again, if the problem be to determine
which of two lenses is the stronger, it may occur, and
pretty surely too, that one glass will have a shorter
setting i. e., "mount," than the other. There are ways
to dodge the difficulty, but the best method we have
seen of measuring objectives, where strict mathematical
accuracy is not a vital consideration, is by the use of a
formula, modified by Col. J. J. Woodward, and by him
given to the public through the columns of Silliman's-
Journal not long ago (Vol. III., June, 1872):

Formula :

v ML

* (M+l)'<
where F - - focal length, M — magnification without

-field-glass of eye-piece, and L — length between stage
micrometer, and micrometer in eye-piece.

If the UB" (one-inch ocular with its field-lens re-
moved, be selected, a micrometer ruled to one six-hun-
dredth of an inch will.be found to suit it very well.

It will be seen that the formula is extremely simple,
and quite within the comprehension of all; we, how-
ever, append an example or two, selecting cases which
have occurred in actual practice.

(1.) We lately had in hand a glass of Mr. Gundlach's,
made for a half-inch, and we desired to be assured as to
its true rating. Placing a suitable micrometer on the
stage, and selecting a one-inch ocular, with its field-
glass removed, but fitted with micrometer ruled to one

NOMENCLATURE OF OBJECTIVES 133

six-hundredths, and having brought the lines of the
stage micrometer in focus, we then measured the dis-
tance from micrometer to micrometer, finding the same
to be just ten inches, and on comparing the divisions of
the stage micrometer with those of the eye -piece, we
found those of the stage micrometer to be amplified
eighteen linear. Now, working out the formula, and
substituting for the symbols their proper values, we
have

Focal length= !?±12 = 1§? =-5 in. or i inch.

Hence, we find the glass exactly to the rate given it by
its maker.

(2.) In a similar manner it was desirable to test a
(so-called) one-fifth objective. Proceeding just as be-
fore, simply changing objectives, we measured again the
distance from micrometer to micrometer, getting again
just ten inches — a matter of chance, however, and one
not likely often to occur. Comparing the two microm-
eters again, we get an amplification of the stage lines
of thirty-eight linear. Substituting values as before
we now have

Focal length = -3-8±I5 = -M. = .25 in. or i inch.

oo^ lo^il

For the purpose of developing the capacity and value
of the formula, we will now repeat this example, but
in place of using a distance of ten inches, we will
arrange to secure in lieu thereof a distance of twelve
and one-half inches. We now find the amplification, as
shown by the two micrometers at this greater distance,

134

HOW TO SEE WITH THE MICROSCOPE.

to be forty-eight linear, and substituting this value, we
have

Focal length =

«<>

* in. again.

Either computation gives the same results (rejecting
fractions too small to affect things sensibly), and we
see, too, that the glass sold for the one-fifth is really
but a true fourth; and, furthermore, it is evident that
a change in the distance of the two micrometers — in
other words, working with different lengths of tubes —
does not practically affect the results.

TABLE OF THE MAGNIFYING POWERS OF SINGLE CONV6X

LENSES.

The first column gives the focal length for parallel
rays; the second, third, fourth and fifth, give the mag-
nifying powers at ten, twelve and a half, twenty-five,
and fifty inches respectively, the last three being from
the American Journal of Science and Arts, as before
mentioned, while the second was computed by the Hon.
J. D. Cox, of Ohio, and by him presented to the
author.

Kocal Length

Magnifying

Magnifying

Magnifying

Magnifying

for

Powers

Powers

Powers

Powers

Parallel Rays.

at 10 inches.

at 10!4 inches.

at 25 inches.

at 50 inches.

1

2

3

4

5

3 inches.

1-331

1-50

6-17

14-59

2

3'00

4-00

10'40

22-95

MAGNIFYING POWERS.

135

1 1-2 "

4-67

617

14-59

31-30

1

8-00

10-40

22-95

47-99

2-3 "

13-00

16-69

35-47

72-98

1-2 "

18-00

....

....

• ...

4-10 "

23-00

29-21

60-48

122-99

1-4 "

38'00

47-99

97-98

197-99

1-5 "

48-00

60-48

122-99

247-99

1-6 "

58-00

72-98

147-99

297-99

1-8 "

78-00

97-98

197-99

397.99

1-10 "

98-00 -

122.99

247-99

497.99

1-12 "

118.00

147-99

297.99

597.99

1-15 "

148-00

185.49

372-99

741-99

1-16 "

158-00

197.99

397-99

797.99

1-18 "

178-00

222-99

447-99

897-99

1-20 "

198-00

247-99

497-99

997-99

1-25 "

248-00

310.49

622-99

1247-99

1-50 "

498-00

622-99

1247-99

2497-99

By the use of the preceding table one is able to meas-
ure the focal length of any objective, and without in-
volving the trouble of computations. In ordinary cases
it will be only necessary to see that the two microme-
ters shall be exactly ten or twelve and one-half inches
apart. The amplification in either case being noted, we
enter the table under the proper head, and correspond-
ing to the amplification will be found the focal distance.
For instance, taking the first case we have presented,

136 HOW TO SEE WITH THE MICROSCOPE.

that of Mr. Gundlach's objective, we worked it a dis-
tance of ten inches, and observed an amplification of
eighteen linear. Entering column two of the table, we
find at a glance eighteen to be opposite to focal length
of one-half inches.

In the case of the so-called fifth, with the two micro-
meters at ten inches distance, we observed a magnifica-
tion of thirty-eight linear ;' entering the second column
of the table again, opposite thirty-eight, we have the
focal length, equal one-fourth inch. To the last com-
putation we worked the same case, but with the micro-
meters twelve and one-half inches distant; in this case
observing a magnification of 48. Entering the table
in column third, opposite to 47.99, we have the same
focal length as before, viz., one-fourth inch.

It often occurs that many first-class stands cannot be
worked at a distance of ten inches with objectives of
ordinary lengths. In this case use the twelve and one-
half inch distance, which can always be obtained by
using the draw tube.

CHAPTER III.

OBJECTIVES CONTINUED.

What constitutes a really superlative wide-angled
objective? It has been our fortune to reply to this
question upwards of ten thousand times, and it may be
true that no two of these responses have been exactly
alike. In the present essay let us tret close to the reader,
introducing a little gossip, and, at the same time, seek-
ing a little relief by avoiding expressions which are
getting to be stereotyped, such as the " writer,"
" this," " the author," "that," etc., helping ourselves
freely to the first person singular, about as one would
when writing to a friend.

It has been already shown that there are two classes
of high-angled glasses — namely, those having balsam
apertures, say up to 100°, the other class responding to
air angles, up, say, to the "impossible," 180°. And,
first, let us consider the objective ot high balsam angle.

I have, in advance, stated that these glasses necessa-
rily have a very short working distance. But this re-
mark must not be swallowed whole; let it be taken
rather with a "pinch of salt," keeping this little fact
well in hand, that there are wide-angled balsam aper-
tures, having greater working distance than will be
found present in other objectives of the same nominal
focal length, and having, too, no really wide air angles.

137

138 HOW TO SEE WITH THE MICROSCOPE.

Iii comparison with such as these, the high balsam
apertures have nothing to fear. As to working dis-
tance, a vast amount of misguided effort has been ex-
pended in the vain attempt of trying to compare one
kind of an objective with another; for instance, a wide-
angled air aperture with objectives of narrow air
angles. Hence, we have had nothing but muddle and
confusion. I repeat what I have before printed, that
any attempt of the kind is as futile in its very nature
as it would be to compare a " turnip with an orange. "
It has, therefore, been my aim, however imperfectly I
may have succeeded, to lead my readers along one road
at a time, and this " objective" point has been steadily
held in view while writing this little book, and up to
the present writing, whether success has attended the
effort or not, I claim some credit for having essayed in
this direction.

" He venous a nos moutons." — I repeat, then, that of
two superlative objectives having balsam angles ranging
from 82° to 100°, the rule presented holds good, i. e.9
that the higher aperture will have the shorter working
distance, or, in other parlance, the gain in aperture will
be accompanied by a sacrifice of working- distance.

Now, we all know what is lost with the decrease of
working distance. Let us, therefore, seek as to what is
gained by the increase of aperture. First, we gain a
wonderful increase in intensity of definition; an increase
in definition too, entirely unapproachable from any
other direction. In this particular these glasses stand
alone and defiant. Secondly, their immense power of

OBJECTIVES CONTINUED.

light, superlatively corrected as they are, enable them
to be used under wonderfully high eye-piecing, and
with comparatively slight loss of either light or defini-
tion, while by the aid of these high oculars, the greatest
magnifications are obtainable, and in these particulars
also, do these objectives again stand alone and defiant.
' Somehow, among the few who have paid attention to
the claims of the balsam apertures, it has got to be the
popular impression that it is the particular province of
these objectives to bear high oculars, the impression
having force in a restricted, or limited sense — to wit,
that there is nothing gained really by the use of high
balsam angles under low or medium oculars.

Any idea of this sort is totally in error, for even
under a low or medium eye-piece, the higher balsam
angle will demonstrate its presence by an increase in the
intensity of definition, while its greater power of light
is in itself 'a power capable of being turned to certain
necessary and useful purposes. I have already stated
that it is quite possible to distinguish the one glass
from the other, and, I might have added, " under low
or medium oculars."

But, as I have said, with all this gain, there is an ac-
companying loss of working distance. But this is not
all ; those who have been accustomed to work all their
lives with objectives of low or medium apertures, might
with good reason, claim that the high balsam angles
are "exceedingly inconvenient to use." Palpable is
the fact, that the slightest error in the collar adjust-
ment, or in the management of the illumination, will

140 HOW TO SEE WITH THE MICROSCOPE.

suffice to defeat the maximum performance of the bal-
sam apertures, and the higher the balsam angle, the
greater the " bother " attending their use.

Nor is there anything so exceptional in all this. In
any instrument of precision, when, by successive im-
provements, we gain width of effective range, and,
simultaneously, a nearer approach to accuracy of deter-
mination, then, in ninety-five cases out of the hundred,
do we, in like manner, increase the complications of
the instrument; thus introducing " inconvenience " and
" bother," and, be it known, an accompanying call for
skilled manipulators.

We often hear another remark — to wit, that those
•owning and using the class of objectives we are now
considering, do nothing else than " fight them." Before
attaching any definite force to this remark, it will be
well to inquire, " for what purpose is \he battle!" Is
it to determine which of two objectives, differing in
construction, but supposed to be nearly alike in per-
formance, is the better one, and with the purpose
(avowed or otherwise) of rendering some contribution
to a scientific end; or is it that "A" battles " B," the
object being on the part of " A" to assure himself that
his glasses are not behind the age in quality of per-
formance; or, again, may it be that " C," being re-
quested by his inexperienced friend "D" to select for
him an objective in every respect fully up to the times?
Or, to mention a very possible case, does "E,"who,
having a few hours of daily leisure, desires to appro-
priate the same to the study of object-glasses, with the

SUPERLATIVE WIDE-ANGLED OBJECTIVE.

view of perfecting himself in the manipulations of the
same, that he may in turn render his observations and
experience of value to those who devote, their spare
time to investigations with the instrument? If these
are the ends in view to be accomplished, then I say,
" fight objectives," and furthermore that " E" need not
be ashamed of his occupation. On the other hand, if
objectives are fought for other and baser purposes, that
is no aflair of mine. I cannot help it, and the objective
is not to blame.

I claim, then, that the high balsam angles are indis-
pensable in the studies of the advanced investigator ;
they alone, " bother or no bother," are the ones for the
work. Let the reader keep constantly in mind that, in
the study of difficult and delicate structures, the slight-
est superiority of definition is of vital importance. A
first-class objective of high balsam angle will show,
clearlv and accurately, details in an object, which, from
their extreme tenuity or transparency, would be totalty
invisible when viewed under an objective having but air
angle.

To sum up: We thus arrive at the conclusion that
objectives of high balsam angles, have, as compared
with others of less balsam angle, a shorter working dis-
tance, and in general are " inconvenient and bother-
some to use; nevertheless, that their use cannot be dis-
pensed with in the study of delicate and difficult struc-
tures, and it may be further stated that these are the
glasses suitable for the study of difficult diatoms, the
display of the Nobert nineteenth band, and the like.

142 HOW TO SEE WITH THE MICROSCOPE.

Thus far, whatever force may attach to the elements of
* ' inconvenience " and "bother," of which we have
heard so much, I have allowed full play and weight ;
but let the reader not lose sight of the fact that those
accustomed to the use of adjusting glasses never aban-
don them to return to their first love, nor do they re-
gard the process of adjusting a superior objective as
being in any way or shape a " bother" or " inconven-
ience." It may be well, right here, to state a bit of
personal experience. I am in the habit of putting ad-
justing glasses in the hands of my pupils at the earliest
possible moment ; not that they will accomplish more
with them for a time than would be the case with those
non-adjustable, but in order that the pupil be early
brought in contact with them, and thus, by degrees,
get accustomed to their use. By adopting this course,
the tyro learns, in clue and proper season, an important
lesson, to wit, that there are some things to be done
besides putting an object at one end of the tube and
the eye to the other in order to see what's what. Now,
it often happens that there may be more pupils in the
laboratory than adjustable objectives, and thus, per-
force, a student or two will have to fall back on the
non-adjustable. When this state of things occur there
is inevitably indications of discontent, and it is never
on the part of those pupils occupied with the adjustable
objectives.

So much for the " inconvenience" and " bother."
Now, let us get after that other elephant — working
distance. I have granted that wTith the higher balsam

SUPERLATIVE WIDE-ANGLED OBJECTIVE. 143

apertures there is a loss of distance. Now I propose
to discuss this " loss " from a practical point, and in so
doing shall state facts, including names and dates.

On the 22d of March, 1878, I received from Messrs.
C. A. Spencer & Sons, a one-tenth objective of high
balsam angle. This glass was made to my order, and
for the Hon. J. D. Cox, of Ohio. Before sending it to
its destination I " fought it." Its performance was as
follows: Worked over the balsamed Moller probe
plate, on the Zentmayer histological stand, with the
mirror-bar swung to 31° from axis, I saw distinctly the
striae of Nos. 18 and 19 of said plate, nor had I any
doubt as to thus seeing the No. 20, the illumination
being a common small coal-oil lamp. The light was
taken direct from the mirror.

Worked over the same Moller plate, but with the
Wenham reflex illuminator (an instrument devised for
shutting out all pencils having air transmission), I
saw the transverse striae of the No. 20 of said plate
handsomely using powers from 1,000 to 4,000 diam-
eters.

Tested over a fine slide of English podura, using
ordinary illumination, and nearly central, I had the
finest display I had ever witnessed.

Worked over navicula angulata, with "dead central "
illumination,, it gave me instantly the markings very
handsomely.

Worked over a dry mount of amphipleura pelliicida.
These shells surrendered at discretion ; ordinary oblique
illumination. Substituting a balsam slide of this

144 HOW TO SEE WITH THE MICKOSCOPE.

diatom, placing the same in position under the stage
of the bistological, I got handsome resolutions with
the mirror, at say 80° from axis, and also when the
swinging-bar was posed so that more than half the
mirror was above the stage.

Tested for working distance. I found the same to bo
.015, equal, say, to one-sixtieth of an inch.

There were very many other " rounds" to this fight,
which are purposely omitted as having no bearing on
the subject in hand. The reader has before him the
work of the objective by central, centrally disposed,
tolerably oblique and decidedly oblique illumination.

Now, thus having the work of the objective before
us, it is palpably evident that it has all desirable work-
ing distance. Surely no one but a bungler would at-
tempt to cover a nice mount with glass over one one-
hundredth of an inch in thickness, while, with such a
cover, the one-tenth will have plenty of room and to
spare; and if we compare the glass named with the
usual run of immersion tenths, it will be obvious that
there is no loss of wrorking distance nor any sacrifice
thereof in any way, shape, or manner.

OBJECTIVES OF LOWER BALSAM ANGLE.

These, when compared with the glasses we have just
had under consideration, will be found to have greater
working distance, as has been before stated; and with
this increase of distance there will be greater focal
depth — the so-called ll penetration " of the books.
Now, in the preliminary investigation of many objects,

OBJECTIVES OF LOUEil BALSAM ASGLE. 145

this is a, desirable quality in a glass. It enables us to
search through an extemporized mount in the least pos-
sible time. And then, again, we are less liable to allow
important details of structure to escape our attention.
These are advantages, and must be recognized as such;
but, per contra, let it be remembered that in subse-
quent examinations it often becomes quite as important
that this quality of penetration should be absent. For
instance, when it is desired to study structures situated
in one plane, and one plane only, the less of penetra-
tion the better. I have not space to enlarge on this,
but let the reader not forget the fact. The glasses of
the lower balsam apertures are really the easiest to
manage, and yet are effective and adequate for a large
class of work. They have less power of light, and
hence do not " stand up" so well under high eye-
piecing, nor have they the same exquisite intensity of
definition. In a certain sense, the diminution of defini-
tion is very slight, indeed scarcely to be noticed (if at
all) when examining tolerably vigorous tests. Hence,
they are quite adequate for the resolution of nearly all
the recognized test objects when mounted dry. It is,
then, over exceedingly thin, faint, delicate, and trans-
parent tests that the higher angles assert their suprem-
acy.

If the general definition as to what constitutes a
high-angled objective, given on a preceding page, be
accepted, then there remains room to discuss a class of
objectives of such focal lengths, nominally, as defy any
expert effort on the part of the optician to extend

10 Microscopy.

146 HOW TO SEE WITH THE MICROSCOPE.

their aperture to any thing like an approach to 180°.
Among such may be included the two inch of 25°, the
one and one-half inch of 37°, the one inch of 40°, the
two-thirds of 45°, the one-half inch of 100°, the four-
tenths of 150°, and so on. All the glasses above
named may be considered as high-angled objectives.
They should be nicely corrected, fully up to the limits
of the aperture claimed for them, and, as compared
with similar lenses of narrow apertures, they should
possess a much greater power of light, and bear higher
eye-piecing; and, let it be borne in mind, that of the
above-named objectives, the one having the greater dis-
tance will be "endowed" with the greater "penetra-
tion."

And right at this place let us see what the " power
to bear high eye-piecing" means. To illustrate this,
we will take a case such as might happen in practice.
For example, I desire to see the transverse lines of
pleurosigma ~balticum, and, as mounted on the Moller
balsam test plate, their striations being from 31 to 34,
in .001 Eng. inch. ]STow, I attack this with, say, a
real good low-angled one-half inch, and find that I can
just get a glimpse of the lines with the one-half inch
eye-piece. I then apply the one-quarter inch eye-piece,
and find that the view is not nearly as satisfactory as it
was with the lower ocular; hence I conclude that the
one-half inch eye-piece is as high as the objective will
bear. Now, removing the one-half inch objective, we
will substitute a two-thirds, but of higher aperture.
With the latter glass, using the one-half inch ocular, I

OBJECTIVES OF LOWER BALSAM ANGLE. 147

get better shows than was the case with the former ob-
jective, and on applying the one-quarter eye-piece I
have better definition yet. There is some loss of light,
to be sure, but there is enough left to do the work, and
in a more satisfactory manner than occurred when the
lower eye-piece was in position. I take this case as an
illustrative one, because I have used it repeatedly with
my visitors, and the demonstration has, 1 believe,
always been accepted as satisfactory. It will be noticed
that thus using the two- thirds, the power applied at
the eye-piece was greater than the rating of the objec-
tive employed, and a tolerable test for an object-glass of
such low nominal power. We have here, then, in the
experiment cited, an illustration of what may be said
to be k< power to bear high eye-piecing."

There is a general and indefinite idea afloat, that
there is something about high eye-piecing which ought
to be condemned. Without making any special attack,
it ir ay be admitted that observers "came honestly by
it." The facts warrant this much: powder — z. e., ampli-
fication or magnification — when not wanted, is to be
condemned, and it matters not how obtained, whether
at one end of the tube or the other. On the contrary,
if any thing valuable is to be obtained by amplification,
then we are auth orized to use it, and to the best advan-
tage apply it at either end of the tube, as the case may
warrant. There seems no more propriety in the con-
demnation of high eye-piecing per se than ought to ob-
tain in the use of objectives of short focal length.

148 HOW TO SEE WITH THE MICROSCOPE.

ADJUSTABLE OBJECTIVES.

The generally received notion in regard to these
glasses is, that they are provided with an adjusting
collar, so that they may be " corrected for aberrations,"
due to the thickness of cover employed on the mount
under observation. This is all true in a certain sense,
and to a certain extent only. If we examine the same
object under the same objective (a first-class glass of
high aperture), but through covers of varying thickness,
we will find that the very best performance of the glass
wilL be obtained when worked over a particular thick-
ness of cover, and that any change from this particular
thickness will interfere with the performance of the
lens, no matter how perfect the corrections in each case
may be made. My own experience teaches me that the
maximum definition is only obtained when the objec-
tive adjusts at or near that point in the collar adjust-
ment which corresponds to the maximum aperture of
the objective. Now, in most glasses of high angles the
maximum angle will be found at only one position of
the collar. I say " most objectives," for we have a
one-tenth made by Mr. Tolles, that has maximum angle
nearly at any point within the range of its collar ad-
justment. We have also a one-sixth by the same
maker, which has maximum angle only at the " closed
point," the aperture decreasing rapidly as the collar
approaches " open," and with the decrease of angle there
is an accompanying decrease of definition and effective
force of the objective.

ADJUSTABLE OBJECTIVES. 149

Here we have an argument in favor of wide angles
which has been in the past quite lost sight of, and was
for the first time presented to the public by the writer
in one of his monthly contributions years ago ; but all
this is foreign to our present purpose.

Now, in the case of the one-sixth of Mr. Tolles,
should it be attempted to use this glass over the thin
cover of the Moller probbe plate, the result would only
be to defeat the performance, for the glass would "cor-
rect" within three divisions of "open-point." But,
per contrary, if we desire to secure the best definition
of the said objective, and over the said plate, it becomes
necessary to supplement by thicker cover (making sure
of optical contact by the use of water or glycerine),
until the glass shall " correct" at or near " closed."

Hence, it occurs that it is essential that the observer
who proposes to employ objectives of wide apertures
should pay some attention to the condition of things ;
that he should know precisely over what covers he will
be enabled to get the maximum performance. In
short, to ascertain where he may find the maximum
aperture of his objective.

And to this end, we propose to aid and assist, as far
as possible, in some future remarks we shall have occa-
sion to make regarding the manipulations of the objec-
tive. During the past twelve years the author has
received hundreds of letters from as many individuals
commencing the study of the microscope, desiring such
information as to the best way of making an invest-
ment as may pertain to the selection of stand, objec-

150 HOW TO SEE WITH THE MICROSCOPE.

tives, etc. The said letters have met with a prompt
response, and, as has before been stated, perhaps no
two of these have been alike. In each and every case
there has been some dissimilarity of circumstance, or,
on the other hand, we have suffered some change in our
own views. Be all this as it may, the experience of the
last two years enables us to speak more precisely to
the point than before, and we now endeavor to respond
to the interrogatory — *' What shall I procure for an
outfit?"

' There can be no general rule that will apply to all.
Let us take the following as a typical letter for con-
sideration :

"DEAR SIR: I have read some of your contribu-
tions to the American Journal of Microscopy. . . .
I am a physician of ten years' practice ; am located in
a town of some ten thousand inhabitants. I am satis-
fied that I ought to know enough about microscopy to
enable me to examine intelligently urinary deposits,
cancerous growths, etc., and to this end do I propose
to purchase the necessary equipment. Any informa-
tion that you may be pleased to give me, will be with
pleasure received," etc.

Now, I would answer this letter, and did answer it,
thus : When you buy a stand get one that you will
have no occasion to sell at a ruinous sacrifice. I rec-
ommend that you purchase one of the cheap and mod-
erate-priced instruments, and, at the same time, one
that will do any and all work. Such a stand ought not
to cost, with one eye-piece, more than forty-five dollars

ADJUSTABLE OBJECTIVES. 151

(and such are described in this little book). Now, as
to objectives. You can do all the work named with a
one-inch of tolerably low angle, costing you, say, some
$7.00; and a real good three-tenths of 70° aperture,
which will cost you, say, $11.00. The chances are,
however, that as you become familiar with the use of
the instrument, thereby learning its value to you in
your daily professional practice, you will feel an inclin-
ation to dip somewhat deeper into the problems which
will most assuredly surround you. In your examina-
tions of urines, you will get glimpses of bacteria ; you
may meet with structures which you are almost assured
are " pale hyaline " tube casts ; and you naturally desire
a little more amplification and definition thereon to
enable you to pronounce with certainty. In fact, you
now want such a glass as a dry one- fourth of 110° or
120°, and adjustable. Now, to use this glass to advan-
tage, you have first to become familiar with its manipu-
lations. It will be requisite that you arrive at some
knowledge of this before such an objective can be of
much avail to you. Now, if you purchase the one-
fourth recommended, you will still have room for the
employment of the three-tenths, but you will have to
study the use of the one-fourth just the same as if you
had never seen an object-glass. Hence, I had rather
recommend that you purchase the one-fourth at the
start, and thus get early accustomed to the use of ad-
justable glasses; and in this latter case it will almost
assuredly occur that you will eventually desire to
employ glasses of the widest apertures, and the expe-

152 HOW TO SEE WITH THE MICROSCOPE.

rience you have gained with the use of the one-fourth
will be of the utmost value to you. Moreover, the
one-fourth, too, will continue to be a useful interme-
diate glass.

And thus in replying to all my correspondents, I
recognize the importance that one and all shall early
become acquainted with the manipulations of adjusting
glasses. To accomplish this they must use objectives
of a reliable class, i. e., such as will respond promptly
to change of collar-adjustment, keeping well in mind
the importance of buying nothing to be discarded or
thrown out of use in the future. In the case under
consideration, it will happen, in nine cases out of ten,
that in less than two years the buyer will feel that he
needs a first-class inch, or perhaps a two-thirds, in
which event the old inch will be of great service as a
sub-stage condenser, providing that the stand has been
selected with this end in view.

It may further happen, in truth it will be likely to
happen, that in the course of one or two years, my
correspondent will either push his own observations or
desire to keep pace with those of others, and over
structures of the most delicate and " difficult" charac-
ter, and now he will need a one-sixth or a one-tenth of
the widest possible aperture. Allowing this to occur
he will have expended but $110, which is less than the
usual cost of a nominally first-class one-sixteenth, and
all the glasses on hand will still be of service. Besides
all this, he is well armed and equipped for any work
requiring powers from 50 to 5,000 diameters, and there

ADJUSTABLE OBJECTIVES. 153

will be no objectives on hand that will not be worth
their cost.

The above programme seems to me to fill the bill
as well as any other that could be named, and is prac-
tically the same as that followed in my own practice,
having daily a large amount of work over urinary de-
posits, a considerable portion of which does not require
-excessively fine definition, and time being very much of
an object, I employ, in addition to the glasses named, a
cheap, but good and reliable half-inch, say of 35° or 40°.
With this glass I am enabled to perform much prelimi-
nary work over liquids, and am able to dispense with
•covers, and the objective, from its long working dis-
tance, is out of the fumes of the re-agents constantly
in use. The half-inch is thus of great service, as a
time-saver — in short, as a convenience.

Finally, let it be understood that I have no war to
make on objectives of medium apertures. We have
stated our experience, and it must pass for what it is
worth. The principal point which I desire to impress
on the mind of the reader, is that, for the higher class
of investigations, the objectives of wide apertures stand
alone, unapproachable and unexcelled; that they alone
are the instruments for such work, and this, too, regard-
less of the character of the illumination employed, be
it central or oblique. Another point is that the use
of the high angle enables the observer to cut down the
numerical force of the glasses employed, thus saving
unnecessary expense. We wish also to render the fact
obvious, that a wide angle glass requires time, study,

154 HOW TO SEE WITH THE MICROSCOPE.

and attention, and that the manipulations of the same
are not acquired in a day.

In niy intercourse with microscopists, I have nearly
always found one idea salient. The general question
has been and now is, «* How shall we contrive to save
expense ; where can we buy the cheapest? "

It seems to me that these considerations must eventu-
ally force the wide apertures into use. I was about to-
gay, " There's millions in it." For example, we know
of a microscopist who has, by purchase, from time to-
time, acquired a battery of some 35 or 40 objectives.
Now, allowing the cost of these to average $10 each —
not a high estimate — the owner has thus paid out some
$350 or $400 for objectives alone ! While one-half that
money, expended in glasses of the highest apertures r
would have enabled our friend to have accomplished
any and all work that can be effected with his entire
battery. And unless I am greatly mistaken, the wide
apertures would carry the day, and with flying colors.

This is no solitary case. We have in very many in-
stances been called on to select wide-angled objectives
for our friends and correspondents, and in each and every
case — there have been no exceptions — we have received
assurances from the parties interested, that there would
have been money saved had the facts been known in
time. Says one: " My one-fifteenth that I bought two
years ago is a dead letter; what shall I do with it? I
can't sell it for anything like what it cost, it would be
perpetrating a swindle !" Says another : " If I had met
you thirty days ago I would be a hundred dollars better

ADJUSTABLE OBJECTIVES. 155-

off than I am to-day; you have made me sick of my ob-
jectives." I say, therefore, that it seems to me that this
string must pull, to the end that the microscopist, who
desires to invest his money to the best advantage, will
be driven to the use of the wide apertures, no matter
how strongly he may have "become prejudiced in another
direction. We believe and earnestly hope, that in pre-
senting the subject to the readers of this little work, we
have done them a good honest turn, and one that will
be appreciated.

Before entering on another part of the subject of this-
book, we desire to add that the views thus set forth are
the result of practical expeiience. Here is no specula-
tion; but, on the other hand, the reader has before him
the fruit of protracted and close study. The time was
when we were almost alone in our opinions, but that
date is numbered with the past. Among those who-
had read his printed articles in their various periodical
forms, and have subsequently visited him, ;< to see for
themselves," he can name many of his dearest friends,,
all of whom have, in turn, placed the writer under
countless obligations. And, right here, by the way,
let me say, that, as an interesting and enjoyable pastimer
that of " fighting objectives " is, when occasionally in-
dulged in, second to no " 2.25 " race on record! But
of any of the good things of this world — " enough is a
feast."

156 HOW TO SEE WITH THE MICROSCOPE.

EYE-PIECES.

It would be a real improvement to assign to individual
*eye-pieces their actual power expressed in inches, and to
dispense with the arbitrary and indefinite nomenclature
formerly, and, to a great extent, at present in vogue.
Thus, let the two-inch have the same magnifying power
.as a simple lens of two inches focus, and similarly as to
the other oculars used. Messrs. Spencer, Tolles, Sidle,
.and we believe Zentmayer, adhere strictly to this plan.

We use principally the inch, half inch, and one-fourth
inch. For those oculars above the inch in power, we
greatly prefer the solid eye-pieces. We have also the
two-inch and the solid one-eighth inch. The former is
however, but very seldom used ; in fact, in our own
practice, it is seldom wanted or even thought of. The
solid one-eighth, although not in general use, cannot be
dispensed with when working with sunlight illumina-
tion in conjunction with objectives of high balsam angles.
We cannot too strongly recommend that every attention
be bestowed as to the quality of the solid oculars, and,
.as a rule, that they be made expressly to order.

It occasionally happens that stands fitted with poor
objectives are placed in the market for sale, while to
accommodate the quality of the objectives the powers
of the oculars are let down considerably — thus illus-
trating the truth of the well-known proverb, c'est le
premier pas qui coute.

Let the purchaser look well to these points before
•consummating an investment.

CHAPTER IV.

MANIPULATIONS — WENHAM's REFLEX ILLUMINATOR.

This instrument, and its various modifications, having*
come into very general use in this country, we give the
following cut and description, taken from Dr. Carpen-
ter's work on " The Microscope and Its Revelations:"

"A very ingenious and valuable illuminator for high
powers has been recently devised by Mr. Wenham, and
constructed by Messrs. Ross. It is composed of a glass
cylinder, half an inch long and four-tenths in diameter,
the lower convex surface of which is polished to a radius
of four-tenths. The top is flat and polished. Starting
from the bottom edge, the cylinder is worked oif to a
polished face at an angle of 64° ; close beneath the cylin-
der is set a plano-convex lens of IJ-inch focus. When
parallel rays are thrown up through this apparatus from
the mirror, they impinge on the upper surface of a glass
slide at an angle of total reflection ; but if a suitable
object adhere to that surface, the light reaches it on an
angle that admits its passage. The object is then seen
brilliantly lit up upon a dark ground, and many fine
markings, that escape notice with other methods, become
very distinct. It is advisable to rotate the apparatus
until the best position is obtained. Some skill and
practice are required to use this apparatus to advantage,
but it will amply repay the trouble of mastering its

158 HOW TO SEE WITH THE MICROSCOPE.

difficulties. It is best suited to thin and flat objects ;
with those that are thick and irregular, distortion is
unavoidable. Although specially designed as a dark

ground illuminator, good effects can with care [and by
the use of suitable objectives], be obtained lor such ob-
jects as difficult diatoms, in balsam or dammar. But
the effect is that of very oblique transparent illumination"
We have preferred to give the above description from

WENHAM'S REFLEX ILLUMINATOR. 159

Dr. Carpenter. The interpolation within the brackets,
and the italics are our own.

As is above set forth, this instrument was designed
by its maker for a dark ground illuminator, and for use
with high powers; was made and sold for this purpose,
and was generally so used. Shortly after their intro-
duction into this country, Mr. Samuel Wells, of Boston,
Mass., made the discovery that the " reflex" when
worked with certain very high-angled objectives, could
be made to give a brilliantly-lighted field, accompanied
with beautiful resolutions of the severest tests, when the
latter were mounted in balsam, the effect being, as Dr.
Carpenter most justly observes, " that of very oblique
illumination."

As is evident from an inspection of the cut, the instru-
ment can be variously modified in its working, simply
by changing the angle of the facet. The fact, too, ap-
pealed almost simultaneously to all, that a serious objec-
tion to the instrument was that it could be only used
over balsam mounts, and of course with objectives of
the highest angles. The " reflex *' was therefore modi-
fied by the London opticians to suit the angles of their
leading objectives, and, at the same time, or at least
shortly after, similar modifications of the instrument
were made here. There has been an effort here at home
to claim, on the part of our opticians, some originality
of design in the construction of these various modifica-
tions. The entire plan, however, belongs to Mr. Wen-
ham, and the simple changing of the angle of the facet
does not authorize any claim of invention The author

160 HOW TO SEE WITH THE MICROSCOPE.

has used several of these instruments ; the first one wa?
made by Mr. Tolles, the angle of facet being 26° An-
other one made some little time afterwards had facet of
18°. Subsequently Messrs. Spencer have made him sev-
eral having angle of 15°. The genuine instrument, as
made by Mr. Wenham, is only suitable for use with
objectives of high balsam angle, while those of the
modern form can be employed with more or less suc-
cess in conjunction with glasses possessed of tolerably
wide air apertures. We have spent a great deal of time
in the study of this instrument, including the several
patterns named, and we find that when used with glasses
of the highest balsam apertures, such as are made by
Messrs. Spencer or Mr. Tolles, and over the severest
tests, such as amphipleura pellucida, the resolutions are
quite as strong and satisfactory when the illumination is-
obtained from the modified " reflex" as when the instru-
ment described by Dr. Carpenter is selected, while the
latter has the serious disadvantage of being adapted for
use over balsam mounts only.

The instrument can be adapted to almost any good
and reliable stand, even should the latter not be pro-
vided with centring apparatus; yet if the sub-sta^e
collar be itself well centered, a little ingenuity on the
part of the observer will secure good results. It is,
however, a great convenience, when using the " reflex,"
to employ a stand allowing the sub-stage to approach
the slide or to be drawn away therefrom.

To use the " reflex," place it in the sub-stage fitting,
select a low power, say a half-inch or a two-thirds, and

WENHAM'S REFLEX ILLUMINATOR. 161

one that you know centres well with the objective to be
employed. With such a glass see if the central mark
placed on the instrument by its maker occupies the
•centre of the field. If but slightly out of centre, a very
slight tipping of the instrument in its sub-stage fitting
will often be all that is necessary. If the stand has
centring screws these will come well into play. .We
have found it desirable to secure perfect centring, and
at the same time make sure that the plane face of the
facet is parallel to the right-hand edge of the stage, and
adjacent thereto. Having placed a small drop of gly-
cerine (which is preferable to water, as it does not dry)
on the top of the facet, and having placed the object
and slide in position, the " reflex " is made to approach
and the glycerine to contact the slide. It is better not
to allow the top face of the instrument to actually touch
the under surface of the slide, still keeping it, however,
so close thereto that the drop of glycerine shall be
considerably flattened.

We are now ready to screw on the object-glass, and to
make immersion contact with the cover. For illumina-
tion we need one of the lowest and smallest kerosene
hand-lamps that can be found. If the stand is small
and low, it will become necessary to place it on a suit-
able box, the tube inclined to a convenient angle. Re-
moving the mirror, use the light direct from the lamp
keeping the latter for the present in nearly or quite a
central position. If, on looking through the eye-piece,
there be found a lack ot illumination, the trouble can
be rectified by moving the lamp slightly. Having

11 Microscopy.

162 HOW TO SEE WITH THE MICROSCOPE.

thus got light enough, next proceed to find your object
and to focus the same, and if the approximate correc-
tion for the objective is known it will be well now to
apply it.

Next, we proceed to attempt the proper display of
the object, Seize the lamp with the right hand, turn
the edge of the flame edgewise to the illuminator, and
move the lamp bodily, sliding it on the table in all
directions, to the right, to the left, towards the stand
away from it. If, while thus manipulating the lamp,
the field should be lighted with a succession of colors,
blue, red, green, etc., you may be pretty sure that things
are working well. Making sure, now, that the edge of
the lamp flame is turned to the " reflex," and still grasp-
ing the lamp with the right hand, and the fine adjust-
ment with the left, try the effect of very small move-
ments of the lamp ; these will be followed with a change
of color in the field. Supposing, now, that the distance
of the lamp from the stand is just right. We will find
that by pushing it horizontally and parallel to the front
edge of the stage, towards the left, we shall shortly have
a blue field, while with a little further shove in the
same direction we lose our illumination. Now it is in
such positions, and just at the point where the illumina-
tion begins to decrease, that I get the strongest resolu-
tions of severe tests. If we now retrace the path of the
lamp, carrying the same towards the right, the field will
become tinged with red, and by pushing the lamp still
farther thereto this will deepen, while another move-
ment of the lamp in the same direction will cause the

THE WOODWARD ILLUMINATOR. 163

illumination to die away. No w , again, good resol utions
can be obtained in the red similarly to those in the blue,
i. e., just at the point where the illumination begins to
decrease. It will now be quite time for those who have
never before used the instrument to look carefully to
the correction of the objective, and for the trial experi-
ment the object selected should be one that the observer
can master by the usual oblique illumination. It only
remains now to assure ourselves that the lamp is at the
proper distance from the stand, which is accomplished
by simply moving it farther away, or,_per co^ra, bring-
ing it nearer, sliding from right to left, and trying the
red and blue fields, as before instructed. The very best
position of the lamp as to distance is generally attested
by the general superior brilliancy of the illumination,
together with the fact that when this distance is just
right there will be room for greater lateral play of the
radiant without losing the illumination. Care should
be constantly observed to keep the lamp flame exactly
edgewise. It may be further stated that when things
are nearly in proper position, the smallest imaginable
movement of the lamp will often produce marked effects.

THE WOODWARD ILLUMINATOR.

For this novel and useful accessory microscopists are
indebted to Col. J. J. Woodward, of the U. S. Army.
A paper, giving a detailed account of the instrument,
by Col. Woodward, was read before the London Royal
Microscopical Society, and subsequently published in
the London Monthly Microscopical Journal. The paper

164 HOW TO SEE WITH THE MICROSCOPE.

is written with singular tact and perspicuity, and is here
reprinted unchanged :

A /Simple Devwefor the Illumination of Balsam-mounted
Objects for Examination with certain, Immersion Ob-
jectives whose "Balsam Angle" is 90° or upwards.
By Surgeon J. J. WOODWAKD, Brevet Lieut. Col. U.
S. Army.

[Taken as read before the ROYAL MICROSCOPICAL SOCIETY,

June 6, 1877.]

" Certain immersion objectives are so constructed that
they are capable of admitting rays which enter the front
lens at a greater angle with the optical axis than the
limit for dry objectives. That this is not only theoretic-
ally possible, but that such objectives have been success-
fully constructed, was several years since demonstrated
in the " Monthly Microscopical Journal" both by Mr.
Keith and myself,* notwithstanding which the contrary
lias often since been energetically asserted by writers in
the same Journal.

" Meanwhile, immersion lenses possessed of the exces-
sive angle in dispute, continue to be put into the market
by more than one maker; and perhaps some of the pur-
chasers will be interested in a simple device which I have
used for some time with such objectives to illuminate
test-objects mounted in balsam. This device consists
merely of a right-angled prism of crown glass mounted
beneath the stag-e in such a manner that its lon^ side

o o

can be connected by oil of cloves, or some similar fluid,

*June, 1873, p. 268; November, 1873, p. 210. March, 1874, p. 119; September.
1876, p. 134.

THE WOODWARD ILLUMINATOR. 167

with the slide on which the object is mounted. The
details of the plan will be understood by the diagram
on next page, in which the glass prism is seen in section
just beneath the object slide F F. Just below it is an-
other right-angled prism, of the same dimensions, made
of brass; the section of this prism is indicated by dark
shading in the diagram . The right-angles of both prisms
are truncated, and the facets are cemented together in
such a manner that the long sides of the prisms are par-
allel. The brass prism slips transversely in a groove in
the top of a holder, C, which is fitted into the sub-stage
of the microscope. D D is a blackened brass screen
held in position by two brass arms, one of which is
shown in the figure. This screen is parallel to the adja-
cent face of the glass prism, and has in it a small cir-
cular aperture, E, about the size of a large pin hole.
The side of the glass prism next the screen is covered
with black paper, in which is a corresponding pin hole.
The two pin holes are so placed that a beam of parallel
white sunlight (r) passing through both will be per-
pendicular to the sides of the glass prism on which it
impinges.

" To use this apparatus it is adjusted in the sub-stage
ot the microscope, a drop of oil of cloves is placed on
the upper face of the prism, the glass slide F F, on
which the object is mounted in Canada balsam under the
usual thin cover, Gr, is placed on the stage, and the sub-
stage is racked up until the drop of oil of cloves is
spread out into a thin layer, I.

" The object being thus arranged, it is evident that if

168 HOW TO SEE WITH THE MICROSCOPE.

a beam of parallel solar rays (white sunlight), reflected
from a plane mirror, be thrown through the two aper-
tures upon the face of the prism, being perpendicular
to that face, it will enter and pass through without
refraction until it reaches the upper surface of the thin
glass cover Gr. The parallel rays impinge upon this
surface, as is evident from the construction, at an angle
of 45° with the optical axis O O. If, now, the medium
next above the thin cover, Gr, be air, this obliquity will
be greater than the critical angle, and total reflection
of the rays will take place. If, however, the medium
next above the thin cover be water, the obliquity will
not be greater than the critical angle. Refraction hav-
ing taken place, the rays will enter the water, H ; and
if an immersion lens of sufficient angle of aperture be
focussed upon the objects mounted beneath the cover Gr,
these rays not merely enter the front of the objective, but
will form a well-defined image of the object on a brightly
illuminated field, which will be visible through the eye-
piece of the instrument in the usual way. Of course it
is evident from the diagram that with no dry objective,.
or any immersion objective of less than 90° balsam angle,
can anything whatever of balsam-mounted objects* thus
be seen.

" Immersion objectives may be divided according to
their behavior, with this apparatus, into three classes:
1st. Those with which, since they do not have sufficient
angle of aperture to admit the illuminating pencil,

* The apparatus can be used, of course, to secure black-ground illumina-
tion oi suitable dry objects if they are mounted on the slide instead of the
cover, as is usual.

THE WOODWARD ILLUMINATOR. 16 9

nothing can be seen, precisely as in the case of dry ob-
jectives. 2d. Those which have sufficient angle of aper-
ture to admit rays of this obliquity, but are incapable of
bringing them to an image-forming focus ; with these
the field appears well illuminated, but the objects are
not well defined. 3d. Those which not only admit rays
of this obliquity, but form well-defined images with
them. To this class belong not merely immersion ob-
jectives with the so-called duplex fronts, but others ;
and I may add, not merely objectives of American make,
but some constructed by a well-known English house-
As might be expected, the quality of the image formed
by the direct rays of the sun thrown through a pin hole
at this excessive obliquity varies very greatly in differ-
ent cases. I will state, however, that I have thus far
found at least seven objectives, some of English, others
of American make, which define sufficiently well under
these circumstances to resolve Amphipleura pellucida
mounted in Canada balsam. With the objectives which
performed best, the field was of exceeding whiteness
and brilliancy, but by no means dazzling, the frustule
undistorted, and the striae clean and black on the white
ground, very little color aberration being perceived.
With other objectives there was more ot less color aber-
ration and distortion, both which faults were in one or
two cases very conspicuous, although in the part of the
frustule most sharply focussed upon the striae svere
handsomely brought out. The objectives with which I
thus succeeded ranged all the way from one-fourth to
one-sixteenth immersion. I will add that the objectives

170 HOW-TO SEE WITH THE MICROSCOPE.

which resolved Amphipleura pellucida under these try-
ing circumstances, when used in the ordinary way with
this or other test-objects, displayed an exquisite perfec-
tion of definition which it would be hopeless to expect
to attain with objectives of less angular aperture.

"As it is no part of my purpose in this communication
to provoke ill-tempered discussion of the merits of indi-
vidual makers, I will not append a list of the results
obtained with the various immersion objectives I have
tried in this way. The apparatus can be constructed
for a few shillings, and those who take the trouble to
use it will soon see to which of the three classes any
particular objective they may test belongs."

Subsequent to the date of the reading of the preceed-
ing communication, Dr. Woodward proposed some slight
•changes in the form of his prism. Having had consid-
erable experience with the prism as now used, we append
the following description, and also the manner of work-
ing the instrument.

Essentially, it consists of a triangular prism of crown
glass. In the form adopted by Dr. Woodward the ob-
tuse angle is 98° and the two acute angles 41° each.

The prism may be used unmounted, by simply attach-
ing the same to the under surface of the slide containing
the objects to be examined, a drop of glycerine or oil
of cloves serving to secure optical contact, and at the
same time acting as cement to retain the prism in place.
Notwithstanding this is the arrangement employed by
many observers, it is but a faulty plan, in fact, a regular

THE WOODWARD ILLUMINATOR. 171

*' make-shift " arrangement. With the prism thus
mounted any movement of the object-slide will of course
cause a corresponding movement and decentering of
the prism; furthermore, such object-slides can only be
well examined when posed in nearly the horizontal
position on the stage; it often, too, occurs that the
intermediate drop looses its hold, suffering the prism to
slide or even to loose its attachment entirely; and then,,
again, I have frequently got the very best work when
the facet of the prism was slightly depressed from the
under surface of the slide.

It is far better, then, and for the reasons given, to
have the prism mounted, and to those who propose to
adopt my method of illumination, I will say that much
depends on the proper mounting, and that any piece of
sub-stage apparatus which shall impede the passage of
rays from the lamp to the mirror, or from the mirror
to the prism, will defeat the maximum working of the
latter. Hence, as a rule, it cannot be well mounted in
the usual sub-stage, the latter obstructing too much
light.

After much experiment, and with the hearty co-opera-
tion of Mr. Sidle, I am now in possession of the Wood-
ward prism, suitably mounted and adapted to the " his-
tological" of Mr. Zentmayer, as will be seen from
inspection of the cut on the following page.

This accessory, as above delineated in plan and sec-
tion, is easily placed in position on any of the histolo-
gical stands. Provision is also made for centering in a
lateral direction. The prism can also be revolved so as

172

HOW TO SEE WITH THE MICROSCOPE.

to use either angle. It can at will be raised or lowered^
or clamped in any desired position.

B

a. Vertical vi°w.

b. Sectional view.

c. Prism three-fourths full size.

In the adaptation of this useful accessory to the acme-
stand Mr. Sidle has been singularly fortunate.

This neat and compact little device screws, as I
have had occasion, on a previous page, to state, into the
well-hole of the acme stage. It is thus " on and off'*

THE WOODWARD ILLUMINATOR. 173

in a moment's time. All the necessary motions are pro-
vided for, and it may be depended on for first-class
performance.

From what has already been stated, it is almost need-
less to repeat that when either of the mountings de-
scribed are to be used on the histological or acme stands
the sub-stage must be removed. It is quite possible that
the mountings presented may, with slight modifications,
be fitted to other microscope stands.

The form of prism (angles 98°, 41° and 41°), as sug-
gested by Col. Woodward, will be found to do very
acceptable work. It occurred to me, after having had
considerable experience with this accessory, that there
was nothing gained by having the acute angles equal,
but on the other hand advantages would be insured by
an inequality of these angles, either of which might be
used as occasion required. I therefore begged Mr. Sidle
to make me a prism with an obtuse angle of 93°, one of
the acute angles to be 47°, the other to be 40°, and this
is the form I have adopted, believing it to be the most
seviceable arrangement yet proposed, and especially
adapted to the general run of modern wide-apertured
objectives. To provide one's self with two or more
forms of prisms will not involve serious expense. Either
of the mountings I have described can be modified so
that the prism can be removed and others substituted
in its place.

To use the Woodward prism — we will suppose on the
acme stand — first, screw the accessory into the well-
hole of the stage securely ; next, place the slide to be

174 HOW TO SEE WITH THE MICROSCOPE.

examined on the stage. With a one and one-half or
two-inch objective (having raised the prism so as to
contact nearly the under surface of the slide), focus
entirely through the body of the prism, so that its lower
edge may be seen in the field, and by turning the prism
in its mounting make this line, by estimation, as nearly
vertical as possible. If, perchance, this line appears to
the eye considerably to the right or left of the centre
of the field there is no harm done ; but you must make-
a note of the fact; this would indicate, however, that
either the stage is out of centre, or the mounting of
the prism has been injured.

Next, rack back the objective and remove the slide,
place a drop of glycerine on the top face of the prism ;
replace the slide and raise the prism so as to make con-
tact with its under surface. Having made this contact
exactly, depress the prism, say, about one-fiftieth of an
inch. Focus again with the low power, and bring the
lower edge truly vertical, as before instructed.

Remove the low power and substitute the wide-aper-
tured objective, and by way of illumination provide a,
small kerosene hand lamp, the flame of which ought not
to be higher than two-thirds the distance from the table
to the stage of the microscope; remove, also, the sub-
stage.

Now, if the lower edge of the prism was seen to the
right of the field place the lamp to the right of the
stage ; on the contrary, if the edge was seen to the left,
place the lamp to the left ; and in either case swing the

THE WOODWARD ILLUMINATOR. 175

mirror away from the lamp, placing it so that the gradu-
ating wheel shall read at about 34, 35 or 36 degrees.

The lamp being passed to the right or left of the stage,
as the case may be, and about four inches distant there-
from, bring the edge of the flame to the mirror; now
move the lamp to or from the front edge of the table,
so that the edge of the lamp frame, prism and centre of
mirror shall form approximately a straight line parallel
with the front edge of the table,

From the position described it will be seen that the
ordinary sub-stage would be entirely in the way ; hence
the necessity for its removal.

Making immersion contact, focus your objective, and,
without changing the position of the swing bar, manip-
ulate the mirror so that the field may be nicely ill und-
ated, select your object, which we take it for granted
will be <?ome difficult lined test.

Next, interpose the large bull's-eye condenser (flat
side to the lamp), thus concentrating light on the mir-
ror ; adjust the object glass.

It will be well .now to try the effect of various degrees
of obliquity, remembering that any considerable move-
ment of the swing- bar will necessitate a new adjustment
ot the condenser. A slight change, too, in the position
of the lamp will sometimes be attended with excellent
results, keeping, in all cases, however, its edge to the
mirror.

The above includes the author's method of working
the Woodward prism ; but as this accessory bids fair to
come into general use he will now traverse the ground

176 HOW TO SEE WITH THE MICROSCOPE.

over again, feeling sure that many there are who will
not object to some further discussion of the subject.

In the initial attempt to use the prism, the observer
should select an object (balsam mounted) with which
he is tolerably familiar. The collar adjustment, also,
should have been previously ascertained. The next step
is to decide on the proper position of the radial bar, i. e.,
its distance from axis, the extent of this distance will
be demonstrated by the illumination becoming too feeble,
the images, also, becoming generally unsatisfactory. The ,
remedy is, in such cases, to cause the radial bar to approach
nearer to an axial position, until the field can be suffi-
ciently lighted and the object displayed with tolerable
vigor. Thus the operator has the means of " gauging "
his objective. The mirror being properly posed, it re-
mains to obtain the best possible illumination, which is
effected by slight changes of the mirror, condenser, and
finally the lamp. When things are generally about
right, a little movement of the lamp (grasping it firmly
by the bowl), sometimes twisting it to the right or left,
so as to get the flame exactly edgewise to the mirror
(which is best determined in this way), will result in
very nice effects, bringing out the striae on such tests as
the Moller test-pla,te in a very satisfactory style.

Resolutions of difficult test objects are accomplished
with this illuminator in a very handsome manner. It
is an easy instrument to use, and will adapt itself kindly
to the objective, of course; the higher the balsam
angle of the object glass, the better the definition. It
has, in its ease of adaptation a decided advantage over

THE WOODWARD ILLUMINATOR. 177

the Wenham forms, and in the comparative examina-
tion of objectives, the wedge illuminator is an exceed-
ingly handy accessory. In the determination of the
collar adjustment corresponding to the point of maximum
aperture, the same holds true.

We have spent two or three entire evenings in the at-
tempt to determine which of the two illuminators is the
most effective ; and our experience leads to the conclusion
that the " reflex " is somewhat the superior instrument
in the resolution of the most difficult lined tests; never-
theless, we are glad to give the newcomer a place in the
accessory box, and expect to make it very useful. It is
easily made and mounted, and ought not to be expensive.

Another matter closely allied to the new illuminator
may as well be mentioned here. Learning that the
Messrs. Spencers had just completed a new one-fourth
inch objective, which was to be sent to the Paris Expos-
ition, we wrote to these gentlemen asking the loan of
the glass for examination, the Messrs. Spencers re-
sponded promptly, and it occurred that we received
the one-fourth and the new illuminator the same day.
We were thus enabled to put the illuminator to practi-
cal use at once, in this manner: First, we took our one-
sixth, working it with the illuminator over the No. 20
of the Moller plate getting the radial bar as far from
axis as the objective would allow and preserve a good
display of the striae. This done, we substituted the
one-fourth in place of the one-sixth, keeping the illum-
ination, etc., carefully in the same position, (the cover
of the plate was as well adapted to the one glass as the

178 HOW TO SEE WITH THE MICROSCOPE.

other.) We found at once, that in order to obtain suf-
ficient light, and retain the general vigor of the image,
it was necessary to approach the radial bar to the axis
and the required movement of the latter was quite per-
ceptible. It was therefore accepted that the one-sixth
had the higher balsam angle. The question then turned,
-as a matter of course, on the respective working dis-
tances; that of the one-sixth was known. It remained,
therefore, simply to measure that of the one-fourth,
resulting as follows : The working distance of the one-
sixth is twenty-four-thousandths of an inch; while that
of the one-fourth was found to be thirty-two-thou-
saudths of an inch, a difference of 33 per cent in favor
of the one-fourth. Thus it will be seen that in this
instance the question as to superiority may be further
taken under advisement. We relate this bit of " prac-
tice" with the illuminator in illustration of the pre-
ceding remarks.

One thing was proven even by the above experiment,
to wit: Having our tenth on hand, held in reserve for
especial demands, we would greatly prefer the one-
fourth as an intermediate oflass. This fact is too obvious
to need further comment, and, in general, we are glad to
add that the new one-fourth of the Messrs. Spencer is
indeed a lovely glass, and if properly exhibited in Paris,
will be an honor to the talented makers.

The modified illuminator above described (obtuse
angle, 98°, acute angles, 41° each) will work very well
with objectives having wide air apertures only; hence,
like the modified " reflex," it will work over dry mounts,

THE WOODWARD ILLUMINATOR. 179

in such cases, in common with the modified " reflex,"
its action, to some extent, is crippled; nevertheless,
nice resolutions are to be obtained with either instru-
ment, with either of which we are able to instantly
display the transverse stride of amphipleura pellucida,
frustulia saxonica, etc. The simplicity of Dr. Wood-
ward's device, its ease of working, and the facility it
affords for the comparison of objectives are in them-
selves strong points in its favor, and to these may be
added the satisfactory character of the resolutions ob-
tained. We gladly accord to Dr. Woodward our appre-
ciation of the value of his illuminator.

We are informed by General Cox that the pin hole
apertures are only used when working with sunlight
illumination ; they also serve a useful purpose as an assist-
ance in measuring with greater precision the obliquity
of the illuminating pencils employed, thus enhancing
the value and capacity of the instrument.

TOLLES' TRAVERSE LENS.

It now remains to present to the reader the Tra-
verse Lens, devised by Mr. R. B. Tolles. The follow-
ing is the inventor's own description of this valuable
accessory, and is taken from the American Journal of
Microscopy :

"With the advent of objectives of jncreased interior
angle aperture, the indispensableness of equivalent ac-
cessory means for the illumination of the object became
immediately evident.*

* See"M. M. J.," July, 1871, p. 38.

180 HOW TO SEE AV1TH THE MICROSCOPE.

"In my first construction of such object-glasses I
therefore required to provide means which proved so
suitable that I have adhered to their use to the present
time.

"The first appliance was a deep plano-convex lens, cen-
trally mounted below the object, and having- its centre
of curvature in the object place. Afterwards I adopted
a plano-cylindrically convex lens, equal to a hemisphere
less the thicknsss of the object-slide, which was placed
in immersion contact with the base of the slide, so that
the object itself formed the centre of curvature of this
illuminating lens. Around the convex surface of this
central lens moved a shutter to regulate and limit the
access of light, and it was provided also with a small
plano-concave lens which, applied by its concave to the
convex surface of the larger lens by immersion contact,
cancelled the refracting surfaces and allowed a perpen-
dicular beam of light to reach the suitably immersed
object without refraction.*

" The device in a more complete form is represented in
the annexed figure, where P is the basilar plate of the
whole traverse system, having a circular groove and
track in which the carriage, C, moves. On a projecting
arm, A, of the carriage, C, are mounted whatever ap-
pliances are to be used to modify or direct the light upon
the traverse lensf T, in the direction of the object at
the centre of the system.

" In the figure, the concave lens, N, is shown in posi-
tion on the arm. Thus situated, the interior convex

* M. M. J., May, 1873, p. 213.

TOLLES' TRAVERSE LENS. 181

and concave surfaces being of no effect, the two exterior
plane surfaces of the traverse system constitute it a prism,
and every slightest movement of this concave facet lens
on the traverse lens, T, would give a different prism to
infinite variety. In this arrangement the concave mir-
ror can be used in the ordinary manner and condense
light enough upon the object for all ordinary purposes.
The full interior aperture of a dry objective would be
reached at the very convenient obliquity of 41°; ^. e.,
at less than the critical angle, or angle of total internal
reflection between crown-glass and air. L is a double
convex condensing lens, that may be placed at about its
principal focal distance from the object.

" For a condenser, with the size of apparatus as drawn
in the figure, a simple lens of 1J inch focus, and about
ten (10°) degrees of aperture, is convenient, and if the
lens is movable along the arm, A, ^it can be focussed
readily on the object, the position being fixed by inspec-
tion. This would be well for parallel rays. If diverg-
ing rays are used another lens of two or three inches
focus, mounted on the arm, A, will conveniently take

182 HOW TO SEE WITH THE MICKOSCOPE.

up the rays from the radiant at the distance of the focus
of this supplementary lens.

" The plate, P, is graduated on its circular edge, as in
the figure, to two degrees, and the arm, A, has a swing
of seventy degrees of arc each way from the axis of the
microscope. An index-line is marked on the bevelled
edge of the carriage 10° from the axis of the condenser,
which must be added to or subtracted from the real ob-
liquity of the illuminating rays.

" It is obvious that any observation made and duly re-
corded as to its conditions, as of obliquity of incidence
of illuminating pencil or ray, form of the pencil or beam,
focal length and distance of the condenser, such obser-
vation could be successfully repeated. The record of
the obliquity of the most oblique rays reaching the ob-
ject directly, and giving view of it at the eye-piece with
luminous field, would express the ' balsam ' aperture,
or more correctly, the half interior aperture of the ob-
jective when the front lens of the objective and the
traverse system are of glass of similar refraction.

" Having thus the ' b&lsam ' angle, we readily calcu-
late or learn the corresponding angle for glycerine,
or water, or any medium of which we have the index
of refraction. A corresponding notation, perhaps for
air, might be engraved in juxtaposition on the basilar
plate."

CHAPTER V.

ILLUMINATION.

Ordinary daylight is the cheapest; and for a great
many purposes the microscopist will find it amply suffi-
cient. It will be found a great convenience to have the
light enter the room considerably to the left of the
microscope, in which case we naturally adjust the mirror
with the right hand. Placing the instrument directly
before the window is objectionable, and such a position
should be avoided if possible. The quality, as well as
the quantity of daylight illumination will, as a matter of
course, vary with the particular aspect of the day. In
bright sunny weather the light from a white cloud, as
has often been recommended, is pure and pleasant to
work with, and can be used with tolerably high ampli-
fications with good success. In cloudy, rainy weather
it is still quite possible to work with powers up to, say
200 diameters. The recent introduction of the swing-
ing- sub-stage has worked somewhat of a revolution in

O O

our own practice. For years we have steadily eschewed
the achromatic condenser as being a costly and incon-
venient affair, making more " bother" than it was worth.
The principal objection I had to urge against its use was
that it was a fixture beneath the stage, thus preventing
me from varying the obliquity of the illumination at
will, as I desired, and, as a rule, practically I got better

183

184 HOW TO SEE WITH THE MICROSCOPE.

effects without than with it. The former condensers
Avere generally of short focal length, and of consider-
able aperture. In the late ^tands having swing sub-
stages, it being possible to swing sub-stage and con-
denser together bodily, there seems to be no further use
for condensers of wide angles, while on the other hand
one is enabled to use in the place thereof cheaper and
much less expensive instruments, and the lower the
angle the better, and one need not be very particular
as to the matter of achromatism.

On commencing the use of the little Histological, it
occurred to the author (and probably to scores of others)
that its swinging stage was a strong invitation to experi-
ment again with sub-stage condensers, not for the pur-
pose of resolving difficult tests by extremely oblique
illumination, for in this work the achromatic condenser
is of no manner of account, but, per contra, it seemed
obvious that by the use of a narrow apertured lens
placed below the stage, and so arranged that its inclina-
tion might be changed at will, good effects might be
secured in two directions : First, by the concentration
of a narrow cone of light immediately upon the partic-
ular portion of the object under examination, thus en-
abling the observer to sharply illuminate a certain point
of his object, and with less danger of drowning out
details in a general flood of light. Secondly, such a
contrivance would do good service by daylight in dark
and rainy weather. It required but few experiments to
demonstrate that there was force in the above reasoning,
and the next thing in course was to ascertain what par-

ILLUMINATION. 185

ticular form of condenser would be the best adapted for
the purpose.

In determining how far it would be practicable to cut
•down the angle of the condenser, thus reducing the
illuminating cone of light, we have made countless ex-
periments, while the IOAV stage of the Histological ren-
dered it imperative that the focal length of the lens
should be such as would best accommodate the little
stand. To sum up all these trials, we find that the
cheapest inch objective mac!e by Mr. G-uncllach, or the
inch of the Messrs. Beck's " National Series," are, either
of them, well adapted for the purpose. Mr. Gundlach's
inch has a rubber front which can be removed, while
the setting of the Beck " National " is extremely short,
and thus suited in this respect for the purpose.

This, then, is the author's arrangement for work with
low or moderate powers by daylight illumination, and
the condenser described has become almost a fixture.
In the darkest clays there will be plenty of light, using
the concave mirror, while in bright, sunny days the
plane can be substituted. The general amount of illu-
mination can be changed at will by merely raising or
lowering the sub-stage, and the nicest effects in the way
of definition obtained. The swing-bar can also be
placed so as to afford central illumination, or it may
(condenser and all) be swung laterally up, say to an
angle of 40 or 50 degrees from the axis; and it further
remains to say that either of these cheap objectives are
real good, honest glasses for the money.

186 HOW TO SEE WITH THE MICROSCOPE.

SUNLIGHT.

In the study of very minute and delicate structures
requiring the utmost separating or resolving- power of
the objective, remarkable effects are to be secured by
condensing sunlight on top of the object by means of
the concave mirror, the object being mounted with a
cover in the usual way. The objective used should of
course have wide aperture. The mirror being posed
slightly above the level of the stage, the sunlight is
thrown on the surface of the cover, and making a very
acute angle therewith. Although not absolutely neces-
sary for this purpose, those stands furnished with swing-
ing sub-stages, allowing the mirror to rise above the
level of the stage, are extremely handy and convenient.
By the employment of this illumination in conjunction
with object-glasses of wide angles, the most difficult
diatoms, such as amphipleurapellucida^frustulia saxonica+
etc., are easily and forcibly displayed. The advantages
attending the use of monochromatic sunlight, as ob-
tained by the intervention of the cupro-ammonia cell,
or a plate of blue glass, have long been known. Thi&
illumination is procured most easily as follows: Cut
with a diamond, or the point of a file, a small piece of
the blue glass roughly to fit the cap of the eye-piece,
so that when the cap is restored to its place the blue
glass shall be between the eye and the eye-lens of the
eye-piece, and the light is thus modified before it reaches-
the eye. This is the handiest method of obtaining mo-

ARTIFICIAL LIGHT. 187

nochromatic illumination we have ever tried, and the
resolutions are quite as strong and effective as when the
cupro-ammonia cell is used in the usual manner. In
working with sunlight by either of the methods de-
scribed, care should be taken to exclude the full strength
of the solar beam ; that is, if the sun be clear and bright.
Too much light, supposing the manipulations are tolera-
bly well attended to, will be manifest by the appearance
of a multitude of diffraction lines, and these as a rule
may be recognized by their extending beyond the ob-
ject observed. Under very high amplifications, involv-
ing the use of powerful eye-pieces, we can of course
help ourselves to a little more of the solar beam. When
the sun is very clear, the beam being condensed on the
top of the cover, as above described, there is danger
sometimes, if the object be balsam mounted, of the heat
starting the balsam. In this way we once ruined a
Moller probbe plate. A very little attention will, how-
ever, provide against accidents of this nature.

ARTIFICIAL LIGHT.

For the ordinary purposes of the microscopist the St.
Germain or German Student's Lamp, 0. A. Kleemann's
patent, or a similar lamp made by the Cleveland Com-
pany, will be found quite satisfactory. This style of
lamp is too well known to require any extended descrip-
tion. The flame is bright, clear and intense, and its
height can be changed at will. It is easily kept in
order, and has the advantage, too, of being well adapted
for ordinary household purposes. The breakage of

188 HOW TO SEE WITH THE MICROSCOPE.

chimneys has been a serious objection to its use ; a brand
of chimney known in Cleveland as the " Crown" (each
•chimney having a crown ground in the glass) seem to
be very free from breakage. Non-combustible wicks
are to be obtained, fitting the K Iceman lamp. These
are clean and handy, obviating the necessity of occa-
sional cutting and trimming; but to our mind the light
is not so intense, and therefore we prefer to use the old
style of wick. These lamps burn very steadily, and are
not easily affected by occasional drafts, and this is a strong
recommendation in their favor, as is also the ease with
which they are kept in order. For investigations of
exceedingly difficult objects the circular wick is not so
well adapted, and recourse must be had to lamps carry-
ing flat wicks. The best lamp we know of, of the lat-
ter style is the Mechanical Lamp, manufactured in New
York City. The lamp stands about ten inches in height.
The height cannot be changed, and this is an objection.
It burns kerosene oil, without any chimney. The body
contains a movement which, on being wound like a clock,
drives a blast wheel, and thus supplies a current of air
at the point of combustion. Although there is a peri-
odicity noticeable in the burning of this lamp, never-
theless the flame is very steady, is very intense, and
superior to gas. Like the St. Germain, this lamp is
very handy to have in the house, and it takes but little
trouble to keep it in order. The movement should be
•cleaned once a year, and any one possessed of fair me-
chanical skill will be competent to do this. While
burning, the clock-work makes scarcely any noise. An-

ARTIFICIAL LIGHT.

other form of this lamp has the movement placed in the
case flatwise, thus allowing the flame to burn within
three or four inches of the table. The lamp is thus ren-
dered very handy for use when direct light is wanted.

The author has found, as a result of thousands of ex-
periments, that the very best artificial light for the pur-
pose of the microscopist is only to be had from a small
but very intense flame. The smaller the flame the better,,
owing to the fact that there is less light diffused. We
therefore use and strongly recommend the smallest ker-
osene hand-lamp procurable, and fitted with a well-be-
haved burner of the smallest capacity. If possible let
the lamp bowl be so low that the flame will be, say three
or four inehes only above the table, thus adapting the
lamp for use by direct light. On other occasions the
lamp can be supported in a more elevated position.
With a little lamp of this description, in proper order r
all the most difficult tests known to the microscopist
can be well displayed, provided^ obviously, that the ob-
jective, etc., shall be competent for the work. It is of
importance, when any lamp provided with a chimney is
to be used, that the latter be kept scrupulously clean,
especially from a whitish film that forms on the interior.
A chimney may appear to be perfectly clean while cold,
but when heated the aforesaid film can be detected, and
should be removed, if delicate observations are in hand,
in which case it will be well, too, if the wick be three
or four weeks old, to remove the same and substitute a
fresh one. Even in the case of the small pattern of
lamp recommended there will be no occasion to force

1(JO HOW TO SEE WITH THE MICROSCOPE.

the combustion to the fullest extent such a burner will
.afford. A flame with the lamp burning at one-half its
capacity will be amply sufficient, and even this would
be too much for the proper display of some of the most
-difficult tests.

Attempts have been made to modify artificial illumina-
tion by the introduction of blue tinted chimneys, white
, ground illuminators, etc. We have patiently tried the
entire list, and reject them all, from the fact that there
is no real advantage secured by their adoption which
•cannot be obtained in a simpler way without them.
The neutral tint " Light Moderator," so called, is a
pleasant thing enough for use with moderate amplifi-
cations; yet there is nothing seen with it that cannot
be as well shown without it.

The blue tinted chimney cuts down seriously the in-
tensity of the lamp illumination to an extent which will
defeat the resolution of any severe test, while, on the
contrary, any and all work with the lower powers can
be as well accomplished without its aid.

The reader has thus before him all the various kinds
of illumination we use. A great deal of the profes-
sional routine of work not requiring, as a rule, the em-
ployment of the highest amplifications (such as the
'examination of urinary deposits, malignant growths,
etc.,) we try as far as possible to accomplish in the day
time, and by the use of diffused daylight. If the sun
happen to shine, and it be desirable to cross-question
some preliminary examination under the highest pow-
ers, we generally use the sunlight condensed on the top

ARTIFICIAL LIGHT. 191

of the cover, or perhaps v/ith the aid of the bit of blue
glass in eye-piece. For work at night we employ at
times all the lamps we have described. Should the
routine examinations be prolonged into the evening, we
use the German student's lamp for preliminary work,
the same as we use diffused daylight in the day time.
But should the higher amplifications become necessary,
we bring the mechanical or the little hand-lamp into
play. The German student's will still do service in the
lighting up generally of the work-table at intervals.
For the showing of such objects as the Nos. 18, 19, and
20 of the Moller plate by lamplight, of course the little
hand-lamp, or the lower model mechanical is impera-
tively employed, especially when the Wenham " reflex "
illuminator is selected.

There remains yet another method of sunlight illumina-
tion which will be found useful at times. I refer to the
use of the "reflex" illuminator with direct sun-light.
In this case the solar beam can be received through a

o

olosed window (quite a boon in the winter season) and
reflected from the plane mirror. This illumination is
only suitable for work with wide apertures, and ever
the most minute objects, and the mount must be free
from surrounding objects of a coarse character, else,
from the extremely oblique character of the illumina-
tion these stronger and coarser objects will project their
stroiig shadows across the field, causing nothing but
contusion and chaos. With the genuine form of the
Wenham " reflex " an epithelial scale would hardly be
recognized were there several in the field. The princi-

192 HOW TO SEE WITH THE MICROSCOPE.

pal advantage in the use of the " reflex" with sunlight
is in arriving at a knowledge of surface markings, and
for this purpose it is indeed very valuable. Thus work-
ing the " reflex " by sunlight, the mirror must be manip-
ulated so as to produce the same effects as have been
described by moving the hand-lamp and conversely.
The mirror may be substituted for the hand-lamp when
working in the evening, but the most favorable results-
are obtained with the light direct. This reflex and sun-
light illumination is especially desirable when one wishes
to trace out structure situated in one particular plane,
to the exclusion of that lying in adjacent planes. In
the general squabble to produce the so-called penetra-
tion, this very important item has been lost sight of.

We are now ready to consider a matter which has
been alluded to on a preceding page. It has been
already stated that the maximum performance of ad-
justable objectives can only be secured when such object-
glasses are worked at the point of their maximum aper-
ture, and that this point is by no means a fixture but
varies with different objectives. Every observer should
then ascertain for himself as to the proper handling of
his object-glasses in this particular. Methods will now
be given which, although but approximate, are suffi-
ciently precise for the use of the practical manipulator.

For the purpose of testing the point of maximum
aperture for object-glasses having apertures, say from
40° to 175°, proceed thus: Place the objective in posi-
tion on any good stand having a thin stage and mirror
attached to radial arm. Commence by focussing any

ARTIFICIAL LIGHT.

suitable object on the stage, with the mirror in a central
position, the collar of the objective being- set at the ex-
tremity of its range. Now, by degrees, swing the radial
bar carrying the mirror, meanwhile adjusting the mirror
so as to secure all the illumination possible, just as would
occur in arranging for greater obliquity of illumination,
until the obliquity of the light becomes as great as the
objective will bear; i. e., until the greatest degree of
obliquity has been obtained that will secure a tolerably
well-lighted field. Now move the radial bar a little,
and but a little further from axis, meeting this change
by the proper manipulation of the mirror, and so as •
still to secure all possible light. The object now ought
not to have more than one-fourth the usual illumination,
but should nevertheless be distinctly seen. Next, revolve
the collar and notice the effect. If you get less and less
light as the collar is turned towards the other extremity ,.
of its range, it would show that it was already at the "
point of its maximum aperture ; on the contrary, should \
you get more light, it will be apparent that the aper-
ture increases as the collar is turned, and thus turning
the collar by degrees, move also the radial bar still fur-\
ther from axis, manipulating the mirror as before, and ^
to the same end, and so proceed as long as the change,
of the collar gives more light. You have then, by^
simple inspection of the position of the adjustment, af
tolerable idea where the maximum of the objective is to j
be found. Note this : Now remove the object, place there
stand in a horizontal position, and, without changing'
the adjustment of the objective, proceed to measure its,

13 'Microscopy.

to

1C

194 HOW TO SEE WITH THE MICROSCOPE.

angle by the method previously given. Note again the
.angle obtained. Next, change the collar adjustment a
-division or two, and again measure the aperture. Com-
paring results, it will become obvious which of these
two positions of the collar corresponded to the larger
.•angle. Should the latter measure prove the least, it
will be necessaiy to reverse the movement of the col-
lar, placing it a division or two from the previous posi-
tion but in the reverse direction, and by a few measures
•of this kind, which, by the way, are quickly accom-
plished, the point in the collar adjustment correspond-
ing to the maximum aperture on the glass will be ascer-
tained with considerable precision. In the method just
•described the primary object was to get an approximate
idea as to the point of largest aperture, and with the
least outlay of time, and subsequently, by actual trial,
to arrive at a more precise determination. The whole
process involves but little outlay of time, ten minutes
being quite sufficient for the purpose.

With objectives of high balsam angles it will be neces-
sary to employ the genuine Wenham " reflex " illumina-
tor (angle of facet 26°). With this instrument proceed
as has already been advised until, by the lateral move-
ment of the lamp at either the extremes, right or left,
the illumination commences to die away, the field being
blue or red, according to the position of the lamp. It
will generally be a saving of time to start with the
collar of the objective at "closed." Having found the
best position for the lamp, as we have before directed,
move it still a little further laterally until the field of

ARTIFICIAL LIGHT. 195

the instrument shall only be illuminated sufficiently
to enable you to see your object distinctly. Now,
keeping things thus, revolve the collar, and notice the
effect on the illumination, and thus, as in the case
already presented, you have the means of judging- as
to the aperture of the objective. And as an example
I now relate a bit of experience not twenty-four hours
old : We have just had in hand an objective claiming to
have high balsam angle, and we desire to know some-
thing about it. First, we look to its working distance
and find that it will work through covers one-fiftieth of
an inch thick, its distance is therefore ample. Applying
the Wenham " reflex " we test as to aperture, and pre-
cisely as has been above described, thereby learning
that its greatest angle occurs when the systems are at
" closed." We find, too, that as the collar is revolved
towards the " open point," the angle goes down rapidly.
We therefore conclude that to work this glass at. its
maximum performance it will be necessary to use covers
thick enough to cause the objective to " correct" at or
near " closed.'' It will take but a moment to try the
actual experiment, aud to see if theory holds good in
practice. For this purpose we place the " reflex " in
position and the No. 20 of the balsam Moller plate on
the stage, making immersion contact with water. Next,
we attempt the resolution of the shell, and with the
best manipulations at our command succeed in getting
but a tolerable show of the striae. I have the blue field
in hand, with the lamp at the extremest point to the
left: the best display being thus obtained, as the lamp

196 HOW TO SEE WITH THE MICROSCOPE.

was thus shoved to the left the definition was improved,
but we were compelled to desist from this movement
owing to the loss of light, and were therefore content
with the lamp as far to the left as was possible without
sacrifice of the illumination. Of course the objective
was adjusted with all possible care, the collar standing
within three divisions from " open point."

We now carefully raise the objective, and removing
the water with a bit of blotting paper, we substitute a
drop of glycerine, focussing and adjusting the glass
again with the glycerine intermedium ; the glass now ad-
justs at nearly closed, the collar having made nearly two
full revolutions from its former position. It is further
obvious that we have now more light generally; we
can, too, move the lamp to a greater distance right or
left without loss of illumination. In fact, things in
the tube have a sunshine appearance that is very accept-
able. We now attempt again the resolution of the
same shell, using the blue field as before. Finding that
the lamp will bear to be shoved further to the left than
before. And now, even before arriving at the limit of
light, i. e., the lamp not so far to the left as we might
place it, we are rewarded by a splendid display of the
transverse striae, this, too, with illumination, I was
going to say in excess, at all events enough to allow the
use of the one-halt and the one-fourth solid eye-pieces.

We have thus described this experience taken from
our private practice, giving the actual results obtained.
Well, now, suppose that with the Wenham reflex the
experiment had turned out a total failure; i. e., that we

ARTIFICIAL LIGHT. 197

could get no light through the objective, showing that
in this case the accessory was a reflex and no mistake;
or, suppose that our best efforts were only rewarded by
a dim view of the diatom seen doubled up endwise amid
a plexus of indeterminate undefinable diffraction lines,
the entire field miserably illuminated, of a muggy,
smoky, dingy yellow, as if a piece of yellow flannel
had been used in place of the lamp, and that we could
only get this much in just one solitary position of the
lamp ; then the experiment is quite as interesting, quite
as valuable, and if made in due time will amply repay
its cost.

As a matter of course, the lower the balsam aperture
the lower will be the grade of its work with the u re-
flex ;" nevertheless, the point of maximum performance
can be ascertained by the method above given, and in
the testing of object-glasses I make it a point to look
after the balsam angle and the point of maximum aper-
ture at the same sitting, the only additional trouble
involved being the change in the thickness of cover, or,
as in the instance named, substituting glycerine in place
of water.

We have entered into these details, feeling assured
that the facts are worth knowing, and that many there
be who have not given these things due attention. Of
those who have visited us, eight out of ten saw the work-
ing of the " reflex " lor the first time, while without
exception all have seemed greatly pleased and interested
with such comparative experiments as we have just de-
scribed. Let the reader rest a moment here and I will
relate a little incident :

198 HOW TO SEE WITH THE MICROSCOPE.

Not long since I was honored with a call from a gen-
tleman who had put himself to some little trouble in
visiting Cleveland. Said he: "I have been for some
time desirous of visiting you ; I have read all your ar-
ticles in the journals, and have been permitted to read
your letters to our mutual friend, - —.1 want

to know something more about the " balsam angle "
business; ditto, about the " 180°"; I confess these ex-
treme apertures seem to me "impossible"; and then,
again, we have high authority that the true aperture of
any object-glass cannot exceed 120° and the assertion is
fortified with reasoning that I cannot well dodge. I
have brought with me an excellent glass purporting to
have corrected angle up to 140°, and would like to have
some comparisons made with your own. I am after the
facts, and have no personal bias in any direction," etc.,
etc. He also went on to state that Mr. Wenham had
expressly asserted that direct light could be obtained
with the " reflex." At his suggestion I showed him
the No. 18 of the balsam Moller probbe plate illumina-
ted with the genuine " reflex." The field was brilliantly
lighted with just enough of the blue in to take off' the
intensity of the glare. The shell appeared without sen-
sible distortion, edges sharp and clean, and with a full
stand of lines from end to end. Revolving the stage so
as to place the saxonica in a diagonal position, we had
little difficulty in obtaining simultaneous views of both
transverse and longitudinal striae, thus cutting the valve
into checks or squares. The same little hand-lamp was
used, and we had nice shows with eye-pieces up to the
one-fourth inch.

ARTIFICIAL LIGHT. 199

My visitor was delighted, nor did he attempt to con-
ceal his delight. " Now," said he, "just keep all things
just as they are, but take off your glass and put on
mine." The same was accordingly done, and the result
was that we could not see the diatom at all, nor could
we, by the best possible manipulation of the lamp, see
it well enough to recognize it. I suggested the possi-
bility that the glass might not be truly centered, and
thus to some extent be defeated. Attention was there-
fore given to this, but without avail. My friend's ob-
jective positively refused to have anything to do with
the reflex illuminator.

Now, I have found, by countless experiments, that of
two objectives, the one working well with the genuine
"reflex," and another refusing to so work at all, the
former will be far the superior glass for any and all
work; a fact which, after a little subsequent experi-
ment my visitor was not slow to accept. I am of course
referring to objectives generally known under the ap-
pellation of " high powers."

Thus it will be seen that the Wcnham " reflex " is for
any of these purposes quite a handy and effective little
instrument, and ought to have its place in the accessory
box of every microscopist. It will serve, too, in its
legitimate capacity as designed by its inventor, i. e,, as
a k< dark ground illuminator;" but herein will be found
itb least value. To return directly to our subject: I
cannot too strongly recommend that every one inter-
ested in microscopical work requiring the employment
of high amplifications with fine defining power, should

200 HOW TO SEE WITH THE MICROSCOPE.

study their objectives, and if for the sake of practice
only, those of their friends to which they can have
access. There is no time lost in this occupation ; on
the other hand, it will usually result in economy of
time. For instance, if your glass totally refuses to asso-
ciate with the genuine " reflex," you are hereby informed
that such a glass is totally unfit for any such purpose
as resolving the last numbers of the Moller probbe plate,
or for any kind of duty requiring the recognition of
lines as close as 80,000 to the inch. Thus, by the method
described you can, in less than ten or fifteen minutes
time, settle definitely any such question as to the capacity
of your object-glass.

This matter is suggestive, and with the reader's per-
mission I desire to " switch off on a side track " again,
for we have " an ax to grind." We often, yea, almost
every day, hear those who regard the study of objectives
as one worth attention, roundly condemned by workers
in natural history, biology, etc. The former are said to
be " only diatom crackers," wlio do nothing but fool
away their time over difficult diatoms, and are said to
have angular aperture " on the brain." Now, reader,
when you shall be permitted to peep behind the curtain
as often as I have had the chance in the past (which, by
the way, I have improved), you will find that the very
gentlemen who make all this hue and cry are the very
ones who have been and still are " fooling away" their
time. You will find, as a rule, that each and every one
of them have their little cabinet of " difficult tests,"
over which they spend (sub rosa) night after night in

ARTIFICIAL LIGHT. 201

an absurd attempt to display the hateful markings ; an
attempt, too, as futile and puny as that of the child who
cries for a piece of the moon. And why? Simply be-
cause the object-glass employed is not suited to the work
in hand. Nor is the picture overdrawn, as more than
one lady can attest, or the " looker on in Venice"
vouch for.

To all such, to all who value the microscope as an aid
to scientific investigation, let me urge the importance
of studying well the nature, capacity and capabilities
of the objective, and to this end, and in the special line
we have been discussing, the Wenham " reflex" will
prove itself a valuable and important accessory, and a
time saver of the very first water.

CHAPTER VI.

CHOICE OF OBJECTIVES FOR REGULAR WORK.

Practically, for the past four years, we have confined
ourselves to the use of four object-glasses, namely, an
inch or two-thirds inch of 45° or 50°. A one-half inch
of 38°. A one-sixth immersion, balsam angle ranging
from, say 87° to 95°, according to the position of its-
collar, and a one-tenth immersion having a constant
angle of 100°. Of the last two glasses, the one- sixth
has a working distance of one-fiftieth of an inch. The
one-tenth will work readily through covers one-one-
hundredth of an inch thick.

The orthodox theory has been, and I suppose still is,
that each worker ought to select his stand, objectives,
accessories, etc., with special reference to the particular
line of investigations he may elect to pursue; and since,
as before intimated, there may be more or less force
attached to such a platform, I neither accept it nor reject
it; nor am I " on the fence," halting between two con-
flicting opinions. Without going into any special dis-
cussion of thdpros or cons, we will proceed to state the
character of the work in which we have been engaged,
accompanied with a recital of the special methods, etc.,
employed.

First, we use the microscope constantly from January
to December in examination of urinary deposits, and
for the study and detection of malignant growths. In

CHOICE OF OBJECTIVES FOR REGULAR WORK. 203

conjunction therewith the aid of medical chemistry is
constantly sought, especially in the diagnosis of renal
diseases. Work of this description is continually on
the tapis " all the year round." In addition to this we
use the instrument as a necessary aid in our daily lec-
tures, and for the private instruction of students at the
college on matters pertaining to our Chair of Histology
and Microscopy. Besides these duties we have more or
less private instruction entirely outside of the college
to attend to. The range of work then to be accom-
plished is by no means a narrow one, and anything in
the way of instrumentation that would assist either
teacher or pupil will find at all times in my laboratory
a ready market.

We thus state the character of the work we have in
hand, and also the instrumentation employed for its ac-
complishment; perhaps a leaf or two from our daily
practice may prove acceptable, and with this hope we
proceed :

We have said that a large amount of our work is
over urinary deposits. For this purpose we use the
" histological " stand of Mr. Zentmayer, the tube short
and the stage level. Nine physicians out of ten engaged
in similar examinations use their instruments in an in-
clined position, covering their preliminary mounts,
absorbing the superfluous moisture with a bit of blot-
ting paper, employing, too, an objective as high as the
one-fourth, or perhaps higher. Now nine-tenths of all
work of this description can be accomplished with a wide
angled inch or two-thirds, and by keeping the tube short

204 HOW TO SEE WITH THE MICROSCOPE.

and the stage level there will be found, in ninety-live
cases out of the hundred no necessity for covering the
mount. I simply place on a clean glass slide a drop of
the specimen to be examined and, without covering it at
all, place the same on the stage, the spring clips being
turned back out of the way, for even these are a draw-
back to rapid work. It will be often necessary to use
re-agents, and to this end the long working distance
affords every facility. With this two-thirds or the inch I
am enabled, by eye-piecing, to get nice definition up, say
to 200 or 250 diameters. Here we have a practical ad-
vantage arising from the use of a high -angled glass, and
one of the greatest value. In thus being able to dispense
with the use of covers a wonderful saving of time is
accomplished; the objective, too, is far enough out of
the way, so that it does iiot become clouded by the
evaporation, nor injured by the fumes of the re-agents.
Any desirable change in amplification that can ordina-
rily occur is furnished instantly by changing the eye-
piece. And here let me say that the oculars should slip
in and out of the tube just as easily as possible without
decentering the object viewed. A tight fitting eye-piece
is an abomination of the first order; any ocular of mine
will drop out of the tube instantly by tipping the stand
" upside down." Now the advantage of the short tube
is this : You are enabled to work over a table of the
ordinary height, and to view your object comfortably,
at the same time the table forms a very acceptable rest
for the forearm ; on the other hand, by keeping the tube
its standard length one must use a lower table, and the

CHOICE OF OBJECTIVES FOR REGULAR WORK. 205

rest for the arms can no longer be obtained unless some
recourse be had to blocking up by books and the like.

Now in an examination involving three or four hours'
time, it is quite possible that it may be desirable to sub-
stitute in the place of the two-thirds a glass that will
give higher amplifications. In this case the two-third
would be removed and the one-sixth called on to take its
place. Now I have previously found out that the one-
sixth has maximum performance when worked over the
thickest covers. These I have already selected and
placed in a little box by themselves, one of which is
carefully cleaned and placed over my object, the micro-
scope tube pulled out to the standard length, the instru-
ment inclined to a suitable angle, and thus the exam-
ination goes on. In extreme cases the one-tenth would
be again substituted for the one-sixth. With this glass,
having as it has, maximum performance at any point erf
its cover adjustment, there need be no particular care
exercised as to the selection of the cover, further than
to see that the same be thin enough.

It will be noticed that with the employment of the
immersions the tube should be restored to the standard
length. This is an important item, and should never be
omitted when there is nice work in hand. These wide-
apertured glasses are especially intended by the optician
to be worked with tubes of standard lengths. The
range of collar adjustment, too, is in many instances
arranged conformably thereto.

In observations over urinary deposits I contrive to do-
a great deal of work with the one-half inch. Of the

206 HOW TO SEE WITH THE MICROSCOPE.

two, the two-thirds or the wide-angled inch is much the
superior glass ; but I value these so highly that I dread
to use them over the fumes of chemicals. Hence I make
the cheaper glass do all that I possibly can, and in this
kind of a way the glass is really useful to me.

It will doubtless be observed that in changing from
the inch or two -thirds to the one-sixth or one-tenth I
make a pretty big jump. This has often occurred to
me, and has led to the trial of several intermediate
powers, resulting in every instance in my going back to
first principles; we are still of the notion that a No. 1,
four- tenths, or say three-tenths of the very highest
aperture possible, would be a valuable glass in the lab-
oratory, especially in such examinations as those of
urinary deposits or histological work generally, and we
hope before long to own just such a glass, which, if a
success, shall not be allowed to *k hide its light under a
bushel."

In the examination of malignant growths, and in the
study of minute pathology generally, the aforesaid pro-
gramme is somewhat modified. In this line one can
very often make entire and satisfactory examinations
with a " medium power " glass; therefore, and princi-
pally for the sake of convenience, I have in reserve a
dry one-fourth of 100°. This objective (the dry front
to my one-sixth) will give me nice, clean and reliable
views under ampliations, say from 200 to 600 or 700
diameters. • The mechanical working of its screw collar
is smooth and efficient, and the glass responds promptly
to any change thereof. Hence it has worked its way into

CHOICE OF OBJECTIVES FOR REGULAR WORK. 207

favor and use. It is not a strictly necessary objective in
the laboratory, for the one-sixth will of course do all
that can be expected of the one-fourth, and a great deal
more besides. The one-fourth is used precisely under
the circumstances stated ; when there is work on hand
likely to call for the shifting of objectives, the one-
fourth is very likely to remain in its box. Thus it will
be seen that my " working '' battery of objectives is not
numerically very formidable, and I may add, not very
•expensive.

Having thus stated my own course in the way of se-
lecting objectives for my particular work, let us now
turn our attention to a condition of things which is
occurring every day, to wit: A young physician just
graduated wishes to use the microscope in his (expected)
practice. It is important to him that the investment
in an outfit be made with reference to the strictest econ-
omy. The author has in the past, and is now, receiving
many letters of this sort, to one of which he replied
but a day or two ago substantially as follows :

The fundamental idea in purchasing an outfit ought
to be this: To buy nothing with the view of replacing
it bye-and-bye for something better of the sort, with an
indefinite hope that the original article can be disposed
of at no great loss. On the contrary, let every purchase
be made and every detail carefulty selected with the in-
tention of avoiding any future substitution or exchange.
Any departure from this fundamental law will be at the
sacrifice of strict economy ; therefore we reply to our
•correspondent in this tenor, recommending that he pur-

208 HOW TO SEE WITH THE MICROSCOPE.

chase a one-inch like those furnished by Mr. Gmidlach
or the Messrs. Beck ; and for a high power select the
professional one-fourth of the Messrs. Spencer & Sons,.
or its equivalent by any other maker. With these two*
glasses the physician can accomplish seven-tenths of any
and all work he may be professionally called on for.
Either one-inch named is a good reliable glass, giving,
when working with suitable oculars, very good shows
indeed, and infinitely better than the imported French
triplet, while the cost is but very slightly enhanced.
We recommend a one-fourth similar to the Spencer pro-
fessional, because, having used one ourselves, we can
speak " by the card." One very strong reason is, that
the adjusting collar mechanism (although moving the
front lens) is very smooth and satisfactory in its work-
ing. A still more important reason is that these glasses
respond nicely to any movement of the collar, and they
are, too, well corrected throughout the range of their
aperture. The purchaser is thus thrown early in con-
tact with an adjusting objective, and hence by his daily
practice will he become more and more skilled in its
use.

The author desires the reader to make a special point
of this: Many there be who, having bought adjustable-
objectives of poor quality, and having discovered "prac-
tically " that the position of the collar adjustment with
such glasses hardly affects in any way their efficiency of
performance, not only let them alone for the future, but
settle down strong in the faith that collar adjustment
don't amount to much, and that the " handling" of an

CHOICE OF OBJECTIVES FOR REGULAR WORK. 209

objective sometimes read about is simply a myth. Here
is another instance where the French proverb fits to a
charm. The fundamental error having been committed,
the evil consequences are sure to follow suit.

Now in the course of a year or two, our correspond-
ent having meanwhile obtained some considerable know-
ledge of the microscope, and being in a position to
make a further investment, he has simply to purchase a
first class inch (or two-thirds) of 45°, the old inch will
still do good service either as a "hack" lens for his
rough preliminary work, or it can be made to do yeo-
man's duty as a condenser, as has already been referred
to. It will, in very fact, be just as much needed as
before ; there will be no thought or occasion for its sale
or exchange.

It will probably happen, too, that in a little while
the one-fourth will be supplemented by the addition
of a one-sixth or one-tenth of high balsam angle. In
this case the great advantage derived from the previous
use of the one-fourth will at once be made manifest.
Our correspondent will be enabled to work the new
glass with tolerable satisfaction at sight, improving
daily as he continues its use; and if so be that he can
get a few words of instruction from some acknowledged
expert, they will be readily understood and appreciated.
And here, again, note that the one-fourth does not even
now become a superannuated, worn out objective, to be
sold at the first chance to the highest bidder. On the
other hand, it will continue to be used generally for a
considerable time while experience with the last pur-

210 HOW TO SEE WITH THE MICROSCOPE.

chase is being gained. In short, it will remain •' a
good thing to have in the house " until some genius like
Spencer or Tolles shall generally upset all our arrange-
ments by some master stroke of advancement. There
is no defence possible to provide against such an emer-
gency.

We desire here to say that our remarks as to object-
ives also apply as to the purchase of stands. The man
who purchases a stand "just for a year or two," as very
many have done, and are still doing, does so at a sacrifice
of true economy.

But we have correspondents of another class. Says
one, "the inch you name costs $7.00; the one-fourth
inch, $20.00, making $27.00; now I can't, for stand and
objectives, spend but $45.00, or at the very most, $50.00 ;
and then there is a sub-stage arrangement recommended ;
also, an extra eye-piece or two. What shall I do? This
is all the money I have got, and I have to take the
clothes off ni}T back to expend this much."

Now to all such, and there are many of them, we
reply, make a " virtue of necessity " The situation is
unfortunate, but, as you say, it cannot be helped. If,
by waiting a short time, things can be improved, then
you had better postpone your purchase. If to the con-
trary, then invest as best you may under the circum-
stances. Keep this in mind: Of the two evils, sacrifice
the stand rather than the objective ; the latter MUST be
maintained up to the standard given. You might pos-
sibly substitute, in place of the one-fourth, the best
three-tenths obtainable, non-adjustable; but there

CHOICE OF OBJECTIVES FOR REGULAR WORK. 211

would even then be but a few dollars " saved," with the
fact staring you in the face that you would lose all your
practice with an adjustable glass. This you must have,
and from the very start.

The author thus dwells on this matter because he feels
that it is one of deep interest to many. It is one, also,
that he has given particular attention to, that he might
be able to advise others intelligently; and he is not
without reason to hope that the information he has thus
tried to convey in the simplest possible language will
be to many worth more than the cost of his little book.
He is aware, that in writing the last page or two, he
has been practically repeating the tenor of what has
before been written; but nevertheless he is strong in
the faith that more than one of his readers will have no
fault to find with him on this score. To those about
purchasing an outfit of objectives he would further say
that the advice here given is precisely what he has given
to scores of enquirers during the past six years, every
one of whom have expressed their satisfaction in a man-
ner not to be mistaken. Let the reader, however, be
reminded that we live in an age of progress, and that
it is quite probable that the instructions offered here at
this date may at no distant day require essential modifi-
cations. Doubtless improvement will continue to follow
improvement in the future as well as in the past ; the
genius of our American opticians is such that anything
in the way of progress successfully accomplished seems
to render them more restless than before, and in view
of this, to use a nautical phrase, we advise the reader

212 HOW TO SEE WITH THE MICROSCOPE.

to keep well " an eye to windward." And it may be
here we can render quasi assistance, thus :

Judging the future from the past, it seems more than
likely that our opticians will at no distant day produce
one-fourth, one-fifth or one-sixth quite equal in every
respect to the one-tenth of to-day, and possibly with a
greater working distance. The author, within the last
twenty-four hours, has received reliable testimony af-
firming that young Spencer has succeeded in making a
wet and dry one-sixth fully up to the performance of
the one-tenth, of which mention has before been made
in these pages. This one-sixth we have not seen, but
are informed that it is now in the hands of an eminent
microscopist, who will exhibit it at the Paris expos-
ition.

Again it may be possible that the optician will suc-
ceed in enlarging the aperture of the low powers.
Heretofore 45° has been regarded as the limit of anofle

<> O

for the inch; with our present knowledge it appears
almost an impossibility to extend the present limit much
beyond the figure named, unless, indeed, the calibre of
the objective be increased. It will be advisable, never-
theless, to bear in mind that in the late march of ad-
vancement of the American objective, several desirable
points, formerly declared " impossible" have been mas-
tered by the optician, and are to-day " un fait accompli.'"
Now if it shall be so that the optician succeed in pro-
ducing a one-fourth equaling in angle and performance
the present work of the one-tenth, or that the one-inch
shall in the future rival the work of the two-thirds of

SELECTION OF COVERING GLASS. 213

to-day, then will the superiority of such glasses be
demonstrated, and for reasons already given, and we
are disposed to look in this direction for future improve-
ments. Let the reader also remember that the item
of " working distance" must not be lost sight of. For
. instance, if, in the extension of the one-fourth to the
capacity of the present one-tenth, the working distance
of the former should be decreased to that of the latter ;
then the real gain would be comparatively slight,
amounting practically to a saving of a few dollars in
the cost of the glass. The true problem is to gain
working force and efficiency without sacrifice of work-
ing distance. We recognize what has been accom-
plished, and the recognition is suggestive of further
advances in the same direction.

SELECTION OF COVERING GLASS.

This can be readily obtained of the dealers either in
sheets or ready cut into squares or circles, and of any
desirable thickness. As to the mere form of the cover
used, that is a matter of fancy; but the thickness ought
to correspond to the working of the objective. We
try to confine ourselves to three thicknesses of cover-
ing glass, namely, one-seventieth, one-one-hundred-and-
twentieth and one-two-hundredth of an inch. These
may respectively be denominated as thick, medium and
thin. It is a matter of the first importance that those
working first-class objectives should be well posted
as to the thickness of cover employed, and yet this tell-
ing point has been utterly lost sight of in the books.

214 HOW TO SEE WITH THE MICROSCOPE .

For example : By knowing the thickness of the cover,
one is enabled to approximately adjust the objective at
sight, and thus save time. We have thousands of
mounted objects in our cabinets, and .every cover has
been measured with all the accuracy obtainable. Those
who have long had their attention called to this item,
can, by dint of practice thus obtained, tell closely the
thickness of the cover by simply feeling it, and this, let
me assure the novice, is an accomplishment worth hav-
ing. Said the veteran microscopist of New York, Rev.
Dr. Armstrong, to the author, not long since, " It's
astonishing how fast you work. You seem to be in
perfect harmony with the objective." Now the secret
of the fast work noticed by the doctor lay in the fact
that I knew the thickness of all my covers, and was
thus enabled to place the collar of the object-glass very
closely in position at the very start; and not only this;
I was, for the same reason, posted as to the use of water
or glycerine. Now, to take a case from practice: Sup-
pose I desired to examine a brand new mount. Let it
be a difficult diatom this time. First, I run my finger
over the cover and instantly discover that it is a thin
one, say about like those used on the Moller plates.
Now, if I elect to use the one-sixth objective, I know that
this cover is too thin for Avater immersion ; hence glycer-
ine is chosen. I know, too, that over such a cover, and
with the glycerine intermedium, the objective will " cor-
rect" some three or four divisions from closed; there-
fore the collar is at once placed near such position.
Now, on looking through the tube at the object in posi-

SELECTION OF COVERING GLASS. 215

tion and focussed, suppose I do not get as good views
as I had reason to expect, then / let the collar stand as
it was and change the illumination until things are ap-
proximately as desired; this done, a slight turn of the
collar adjustment will insure the maximum working of
the objective. Now just contrast this with the usual
"modus." Ei^ht operators out of ten would have at
once twisted 'round the collar hap hazard like, by " rule
of thumb," probably wasting plenty of time, and, more
unfortunately still, condemning a really good objective,
and one that would have, with the proper manipulations,
given charming displays.

Now, in the instance quoted, we took the mount as
we found it, and "handled" it as best we could with
the least loss of time, the only means at our command
being the choice between glycerine and water as the
immersion medium. Now suppose the mount was one
prepared with especial reference to a one-twenty-fifth
or a one-fiftieth, and having an extremely thin cover,
say one-four-hundredth of an inch thick. Under these
circumstances it would have been imperative, to suit
the work of the one-sixth, that this thin cover be sup-
plemented with another and a thicker one, making opti-
cal contact with water or soft balsam. This is an in-
convenience which, in the case alluded to, cannot be
well avoided ; but we are nevertheless taught the pro-
priety of suitably covering such mounts as may be pre-
pared in "our usual line of practice. All this seems plain
enough, without further demonstration. Let the tyro
then cover his mounts as far as possible to suit the

216 HOW TO SEE WITH THE MICROSCOPE.

objectives under which he expects to show them, and
let him, too, early learn to discriminate as to the dif-
ferences in thickness of covering glass.

A handy instrument for measuring the thickness of
thin glass is a little pocket micrometer gauge manufac-
tured by the Brown & Sharp Company, of Providence,
R. I. Although not expressly made for the purpose, it is
as convenient and accurate as any other we have met,
while its cost is very moderate.* We make it a plan that
when a quantity of new covers are first in hand to pass
them over to the pupil, to be by him measured with the
instrument aforesaid, and assorted according to their
thickness, the various styles being kept in little boxes
by themselves, and duly labeled. In this way the stu-
dent acquires the needful practice, and the requirements
of the laboratory are met at the same time. If so be
that no instrument of the kind is at hand, or that the
observer feels that he cannot afford the necessary out-
lay, the usual fine adjustment of the stand can be made
to do tolerably effectual duty, thus : Obtain a cover, of
which the thickness is known, and with a fine pen dipped
in thick India ink, make a mark on one surface near the
centre; turn the cover over and make another similar
mark nearly, but not exactly opposite the first. Now
place the same under the microscope, focus on the mark
on the under side of the cover, and then, by the fine
wheel of the fine adjustment, focus again on the mark
on the upper surface, noting the revolutions or parts

* As we have before remarked, the fine adjustment of the Acme can be
used as a micrometer.

BECK'S VERTICAL ILLUMINATOR.

217

thereof traversed by the wheel. By this simple proced-
ure a gauge is established from which other covers can
be easily measured. Some stands have the wheel of the
fine adjustment graduated, which will be found especially
convenient. In other cases the observer can make his
own graduations on a little circle of paper and adapt
the same to the wheel, without any great drain on his
mechanical skill.

BECK S VERTICAL ILLUMINATOR.

This instrument consists of a brass tube, either end
being fitted with the " society screw," so that it can be
attached to the back of the objective; the object-glass
with the iluminator thus attached is screwed to the nose
piece of the stand. The tube has an adapter of its own,
so that it can be revolved around the optical axis of the

218 HOW TO SEE WITH THE MICKOSCOPE.

microscope. In this tube is placed ti circular glass disk
(one of the ordinary circular covers used in mounting-
object slides). This disk is supported in position by a
horizontal pin, to which it is iastened with a bit ot ce-
ment, the pin passing to the outside, and terminating
with a little knob, by which the disk can be revolved
at will. The tube is pierced laterally with an aperture
for the admission of light. The light from an ordinary
hand lamp passing through the aperture is received by
the little glass disk, and, by turning the outside knob
properly, is made to pass vertically downwards to the
rear of the objective, and by it in turn concentrated on
the object to be examined ; no sub-stage or other illu-
mination being used. This is the instrument as made by
the Messrs. Beck, and is in fact but a modification of &
similar instrument invented by Prof. H. L. Smith, of
Geneva, N. Y. Prof. Smith's device, however, is fur-
nished with an interior metal reflector in place of the
glass disk of the instruments of the Messrs. Beck.

We had used the illuminator but a very short time
when we discovered that the definition of the objective
was very much improved by shutting off the area of the
lateral aperture, thus allowing less light to enter. We
also found that the actual amount of light needed de-
pended on the objective employed. In most instances
the higher the angle of the object-glass, the smaller
should be the area of the lateral aperture.

About the time we had arrived at the above fact, the
Hon. P. H. Watson happened to call in to spend an
hour or two " over the tube." The conversation turn-

BECK'S VERTICAL ILLUMINATOR. 219>

ing on the action of the Beck illuminator, we coupled the-
instrument to my Tolles one-tenth and worked them
over Mr. Watson's Nobert test-plate, and in a very short
time succeeded in getting a most charming display of
the 19th band, and while the latter aperture was nearly
closed by interposing the circular edge of a large bull's
eye condenser which happened to be at hand on the
table.- Mr. Watson and myself were both delighted
with the exquisitely beautiful display of this so-called
difficult object — this 19th band. Other severe tests
were also taken in hand and resolved. Among others
we had a glorious show of podura under amplifica-
tion of some 4,000 diameters. It was demonstrated,
too, that the very best resolutions were only obtained
when more or less of the lateral aperture was closed by
interposing the circular rim ot the condenser, the clear
aperture left being in the form of a crescent. Subse-
quently Mr. Watson devised the following described
attachment, which answers the purpose fully :

The lateral aperture of the instrument is somewhat
enlarged and a hollow plug inserted therein, the opening
in this plug being the same calibre as the original aper-
ture. The plug is somewhat tapering, and fits the open-
ing "spring tight." It also projects outward slightly
beyond the circumference of the main tube. To the outer
end of the plug is fitted a little shutter, while a narrow
slit, about oiie-one-hundred-and-fiftieth of an inch wider
is pierced through the shutter ; the whole so arranged
that the opening the plug can be partly or wholly closed 9
or the little slit used by itself; and when low powers are

220 HOW TO SEE WITH THE MICROSCOPE.

employed, or objectives of narrow apertures used, the
entire attachment can be removed if desired. This
illuminator, as originally designed, was intended for
use with dry objectives and with moderate magnifica-
tions ; the idea of using it with immersion glasses of
high angles and under high powers, originated with
George W. Morehouse, Esq., of Way land, New York,
who is well known as an expert and accomplished mi-
croscopist. The special advantages obtained by the
immersion system in the case in hand are too apparent
to need further mention. It will be noticed, too, that
the Beck is thus made to do duty — like the Wenham
reflex — in a way quite foreign to the purpose of its
original inventor.

The advantages derived by the use of the instrument
are : First, we are thus enabled to view objects by the
aid of reflected light; the so-called " opaque illumina-
tion," under the highest amplifications and (if the proper
objective be employed) with superb definition, as is
attested by its unequaled work over the Nobert 19th
band ; and by the employment of artificial light, a com-
mon kerosene hand-lamp being all that is required. In
this respect the instrument stands alone and inimitable.
Second, the views given are surface markings only.
There is no "penetration" here. The focus must be
most accurately drawn, and on the surface of the object.
The slightest deviation therefrom is instant and total
defeat. Thus we are enabled to locate structure, at
times a most valuable assistance to the observer. Third,
by a slight change in the position of the lamp, the mir-

BECK'S VERTICAL ILLUMINATOR. 221

ror being at the same time brought into play, the illu-
mination may be almost instantly changed to that
of transmitted light, or from thence back to reflected
light again. This cross-questioning under two methods
of illumination is often of great advantage.

Per contra : The vertical illuminator has but one
drawback, and that is rather a serious one, to wit: Ob-
jects to be displayed under it must be mounted dry, and
also contact the cover. Hence it will be seen that a
large portion of histological, pathological, as well as
other permanent mountings, are excluded from use.
Many of these can be temporarily prepared for study,
and it is hoped that the attention of observers will be
enlisted in this direction. Admitting the serious char-
acter ot the objection named, let us bear in mind that
there remain countless fields of research wherein the
"Beck" will certainly prove an instrument of the
greatest value.

The tyro will find the Beck illuminator a difficult in-
strument to use, and his first attempts will probably
result in failure. Nor is it an easy task to give any
instruction in writing that will be of much aid. The
instrument not being a costly one, and likely to be gen-
erally used when it shall become better known, we will
try and furnish a few hints that perchance may prove
of value to the beginner.

The novice will do well, at his first attempts, to select
a dry mount, one that he is perfectly familiar with, and
preferably scales from the lepidoptera ; a dry mount of
podura will answer very well, indeed. Select, also, the

222 HOW TO SEE WITH THE MICROSCOPE.

highest angled objective, and with this examine the
mount in the ordinary way and get a tolerable correc-
tion for the glass. Next, removing the object-glass
from the stand, couple it to the illuminator and screw
the whole to the nose-piece of the stand, using trans-
mitted light, as usual. Focus the objective. Now hunt
through the slide ; among the numerous scales will
probably be found one or two which, in order t^ bring
in focus, the objective will require to be withdrawn from
the cover slightly. In such a case the chances are that
that particular scale is nearer the cover, and if in good
condition may be selected for further operations. Next,
bring the lamp (a flat wicked one) towards the observer,
revolving the tube of the illuminator so that the lateral
.aperture shall be in proper position to receive the light
from the lamp, the latter being about seven or eight
inches distant, and the flame about the same height as
the aperture of the illuminator. Now grasp the little
knob connected with the interior glass disk and turn it
.so that light shall be reflected to the rear of the object-
ive; at the same time, and looking through the tube as
you catch the first glimpse of light, revolve simultane-
ously the main tube and also the little knob carrying
the glass disk, the object being to secure as great an
amount of light as possible. A little manipulation of
this kind ought to result in illuminating the object with
a horizontal (or nearly so) band of light. The next
step will be by a slight movement of the lamp, keeping
Its edge exactly towards the aperture, to endeavor to
make the band of light crossing the field as narrow as

WORKING WITH LOW POWERS. 223

possible, and the outlines of the band clear and distinct.
By this time the operator will have probably discovered
that a slight rotation of the main tube will separate
the horizontal band into two parts, or, as some of my
pupils express it, " two tongues." The best position is
when these are made to coalesce as completely as possible.
It is also probable that in the attempts thus far made
that the imao-e of the scale has been well seen. When
this occurs it should be at once focussed. The next
procedure is to correct the objective; the correction
obtained by transmitted light will not suffice for the
purpose in hand. It will be noticed that as the glass is
made to approach the correct adjustment, the horizontal
band of light will be correspondingly improved. So
true is this, that one might almost be governed thereby
in the adjustment of the objective. Having got thus
iar along, and without any serious mishap, it will be
easy, by closing the shutter, to admit the precise and
most favorable amount of light, and also to try the
effect of sundry very slight changes in the position of
the main tube, glass disk and lamp. Very beautiful
resolutions are sometimes obtained by bringing the lamp
within five or six inches and interposing the bull's eye
condenser, flat side to the lamp, in which case the shut-
ter must be further closed. It will happen also, occa-
sionally, that the best exhibition of striae on very diffi-
cult objects, §uch as extremely close fiiistulia saxonicas,
is when the striae are placed at right angles to% the hori-
zontal band of light.

Now, should the manipulator meet with tolerable sue-

224 HOW TO SEE WITH THE MICROSCOPE.

cess, and get good shows of the lepidoptera, I recom-
mend that he practice for some half-dozen sittings over
the same mount. By this he will get a certain familiarity
with the instrument which will be of great value to him.
The chances are, too, that he will wonderfully improve
in the manipulations, and in this alone will be well
enough rewarded for his pains. Furthermore, he will
learn what nice effects can be had by the slightest changes-
in the position of the tube, glass disk, shutter or lamp,
and the necessity for the closest focussing will be taught
practically.

Having thus got tolerably acquainted with the instru-
ment, let the operator try changing from reflected to
transmitted light, and vice versa, which is accomplished
merely by moving the lamp back to its first position,
employing the mirror just as was recommended at the
start. A little practice of this nature, working alter-
nately by transmitted and reflected light, will soon
accustom the observer to the situation, and enable him
to make the change in illumination almost instantly.

A fact worth knowing is this : The combined length of
the illuminator and objective will, if the objective selected
be one of the extremely long models, defeat its use 011
some of the smaller stands. Thus we find that we can-
not use the illuminator with a Tolles one-sixth or one-
tenth on the little " Histological" of Mr. Zentmayer,
there not being sufficient room between the "jacket'*
in which the body tube slides and the stage to receive the
illuminator and objective when coupled together. We

BULL'S EYE CONDENSER. — LOW POWERS. 225

are therefore, when essaying the use of the Beck, com-
pelled to fall back on a larger and heavier stand.*

BULL'S EYE CONDENSER.

This instrument, so well known, and accompanying
almost every stand as sold, we make nearly constant use
of. It should be simply a large plano-convex lens, say
from two to three inches in diameter, and fitted with
universal mountings. It has been too general a rule with
the microscope makers to "adapt" the size of the con-
denser to that of the stand. Thus, if a certain maker
furnish -five or six different sizes of stands, he will be
pretty sure to have as many sizes of condensers to accom-
pany the same. But let the reader insist that, however
small may be the model of the stand selected, the con-
denser be at least two inches in diameter, and that even
three inches will be found none too large. Any of our
opticians can furnish the instrument made to order.
We have seen and worked with several made by Zent-
mayer to accompany his large and intermediate stands,
and also the large model furnished with the Messrs.
Beck, all of which were effective instruments. •

WORKING WITH LOW POWERS.

It has been our primary intention throughout this
work to avoid repetition of instructions, hints or sug-
gestions, such as may be found in the various text-
books, while interspersed among the pages already writ-

* The construction of the " Acme " admits the use of the Beck illumina-
tor.

15 Microscopy.

226 HOW TO SEE WITH THE MICROSCOPE.

ten the reader may perhaps recognize information as to
every day work which, perchance, he may turn to some
account. There remains therefore but little for us to
•add under the above caption. Without hesitating to
repeat in a more condensed form the same ideas which
liave heretofore been scattered through our pages, we
proceed to give other methods of working with the
lower powers.

First, we use and recommend a stand fitted with a
swinging sub-stage, preference being given to the one
that will allow the mirror to rise above the level of the
stage. Stands there are which although allowing a lim-
ited swing, do not afford the extreme range of motion,
while scores there be fitted with stationary sub-stages
and fittings. Of the last two named, that with the lim-
ited range is infinitely to be preferred. One of the prin-
cipal advantages arising from swinging the mirror above
the stage is that we are enabled thus to condense either
sun or artificial light on the top of the object, and it is
possible to accomplish this otherwise than by the swing,
by simply attaching a mirror to a separate adjustable
stand of its own. In whatever arrangement which may
be selected, let it be imperative that the mirror be attached
directly to the swinging arm, and at the proper focal
distance, and that the centre of rotation coincide with
the plane of the object on the stage. Any adjustable
and intermediate joints between the mirror and the
swinging arm, allowing the foroier to be placed out of
its focal position, is, in the opinion of the author, an
intolerable nuisance, and one not to be submitted to un-

WORKING WITH LOW POWERS. 227

der any conditions short of sheer necessity. Now of the
two styles of stands, the one with the full swing and
the other with the partial swing only, premising that
both mirrors rotate in the plane of the object, there
will not be a great deal of choice for general work.
Nevertheless it costs no more to manufacture th'e one
than the other, and hence the perfect stand becomes no
more costly than one that is to a certain extent imper-
fect. Therefore we urge, why not procure the best,
provided there are not especial and governing conditions
patent to the purchaser. The substance of all this has
been placed before the reader, and in again calling his
attention, it is hoped that the repetition will gather
force.

Now all the information we have to offer as to working
with the low powers will refer entirely to the use of the
low-angled sub-stage condenser conjointly with such a
stand as we have recommended. As has been before
remarked, the introduction of the swing has worked a
radical change in our ideas as to the value of the con-
denser, and the instrument is now with us a constant
fixture, and in daily use.

With the use of the condenser we have at command a
greater amount of light, but this is not the special advan-
tage derived from its use ; and then again it is easy to make
the bull's eye do duty in its place. Of the two accessories,
the bull's eye is the more simple and convenient- to use;
nor will objects occupying the entire or greater portion
of the field when illuminated with the condenser appear
more brilliant and enticing than without it. The grand

228 HOW TO SEE WITH THE MICROSCOPE.

advantage obtainable with the condenser is, that by a
careful manipulation of the apex of the small cone of
light we are often able to get just the right illumination
on certain details of our object, while the field generally
is kept in partial light only, " toned down " as it were.
This effect may be produced in two ways: First, by
raising or lowering the condenser; and, secondly, by
swinging the sub-stage laterally to a point but just-
within the aperture of the objective employed. We
sometimes use the one plan and sometimes the other;
and then, again, we often use a mixture of both, and,
as a rule, the better illumination will be attained when
the condenser is somewhat within, or without the focal
point.

Now let the novice understand that in thus employ-
ing the condenser there is no attempt to get " pretty dis-
plays " of the object. On the other hand, the primary
object is to obtain cool and reliable definition of struct-
ture. Those who thus use it will, I think, be pleased
with the results attained. It is somewhat more " bother "
than taking the light- directly from the mirror, or with
the usual intervention of the diaphragm. Notwith-
standing this, one soon becomes accustomed and addicted
to its use. The swinging stage, too, is a valuable ad-
junct to the old diaphragm, and with this latter instru-
ment superior effects can be had working on the same
general plan as with the condenser, and using a small
aperture to the diaphragm. Should the light be too
weak it can be assisted by interposing the bull's eye, or
light can be shut off by depressing the diaphragm.

WORKING WITH LOW POWERS. 229

For ordinary work by daylight we use the plain mir-
ror in conjunction with the condenser; and let me here
again insist that the latter be such as has already been
described, i. e., of low aperture, admitting but a narrow
cone of light. In very dark days the light can be rein-
forced by employing the concave mirror, a plan not gen-
erally recommended, but nevertheless quite practicable.

For reasons before given, we greatly prefer, for regu-
lar right straight along daily work, to use the stand
with the tube short, keeping, for the most part, the
tube vertical, dispensing, too, with the stage clips, and
simply laying the preliminary mount thereon, shoving
it about in every direction required, by the fingers.
Those who have been accustomed to confine the slide
under the clips, as is generally done, will not, on the
first trial, be likely to endorse my practice. Let me,
then, to all such, especially recommend it. By thus
allowing the slide to rest by its own gravity alone, one
soon acquires a delicacy of finger manipulation that is
of very general value; while, per contra, the clips are a
real hindrance to fast work. Those who have the pa-
tience to practice without them for one solitary week
will not be likely to get back into the old rut.

The height of the work table should vary with that
of the observer ; such a table as one would naturally
elect to write on will be about the correct height for
microscope work. This, if the low angled condenser is
to be generally employed, may be placed at a consid-
erable distance from the window, but care should be
taken that the light conies from the left. If there be

230 HOW TO SEE WITH THE MICROSCOPE.

other glazed openings in the room liable to form cross-
lights, they should be closed by shutter or curtain.
The table selected should be solid and heavy. Any and
all of the little light affairs in cherry and mahogany
offered at the furniture stores are totally unfit for a mi-
croscope table; but the crowning nuisance of the lot is
the revolving table, made expressly for the microscopist,
and sold at outrageous prices. Castors, also, are to be
rejected. In short, anything that detracts from the sol-
idity or rigidity of the work-table is to be eschewed.
What the observer wants is a firm support for his stand,
free from shake or tremble — one that he can lean against
freely when weary, and one that he may even run against
accidentally without inaugurating any serious calamity.
A couple of drawers placed in the front are a convenience
for storage of accessories, etc., and these, being partly
opened, form convenient rest at times for the forearm.
The table should be sufficiently large and roomy. Three
by four feet is none too large.

THE SPENCER ONE-INCH OF 50° — BROAD-GUAGE OBJECT-
IVES, ETC.

In the spring of 1878 we received from the Messrs.
Spencers an inch objective of 50° aperture. This glass
was made expressly to our own order.

Our purpose in ordering the above glass was to deter-
mine whether it was possible for the Messrs. Spencers
to furnish an inch objective having angle and definition
equal to their celebrated two-thirds.

With the new inch our experience has thus far been

BROAP-GUAGE OBJECTIVES, ETC. 231

necessarily limited; we have, however, instituted a few
comparative tests which we now present to our readers.

The working distance of the two-thirds worked with
one- fourth inch solid ocular and standard ten-inch tubes
istwenty-five-one-hundredths of an inch.

The working distance of the new inch with same oc-
ular, worked with ten-inch tube, is thirteen-one-hun-
dredths of an inch ; when worked with the same eye-piece
and the short tube of the " Histological," the working
distance is increased to eighteen-one-hundredths of an
inch.

In general, the definition of the inch is superior to
that of the two-thirds. The very best definition of the
latter is obtained by the use of the full length tube and
one-fourth inch ocular, while the highest definition of
the inch is reached by the use of the short tube and
same ocular.

The inch, worked over the balsam ed Moller plate, gives
readily nice shows of the transverse striae of P. Balti-
cum, and with a little management both ssts of lines
are brought out. On the G. Marina, immediately pre-
ceding the Balticum, and really the more difficult shell,
the inch gave me a very nice stand of the transverse
striae from end to end of the shell, its performance over
this diatom being manifestly superior to that of the
two-thirds.

On dry mounted shells of the P. Balticum the two
sets of lines are very well displayed by the inch, as are
also the transverse striae of dry angulatum, a favorable
frustule beiii£ selected.

232 HOW TO SEE WITH THE MICROSCOPE.

Over the Kobert test plate the inch gave me the 9th
band, = 56 X lines in .001, Eng. inch.

Working the two-thirds with the one-half inch ocular
and full length tube, and the inch with one-fourth inch
ocular and short tube, the amplifications were about
equal ; the inch in every instance affording the better
definition.

According, then, to the inch manifest superiority in
point of defining power, its shorter working distance,
which in its most favorable aspect is 33 per cent, less
than that of the two-thirds, must receive due consider-
ation, this decrease, too, of working distance will be
accompanied by some loss of "penetrating power."

A mueh mort important point, however, to the author
was to ascertain if the focal distance of the inch was
sufficient to allow its being worked over wet and uncov-
ered mounts without clouding from the evaporation.
To test this, we used the glass an entire evening in reg-
ular routine work over urinary deposits, and without
experiencing the least trouble from the source named ;
while on the other hand the general behavoir of the
objective while thus engaged in practical work was most
satisfactory.

The reader is reminded that in comparing working
distances of long focus glasses, the same percentage of
weight does not obtain as would occur in comparisons
of object-glasses of nominally short focal lengths, and
giving high amplifications.

A word or two concerning the standard " society

BROAD-GUAGE OBJECTIVES, ETC. 233

After experimenting with the wide-angled inch, as
above related, we wrote to the Messrs. Spencers, asking
them if it was possible either to still further extend the
angle of the inch, or, maintaining the same aperture,
to increase its working distance. In reply, the elder
Spencer informed me that it would be difficult to fur-
ther increase the aperture or the working distance unless
the diameter ot the objective should also be enlarged.

From this it would seem desirable to increase the di-
ameter of our low-power object-glasses, and this in turn
necessitates a change in the construction of the micro-
scope stand. Mr. Bullock's large stand, as also the Acme,
are especially arranged to accommodate these " broad-
gauge" low-power objectives.

An one inch objective of large calibre is now in pro-
cess of construction for the author. The optician hopes
to endow it with an aperture of at least 62°, maintain-
ing a working distance of one-eighth of an inch.

It is but a simple act of justice to say that the idea
conveyed to me by Mr. Spencer had already occurred to
Dr. W. W. Butterfield, of Indianapolis, Ind. While
in attendance at the congress of microscopists held in
Indianapolis in 1878, Dr. Butterfield showed me a
broad-gauge four-inch made to his order by London
opticians. He had also a stand then in process of con-
struction, and designed for the use of this class of ob-
ject-glasses. This, however, at the date mentioned, had
not arrived; consequently there were no accommoda-
tions for an examination of the objective. Should my
own glass be completed before these sheets go to press,

234 HOW TO SEE WITH THE MICROSCOPE.

some account of its performance may herein be expected.
Meanwhile, there seems to bo no good reason why, with
the increase of calibre of our low-power objectives, there
should not also obtain those advantages due to aperture
•»nd working distance.

CHAPTER VII.

WORK WITH THE HIGHER " POWERS."

For this class of work we have in the preceding pages
unhesitatingly expressed our preference in favor of ob-
jectives of the widest aperture. Such are the instru-
ments we ourselves use daily, and can confidently recom-
mend to all who may be desirous of working with the
best instrumentation obtainable. Therefore, whatever
we may have to offer in the way of instructions sug-
gested by the above heading will be solely applicable
to the class of objectives generally known as " wide-
angled," to which we have given in the past, and pro-
pose yet to give in the future, a large amount of careful
study and attention. And first of all it becomes neces-
sary to disabuse the mind of the student of some of the
popular fallacies which have found outlet and circulation '
through the medium of the microscopical periodical
literature of the present and past few years. These, as
will be discovered by the attentive observer, are par-
oxysmal in their nature ; in fact are veritable " chateaux
en espagne," at once inconsistent in detail, and roundly
absurd when contemplated as an entirety. Thus it oc-
curs that at one moment the student is taught that wide-
angled glasses are extremely inconvenient; that great
attention has to be bestowed on the adjustment and illu-
mination, etc. ; while on the other hand, another " au-

235

236 HOW TO SEE WITH THE MICROSCOPE.

thority" subsequently insists that the so-called "hand-
ling" (?) supposed to be necessary to the use of the
wide apertures is simply a myth — a downright farce ;
and that any one possessing a fair quota of intelligence
can easily acquire all that is to be acquired in the work-
ing of an adjustnlAe glass. Nor need one hunt long or
dig very deep to find other " authorities" teaching that
all this handling" " although essential to the optician"
is no manner of use to the practical observer, unless he
has so far degenerated as to aspire to the distinction of
being simply a " handler " and a u fighter."

Let the author, then, and in view of the situation as
presented, inform those proposing to study the microscope
with the intention of becoming in due time accomplished
observers, that there is no " royal road " to success ; that
to become even so sufficiently expert as to enable one
to follow out (leaving original work out of considera-
tion) the investigations already made and published by
eminent microscopists, will require quite as much effort
and study as would be called for in graduating from any
college in the United States. The curriculum is a broad
one in its very nature, involving a thorough knowledge
of instrumentation, and when by means thereof we are
enabled to see well, it then becomes a positive necessity
to judge well of what is seen, and this in turn can only
be well accomplished by those having eyes well trained
to the work in hand. There is, moreover, work for the
brain outside of the functions of the optic nerve.

In the micrographic dictionary, by Messrs. Griffith &
Henfrey, I find, (page 11,) the following: " Above all.

WORK WITH THE HIGHER " POWERS." 237

however, it must never be forgotten that microscopic
investigations require more time and patience than per-
haps any others, even in regard to the determination of
simple facts of structure and qualitative composition \
and although it is not very uncommon to hear those en-
gaged in them sneered at as wasting their time over a
very simple plaything, this may be regarded as arising
from one of those prejudices which will exist so long as
people will venture to express opinions upon matters with
which they are unacquainted, and which are beyond their
comprehension."

The above quotation is well worth reprinting on its
intrinsic merits, and it may be that we shall find some
especial use for it bye-and-bye. Meanwhile, this mat-
ter of eye training calls for a word or two, for, among
the accomplishments tha,t go to make the first class ob-
server, this education of the eye is generally supposed
to be quite as much a myth as the capacity to " handle "
an object glass. Let us take an item or two from our
personal experience :

Not long since the author had the honor to address a
select party of gentlemen at the parlors of a private-
residence. In the course of his remarks the matter of
u eye-training " was brought prominently forward and
its usefulness urgently insisted on. Subsequent to the
close thereof a gentlemen present stepped up to him,
saying, " I want a little talk with you about that eye
business, which you seem to regard as a sine qua non.
I do not see that thing as you do. You and I are about
the same age. We have both of us necessarily been

238 HOW TO SEE WITH THE MICROSCOPE.

using our eyes constantly all our days. If I look across
the street and see a house, why, so can you; and thus
we have been respectively seeing houses as well as other
things all through life. In short, our eyes have been
constantly at work, and have thus been as constantly
trained. It may be that you have abused yours by over
work with the microscope — if that be the case, I reckon
mine have the best of it. At all events, I can't see
how you can establish any individual superiority as to
vision."

At this moment Prof. Huber had seated himself at the
piano and was entertaining the company by his superb
renderings from classical authors. In reply, I said:
what you affirm as to the eye must be similarly true of
the hands. Prof. Huber and yourself are apparently of
the same age, and both of you have been using your
hands " all your days." Whence comes that lightning
rapidity of action; that wondrous delicacy of touch?
Think you that the professor has abused his muscles by
•over work with his five finger exercises, or that you
have any claim to digital superiority? But to confine
the case strictly to the eye alone ; IIOAV comes it that the
mariner can, not only detect a " sail " near the distant
horizon, but can also state with accuracy whether it be
.a ship, brig, or schooner, and the direction the " sail"
may be pursuing, to all of which the passengers present
will be totally blind?

Noi need we " go to sea" to find instances illustrative
of the issue in hand. The eye of the artist recognizes,
perforce of his experience with the esthetics ot nature,

WORK WITH THE HIGHER "POWERS." 239

beauties, to which that of the shepherd boy is innocently
•enough a stranger, and of the two, permit me to inquire
which would make the better rnicroscopist?

As far as our auditor is concerned, we rest the issue
on its merits.

A few years ago we purchased for a gentleman well
known in microscope circles, a wide apertured objective.
The party was no novice, but on the contrary a real
hard and close worker with the instrument; and fur-
thermore, the gentleman had formerly filled the chair
of microscopy in one of our most honored colleges.
After working with this glass for about one year, he
applied to me for instruction in the use of this instru-
ment, proposing to spend his vacation with me, and for
this purpose the author was delighted with the proposal
and the arrangement was consummated by unanimous
consent. Now the main point actuating my honored
pupil was this : He had used his glass considerably—
-enough to discover that there were conditions involved
that he could not control as he desired. Sometimes he
•could see better than at others; sometimes the glass
would work good naturedly, and then again, at others,
it wouldn't work well. In the course of instruction
which followed, a slide of navicula rhomboides was se-
lected (this, by the way, was a diatom) and placed on
the stand for examination with the objective named.
In point of tf difficulty" these shells would have been
regarded as average specimens. We then took some
little time to explain as well as we could the behavior
of the object glass when in and out of adjustment, as

240 HOW TO SEE WITH THE MICROSCOPE.

exhibited by the object selected. Our reason for mak-
ing at this time the particular selection was this : When
the objective was in perfect adjustment, the striae were
admirably well seen when the inch ocular was employed,
but were assumed to be invisible under the two inch.
Next, the pupil was required to adjust the object glass
using the two-inch ocular only, acting, of course, under
the general instructions he had received. This done he
was to apply the higher eye-piece and learn of his suc-
cess, practically. Our friend went at his task manfully,
and fought that slide of diatoms three hours or more
daily for more than a full week, constantly improving
in its manipulations. Then it occurred that, getting
somewhat weary of his protracted efforts over one and
the same slide, he began to beg for a change to do some-
thing else. Nevertheless, he was put off time alter
time, until nearly at the close of a long evening's work
he jumped up from his table, and running towards me,
his eyes beaming with joy, exclaimed, " I have it! I
see it! It's all plain sailing now!" "Well," said IT
"what is it?" He replied, " I can see any shell on that
slide, I care not how srnall nor how close the stride, and
as well with the two-inch ocular as with any other; and
more than that, I can put the correction collar right on
the clot without humming or hawing, and do it every
time." To this we responded: " You have now solved
your problem, and are ready to tackle another mount
at our next sitting.

Now, reader, here is a practical case in point: My
pupil had not only been improving himself in the "hand-

WORK WITH THE HIGHER " POWERS." 241

ling " of the object glass, but all this time his eye was
becoming educated. At the commencement it would
have been an utter impossibility for him to have recog-
nized the striae of the rhomboides with but the two-
inch eye-piece, nevertheless the writer saw them splen-
didly, and with that exquisite definition which per-
tains only to the work of these high-angled glasses.
Had 1 told my pupil this at the start, he would proba-
bly have received the assertion in a becoming manner,
meanwhile entertaining some " first class doubts " under
his sleeve;" full fledged doubts, too, and simply wait-
ing for a fine day to fly.

Place the microscope in the hands of the shepherd
boy ; its total defeat is established. Adjust, if you will,
the objective with the utmost nicety, and arrange the
illumination to perfection, and total defeat still reigns
tiiumphant. He neither has the capacity of seeing well
nor of judging well of what may be seen, neverthe-
less, he can honestly and innocently look you squarely
in the face and assert that he has as good a pair of eyes
u as the next man."

We have thus taken some little pains, and hope not
without profit to the reader, to establish a fact well
kmvn to all who are expert in the use of the microscope.
If our views are correct, it obtains that no inconsider-
able amount of time and patient care and study are each
individual elements in the outlay necessary in the effort
to become an accomplished observer, and if this is to be
considered in the light of an evil, then let it be remem-
bered that "there are no evils unless attended with

Microscopy 16

242 HOW TO SEE WITH THE MICROSCOPE.

some corresponding good." And fortunate it is, in the
case before us, there is a fascination accompanying the
intelligent use of the microscope knowing neither limit
nor bounds, and the task of becoming well acquainted
with the use of the instrument is merely a labor of love.
There is another aspect of the matter which deserves a
word or two, to wit: The popular idea with many is,
that if there be a certain amount of eye training essen-
tial in the use of the " high powers," this has no appli-
cation to those who use the lower amplifications. Says
one, " you are all right about your eye education when
there is such nice work as showing1 the 19th band in

O

hand; but then you see most of my work is done with
the inch, and that's quite another thing." Now there
is just as much error here, but it is of a less serious
character. The truth is, the expert can see more with
the inch, and by the "expert" I mean (for the time
being) those referred to who are able to display hand-
somely such tests as the 19th band. Every day expe-
rience with pupils in the laboratory demonstrate this
fact pointedly. Thus; At the commencement of his
practice, the novice is quite content with the meanest
French triplet the premises afford, but in less than a
month he will hold it in perfect contempt, and his sub-
sequent progress will to a great extent be properly
measured or indexed by the constantly increasing capa-
city to handle even these non-adjusting glasses.

In thus insisting on the necessity of the proper- edu-
cation of the eye, let us look for a moment to its im-
portant bearing on a particular class of observations.

WORK WITH THE HIGHER " POWERS." 243

We intended to refer to this bye-and-bye, but it finds
an appropriate place rig-lit here. We may, however,
refer to it at some future time. I allude to that class
of work intimately connected with the use of object
glasses of wide apertures, and over exceedingly difficult
lined structures; for instance, the display of the striae
of amphipleura pellucida. But let the reader remember
that this class of work is not confined to the study of
diatoms.

To illustrate what we have in hand, reference is made
to the following sketch : Let C-D and G-H be a sec-
tional view of some " difficult " diatom, such as amphr
pleura pellucida or the like, the short lines 1, 2, 3, 4?
etc., representing in section the elevations of the striae;
M and N being views " in plan" as seen conditionally
in the microscope. Let us first consider the effect of
illuminating C-D with direct central light, as indicated
by the line A-B. The effect will be as shown in plan
at N, to wit : There will appear but a series of exceed-
ingly fine lines; so fine (mark the words, not necessa-
rily close) that it will be impossible to see them with
any glass extant. Recourse must then be had to " ob-
lique illumination." Now let C-D, as duplicated at
G-H, be illuminated by the oblique beam E-F. The
effect of this is shown in section at 1', 2', 3', etc., and
in plan at K, where we have the view as displayed in
the microscope. Here we have two things successfully
accomplished; the striae which in the former case were
so " fine " as to be invisible have now become broad and
can easily be distinguished by the eye; and, secondly,

244

WORK WITH THE HIGHER "POWERS." 245

this last display is as false, as to many it has been ac-
ceptable. Now let down the obliquity of the illumina-
tion, as indicated by the line I-J; the effect is noted on
the sketch at L, and with a first class high balsam angled
objective and an eye well trained, it may be that the
striae are not only discernable in the microscope, but the
observer will further be able to note the intervening
spaces also ; and this, too, which the certain knowledge
that of the varying condition set forth, the latter dis-
play is not only the most satisfactory in general terms,
but the most truthful. It is also apparent that the
more we decrease the angle of the illuminating beam
the louder the call on the defining power of the object
o*lass and the greater the demand for education on the

o °

part of the eye. In other words, the expert, all other
things being equal, with a pair of eyes trained by long
practice in his profession, has the better chance of see-
ing things as they actually are. From the illustration
given we deduce several propositions, viz:

First, it is always better to see structure somehow
than not at all. Let those addicted solely to the use
of narrow apertures ponder this well.

Secondly, when engaged in investigations of " diffi-
cult" structure similar to the case presented, and calling,
at the best for light of considerable obliquity, the less
of the obliquity, as a rule, and within certain limits, the
better ; and the more perfect the education of the eye
the less will be the call above mentioned.

Third, the higher the balsam angle of the glass the
LESS will be the obliquity required. Let those who

246 HOW TO SEE WITH THE MICROSCOPE.

favor work with centrally disposed light make a note
ol this.

Says one (alluding to the second proposition), I don't
exactly see that thing as you do. Suppose, for instance,
that the objective and the eye were both so perfect as
to allow the illumination to become axial, as in your
first illustration, wouldn't that be better still?

We reply, ask the artist if he would prefer the land-
scape thus lighted. The architect of the universe ex-
pressly arranged things to prevent such a catastrophe.
A certain amount of shade is as necessary as that of
light. Such a thing as " dead central illumination,"
although often talked about, is a myth.

Feeling deeply the importance of calling the atten-
tion of the reader to an element which we regard as of

c^

vital importance, we have accordingly done so at the
risk of being somewhat tedious.

POSITION OF OBSERVER.

Our experience is, that in sixty cases out of the hun-
dred, having made some preliminary examination of an
object under study, and thus demonstrating the neces-
sity of the use of higher amplifications, that with the
latter comes also the necessity of a long and protracted
sitting ; in fact a downright seige is inaugurated. It is
better in all such cases to postpone work until evening,
or at least so to arrange that the observer shall have
perfect immunity trom interruptions of any nature;
and at the commencement of such work it is of para-
mount importance that the operator adopt such a posi-

POSITION OF OBSERVER. 247

tion at the work table as will allow him to observe for
hours without serious fatigue. Such a table as has
already been recommended, with two front drawers,
will be just what is wanted. The novice is here re-
minded that in working- with the higher powers, after
having placed the object in position under the objective,
the latter being correctly adjusted, there will be no
longer use for the coarse adjustment. Having, then,
our table, place the chair adjacent thereto, but in place
of putting its front edge parallel to the front of the
table, as is generally done, turn the chair to the right
until the front and left-hand sides form equal angles
with the front of the table, the angular point formed
by the meeting of the front and left-hand edges of the
chair being adjacent to the table. Now let the observer
seat himself, placing the shank of the left shoe on the
left-hand round of the chair. Pull out both drawers,
so that the edge of these, assisted by the edge of the
table, shall form a double rest for the forearm. Now
place the stand in such a position, that is, with refer-
ence to the front of the table, that the left hand finds
its way easily to the fine adjustment, while that of the
right grasps the mirror bodily, the tube being mean-
while adjusted to the standard length, and the whole
instrument properly inclined. Let the reader practice
these directions thoroughly until he shall be able to
thus sit at his instrument firmly wedged to it. It will be
noticed that, once in this position, either hand can grasp
the object slide for the purpose of making any neces-
sary change, and without seriously disturbing the double

248 HOW TO SEE WITH THE MICROSCOPE.

adjustment for the forearm, while the right hand, being
thus so nicely supported, is enabled to manipulate the
mirror with almost mathematical precision. At the
first, as might easily be supposed, the sharp edges of the
table and drawers will be a source of some little incon-
venience. This can be remedied by placing a pair of
napkins thereon; but the better way is to endure this
slight annoyance for a little time, when the forearm
will be found to have adapted itself to the situation.
The position thus described we have represented as far
as possible in the frontispiece, using such furniture as
was at hand in the photographer's gallery

This pose can be varied at times by bringing the left
knee in use so that it may support the left elbow. Thus
we get three rests lor the left arm, and sometimes we
get the shank of the right foot on to the front round
of the chair, spreading the knee open a bit and wedging
it under the right hand draw. Other little changes are

c5 O

practicable and need not be detailed here.

Of all the manipulations connected with the use of
the higher powers, the adjustment of the objective (sup-
posing, of course, that it is a good one, one that will
respond to the collar adjustment), is of paramount im •
portance. For reasons previously stated, two elements
are involved, namely, the behavior of the object glass
and the education of the eye ; and here the use of the
diatommecse is imperative. We have insisted on this
for years. These little organisms are the most con-
venient, and then, again, any little deviation from the
perfect correction of the objective is sure to " stick out "

POSITION OF OBSERVER. 249

and be detected. This is not the case with other objects.
Show the tyro a scale of podurse under a tolerably nar-
row angled one-tenth, and likewise display the same
with a similar object glass of the higher balsam angles.
There will be as much difference in the quality of the
two exhibits as there is (I was going to say) between
light and total darkness ; and yet, nevertheless, the nov-
ice will be as well satisfied with the one as with the
other; but let the experiment be repeated, using in the
place of the podura a balsam mount of surriella gemma,
both glasses doing their best, as before, and the tyro is
no longer " at sea " as to his choice. Moreover, at this
stage of his experience he will be fully prepared to blow
his trumpet in the support of one of the most absurd
and stupid errors that has ever been promulgated since
the time of Adam, to wit, " High angled glasses are only
fit for work over diatoms! !"

When we say that diatoms are the most convenient
objects over which to study the adjustment of the ob-
jective, ive mean it, and thereto attaches greater force
than the casual reader may suppose. If it be imagined
that these objects are " convenient" because their gen-
eral proportions are about the thing — because they can
be purchased at slight expense, or, if preferred, pre-
pared by the observer himself, or even be it granted
that the markings on the more difficult of these shells

i"5

will only surrender to a first-class objective in perfect
adjustment, we admit the facts, but the story is not
fully told.

The grand, the culminating convenience attending

250 HOW TO SEE WITH THE MICROSCOPE.

the use of diatoms in the study of the objectives used
under high amplifications, is this : We are enabled to-
display on one and the same mount, shells of the same
family and species, differing only in size, and we thus-
are on the instant ready to study the work of the ob-
jective over each. Now if it so be, and we make it a
point that it shall so be that the smaller shell is in all
respects the more difficult of the two. Then it occurs
that the student, having mastered such smaller frustule
can examine at his leisure the larger ones, and with the
certainty that his objective is in at least approximate
adjustment ; hence he is further prepared to note the
difference in the behavior of the object glass over the
different diatoms, and thus he arrives at items of the
utmost value; all this, too, without any change of the
mount.

Still other conveniences there are attending the use
of the diatom, their extreme thinness preventing the
shadow of one shell from interfering with the defini-
tion of another, thus getting rid of a complication
which would prove of serious detriment in the early
studies of the student, while by and by he can essay an
attack on the very problem named by merely selecting
sueh positions of the amount as contain the little
organisms huddled together. Thus learning their char-
acter and being thus forewarned, is fore-armed against
the time when he shall be brought in contact with
other slides presenting the same difficulty, but in a
more determined manner.

But let the reader note this fact. It is one thing to

POSITION OF OBSERVER. 251

look at diatoms, and quite another to study them with
the especial object of becoming acquainted with the
behavior of the objective, while it must be admitted
that there is a fascination and charm per se, connected
with diatom examinations under the microscope. It is
equally true that the student can use them legitimately
and for the purpose named, without establishing any
claim to the functions of the diatomist.

Referring to the especial purposes we have been con-
sidering, the following list of objects will amply suffice,,
for the study of the one-sixth or one-tenth objectives,,
viz:

1. Navicular Rhomboides, Monmouth, Maine, Balsam Mount

2. Navicular Rhomboides, Cherrytield, Balsam Mount.

3. Frustulia Saxonica, Leipsig, Germany, Balsam Mount.

4. Frustulia Saxonica, Isle of Shoals, U. S., Balsam Mount.

5. Amphipleura Pellucida, Bridge of Allan, Scotland, Balsam

Mount.

6. Amphipleura Peliucida, Aberdeen, Scotland, Balsam Mount.

7. Surriella Gemma, Balsam Mount.

Of the above list, Nos. 1 and 2 can readily be ob-
tained of the dealers. As to the others named, Prof.
H. L. Smith, of Geneva, N. Y., has a large supply of
the material, and has kindly supplied the author and
his friends with excellent mounts and at figures much
below the usual list prices.

In addition to the diatoms, a genuine mount of
English podura will be a capital thing to have on hand
for occasional comparisons, but the student must on no-
account select the slide himself. Poor scales are simply
good for nothing, while perfect ones are held by the
opticians in the highest esteem, and are constantly used

252 HOAV TO SEE WITH THE MICROSCOPE.

by them in the final corrections of the objective. Of
all the scales of podura we have yet seen, a mount was
shown us last summer by Mr. Herbert Spencer, which
was perfection itself. As an index of the value Mr.
Spencer attached to this mount, I will add that he had
once offered one of his first class one-tenth objectives
in exchange for it !

Every microscopist needs a suitable stage micrometer
and very lew have reliable ones. We gladly state that
Prof. W. A. Rogers, of Cambridge, Mass., has after
years of careful study succeeded in making rulings on
glass rivaling if not excelling those of Nobert himself.
Not long since Prof. Rogers ruled for us a plate, con-
taining lines 100, 1,000, 2,000, 5,000, 10,000, 20,000,
40,000 and 80,000 to the inch, which was a marvel in
point of accuracy and delicacy. Subsequently Prof.
Rogers ruled a plate for us up to 120,000 lines to the
inch. This band the author has seen well and has
shown to his friends. We therefore recommend first,
that every student should be possessed of a micrometer;
-and secondly, that the same be procured from Prof.
Rogers. It will be well while one is about it, to order
a plate ruled as high as 80,000 to the inch, inasmuch as
the cost is not materially enhanced, the plate will thus
do double service not only as a stage micrometer, but
as a test plate for the comparison and study of objec-
tives. In this connection the reader will remember
that we have advised that eye-piece micrometers be
ruled. GOO lines to the inch. Hence, if our advice is
followed, let the stage micrometer have a similar band.

POSITION OF OBSERVER. 253

The positive convenience resulting1 from this in the
measurement of the focal length of objectives by the
method previously described is too obvious to need
further comment.

The series of graduated diatoms by Moller of Wedel,
Germany, and generally known as the Moller test
Plate, is now to be found in the cabinet of nearly
every microscopist, and can be advantageously supple-
mented to the list above given. A table showing the
mean of the measurement of ten of these plates will
be now furnished and thus the plate can on a pinch be
made to do approximate duty as a stage micrometer.

MEAN OF TEN MEASUREMENTS OF MOLLER TEST PLATES,,
BY PROF. E. W. MORELEY, M. D., OF HUDSON, OHIO.

1. Triceratium Favus 3.1 to 4.

2. Pinnularia Nobilis 11.7 to 14.

3. NaviculaLyra 14.5 to 18.

4. Navicula Lyra 23.0 to 30.5.

5. Pinnularia Interrupta, 25.5 to 29.5.

6. Stauronesis Phoenicenteron 31. to 36.5.

7. Grammatophora Marina 36. to 39.

8. Pleurosigma Balticum 32. to 37.

9. Pleurosigma Acutninatum 41. to 46.5.

10. Nitzschia Amphoyx 43. to 49.

11. Pleurosigma Angulatum 44. to 49.

12. Grammatophora Oeeanica=G. Subtilissima 60. to 67.

13. Surriella Gemma 43. to 54.

14. Nitzschia Sigmoidea 61. to 64.

15. Pleurosigma Fasciola 55. to 58.

16. Surriella Gemma. Longitudinal 64. to 69.

17. Cymatopleura Elliptica 55. to 81.

18. Navicula Crassinervis, Frustuiia Saxonica 78. to 87.

19. Nitzschia Curvula 83. to 90.

20. Amphipleura Pellucida 92. to 95.

254 HOW TO SEE WITH THE MICROSCOPE.

THESE FIGURES DENOTING THE NUMBER OF LINES IN .001
OF AN ENGLISH INCH.

As a matter of convenience to those having the cele-
brated Nobert 19 band test plate, we present the fol-
lowing tabulated values of the rulings. The first
column contains the value in Paris lines. The second
the number c f lines in .001 of an English inch, as ruled
in the several bands.

NUMBER. PARIS MNES. IN .100 ENO. IN.

1 1,000 11.26

2 1,500 16.89

3 2,000 22.52

4 2,500 28.13

5 3,000 33.78

6 3,500 39.41

7 4.000 45.04

8 4,500 50.67

9 5,000 56.30

10 5.500 6! .93

11 60ao 67.56

12 6.500 73.19

13 7.000 78.82

14 7,500 84.45

15 «,000 90.08

16 8,500 95.71

17 y,000 101 .34

18 9,500 106.97

19 10,000 112.60

Returning now to our original list of diatom mounts
we proceed to give such a description of the sumo as
will enable the student to approach them intelligently,
iind without undue loss or waste of time. The first two
slides are pretty much the same thing, both contain

POSITION OF OBSERVER. 255

tine shells of navicular rhomboides, and nicely assorted
.as to size and "difficulty." The larger, or even the
medium sized shells are easily displayed (we refer to
the transverse striae) by such a glass as the Spencer dry
•one-fourth of 115°, when nicely adjusted, while the
smaller- frustules are more "difficult" tha a the No. 18
of the Moller plate. These mounts are therfore valu-
able on account of their range, and the reader has
already our reasons governing the selection thereof.
When these slides are thoroughly mastered, the student
will be ready to attack the Saxonica from Leipsig.
These vary also, a medium shell being about as obsti-
nate as the No. 18 of the Moller plate, and will defeat
the Spencer one-fourth. The Saxonica from the Isle
of Shoals is still more bothersome. These frustules
are very small i.nd very thin, and at the start the
student should select the very largest and most vigorous
shell he can find on the mount, proceeding carefully as
he may acquire skill, to the smaller ones, and before he
can establish any claim to have mastered this slide he
must be able to show the very smallest and thinnest
shell acceptably. In point of "difficulty" these smaller
diatoms rival the No. 19 of the Moller plate, while the
smallest and the very thinnest are a fair match for the
No. 20. Of the amphipleuras, that from the " Bridge
of Allan," Scotland, is the easier of the two, and
should be studied first. This slide in common with the
two last mentioned calls for object-glasses of high
apertures. To attack them with any of the low angled
glasses is but a waste of time and patience. The mount

256 HOW TO SEE WITH THE MICROSCOPE.

of surriella gemma is selected for reasons very much
akin to the mention that has been made of podura.
These shells are not suited for the purpose of study,
but are admirably adapted for comparisons. The
actual structure of this diatom is yet a matter sub
judice.

Now let us go back again to the first mounts named
in the list. We have had occasion before to assert that
one of the advantages resulting from the study of di-
atoms is due to the fact that the student in mastering
one of the smaller and more difficult ones becomes
fortified as to the adjustment of his glass. Supposing
then that by some good luck he has succeeded in dis-
playing the smaller frustules of the Monmouth or
Cherryfielcl. He can return to the larger shells with
tolerable. assurance that his glass is in fair correction.
But mark this. In order to show the little fellows,
there was need of greater obliquity of illumination,
which, when return shall be made to the larger shells
can profitably be dispensed with. Now although the
slide of diatoms offer special conveniences, let the
student adopt this line of study, no matter what may
be the character of the object under his objective, select-
ing the most obscure and diaphanous structure possi-
ble to bring into the field, and making sure that there
is a sufficiency of oblique illumination.

From what has been said it may be adduced as a gen-
eral rule that it is advisable to study the corrections of
the objective by the aid of oblique light, and over the
finest structure the mount can be made to exhibit, and

POSITION OF OBSERVKll. 257

to the beginner no better advice can be given. It is
simply impossible for the novice to study the correc-
tions of a high angled object-glass by centrally disposed
illumination.

In the selection of the ohjects recommended to the
student, we have been governed by these and similar
considerations. All of the slides named contain frus-
tules requiring the use of light at least 40° from axis,
and the student will in his first attempts be compelled
to go considerably higher than that tigure. The exact
amount of obliquity essential to the best display he can
possibly make, will depend on his object-glass the cor-
rectne&s of its adjustment, and the education of his
eye.

We shall, on some succeeding page have a few words
to say as to the management, etc., of high balsam
apertures by centrally disposed light. With this one
exception only, anything that we may have to offer in
the way of instruction bearing on the use of these
glasses will be confined to the study of the diatoms
which have been presented. The student who can
properly display the seven mounts to which his atten-
tion has been invited, together with the Moller plate
and the poclura, can safely be allowed to shift for him-
self. We, however, fear that our ability to teach this
much will not now keep pace with our sincere desire.
Competent, or incompetent, we propose to try. A
singular fact it is, that among all the works thus far
written on the microscope not one word of instruction
can be found as to the management of objectives of

Microscopy 17

258 HOW TO SEE WITH THE MICROSCOPE.

wide apertures. It is therefore high time that some
one kt assume the judicial." Any endeavor on the part
of anyone to teach the management of wide apertured
object-glasses must in the nature of things be incom-
plete, and at the best but approximative. Notably so
as to written instructions, no two objectives work
exactly alike, and appearances in the field will be mod-
ified by the individual corrections of the particular
glass employed. Of two objectives, one may be supe-
rior to the other. Hence the student not being a con-
noisseur becomes environed with doubts that the ex-
pert might easily cause to vanish by a little personal
interference. Object-glasses, too, wcrk differently over
different objects. The appearance of a dry mounted
object is characteristically at variance with the appear-
ances presented by balsam mounts, and here is our
reason for selecting in every instance the latter for the
instruction of the beginner. Neither is it possible for
the professional philologist by mere force of word pic-
turing to convey to the mind of the learner just what
may be desired. And even should the teacher be fortu-
nate enough to employ the most accurate descriptions
language can afford, then he has no assurance of being
perfectly understood by the pupil. The author being
no philologist, and having but a little command of
language desirous of using none other than the simplest
words, thus adapting this little book to the compre-
hension of all, can but essay his best and only hope for
partial success.

A word or two further before we proceed with our

POSITION OF OBSEKVEK. 259

tuition. The remark is often of late made, "what does
all this talk about the handling " of objectives mean?
Are we to understand that the real work of the micro-
scopist consists in the resolution of a few diatoms, or
the exhibition of the rulings of the l9thNobert band?
To this we reply, that all this is implied and a very
great deal more ; it means that the microscopist shall
know as much of the microscope as it is expected of
the engineer to know of his level or transit. In

O

geodesy the value of entire systems of costly triangu-
lations are wholly dependent on the accuracy of the
original base line, and in a similar manner is the work
of the microscopist affected. We often hear old ob-
servers claim that all work worth having with the
microscope is accomplished with amplifications less than
300 diameters ; and then again the scientific contribu-
tions resulting from the use of the finest English objec-
tives in the hands of physicists like Professors Tyndall
and Huxley dependent on amplifications of 5,000 and
6,000 diameters, have been seriously called in question,
yea, disputed by those working with objectives not
worth the weight of their brass mountings! We
repeat, that it is eminently the business of the would-
be microscopist to know all that can be known of his
instrument; if, when he has to an acceptable extent ac-
quired this knowledge, if so be that he prefers not to
devote his time and microscope to investigation, he has
the satisfaction of being conscious that what was done
was well done. Had the engineers employed in meas-
uring the original base on which the coast survey was

260 HOW TO SEE WITH THE MICROSCOPE.

founded, chosen to have abandoned the work on the
completion of the base, there would have been no time
lost or wasted; per contra, had the base been but im-
perfectly measured, and the engineers proceeded to
build the other triangles resting thereon, they would
not long have continued in the service, but would have
been furnished with palpable reasons for leaving!

Again, the question is ofttimes asked, do you require
that the observer shall be familiar enough with his ob-
jective as to work it up to the same force as its maker
could? Its the legitimate business of the optician, and
he can thus afford to spend his time on a matter which
to him is a necessity, but to demand this much of the
practical observer seems uncalled for. In answer to
this oft-repeated remark, we wish it distinctly under-
stood that it is eminently the business of the observer
to fully understand the practical woiking of his objec-
tives. The man who cannot make his object-glass per-
form as well as when in the hands of its maker, is using
an instrument that he does not fully understand, of
which the fact becomes incontestible proof. If it be
necessary that the optician be able to work an objec-
tive to its maximum, it is imperative that the micro-
scopist should do as much. Until this shall be the
case, absurdities will abound. Take for instance a con-
dition that often occurs. The microscopist orders a
new objective from the optician. The specifications are
complete, and the glass is made conformably thereto.
In due time the purchaser receives his glass, and can do
nothing with it, and it is returned in high dungeon to

POSITION OF OBSERVER. 261

its maker. And why? Simply because the purchaser
was as incompetent to " handle " the instrument, as
perchance he might have been to manipulate a piano-
forte or church organ. And then again through his
ignorance he might have possibly ordered the very
ffltiss he did not want. What would we sav to the

<5 »/

invalid who on summoning the attendance of the physi-
cian should undertake to dictate as to the treatment!

Again, we have often been requested by our friends
and visitors to examine objectives and give our opinion
thereon ; and, as a rule, five minutes will suffice for this.
But, says the owner, "you must be prejudiced against
my glass. Xo man could give a well grounded opinion
in the few moments you have occupied." Nevertheless,
we have given hundreds of just such opinions without
having had occasion to modify or retract, and here is
an illustration showing that time spent in the study of
objectives is neither totally lost nor without its compen-
sations. We reiterate, let the microscopist understand
well his tools, and in the hope of being at least some
assistance to the student we are ready to proceed with
our instructions.

In the lessons which follow the reader is presumed to
•employ a wide apertured one-fifth, one-sixth or one-
tenth immersion. We shall try, as far as possible, to
make them applicable to the use of any good glass hav-
ing air angle up to 175°. The higher balsam angles
will, however, when attainable, be the better instrument,
with which, too, the instructions will be the better un-
derstood. The student is also reminded that with the

262 HOW TO SEE WITH THE MICROSCOPE.

particular objective he may employ he may be in some
measure defeated in his efforts ; still we have to hope
that his endeavors will not result in time " totally
lost."

Lesson First. — Place the mount of Monmouth rhom-
boids on the stand, select the two-inch ocular, mak-
ing immersion contact with water or glycerine, as has
previously been directed. Place the collar of the ad-
justment in the middle of its run; use the light from
the smallest kerosene hand lamp, placing the same about
seven inches to the left of the stage, the flarne to be on
a level with the same, edgewise to the mirror, and two
inches in advance of the front edge thereof. Removing
all sub-stage appliances, swing the radial bar so that the
mirror shall give illumination, say from 70° axis; ma-
nipulate so as to light up the field, using about one-half
the sized flame your lamp will allow. Now focus, and
having taken a general look at the " tout ensemble,"
select a frustule somewhat below a medium one in size,
and bring to the centre of the field, the valve in a hor-
izontal position. Now focus a«:am carefully, adjusting
the mirror so as to get the very best view attainable.
Now study for a moment the general character of the
image. Notice particularly if there be any distortion,
or whether the two ends are more or less indistinct or
obscured. Slide the object carrier and hunt up several
other shells and examine individually, that 3 ou may be
assured that you have a fair specimen to deal with.
Next, notice the edges of the valve; compare the upper
with the under; note if these are tolerably clean and

POSITION OF OBSERVER. 263

sharp, or whether they are more or less woolley. Com-
pare the median line with the upper and lower edges.
Manipulate the fine adjustment and notice as to any
change of focus necessary as between the edges and the
median line; study this median line well, and you will
probably detect a shadow from it shading, but only per-
haps slightly, the lower entire half of the shell. Grasp
the mirror firmly and change its position (not the radial
arm) a little in every direction, meanwhile studying the
effect of the shadow on the lower half of the frustule.
Hunt up other frustules and study them in like man-
ner, changing the focus from time to time as may be
necessary.

Selecting an average shell, and placing the same in
the centre of the field, and focus sharply. Having ar-
ranged the mirror to the best advantage, grasp the collar
of the objective with the fingers of the right hand
(which now leaves the mirror just as it was), those of
the left hand being in contact with the fine adjustment,
withdraw the eye for an instant and turn the collar of
the adjustment briskly nearly a full half revolution ;
placing again the eye in position, focus quickly and
sharply. Now undertake to decide instantly as to the
effects produced." Is there more or less distortion at
the ends of the shell than before? How are the edges?
Cleaner and sharper, or the reverse? How is that
shadow below the median line? Does it shade the en-
tire half of the valve more than was the case formerly,
or has it consolidated itself to a narrow band under the
median line? If you find the least trouble in assuring

264 HOW TO SEE WITH THE MICROSCOPE.

yourself instantly, repeat the programme until you can.
Now, reader, one-half hour conscientiously spent at this
exercise will assist you more than a half year of pro-
miscuous practice. Let me advise you to hang well to
it. You must learn to judge instantly as to the appear-
ances to which your attention has been called, nor can
the least " guess-work" be allowed.

Well, now, premising that you have had sufficient of
this practice, so that you are able to assert, without fear
of contradiction, that after the turn of the collar adjust-
ment, there was, as we will assume, evident!}7 more dis-
tortion noticeable at the ends of the valve, nor were
the edges as sharply defined, (it may be that one edge
cannot now be seen without specially focussing therefor. N
The shadow, too, under the median line is not only en-
tirely over the entire lower half of the shell, but it has
become deeper and more offensive than before. The
fact, then, becomes apparent that you turned the collar
in the wrong direction. Therefore, place the adjust-
ment in its original position ; look your shell well over,
thus to fortify yourself.. It will be well, now, to repeat
the experiment, selecting various valves of the rhom-
boicles, and, having become accustomed to the change
in appearances, then you may try many of the other
diatoms to be found on the mount. No matter what
particular one may be selected, you will in due time be
able to note the characteristic effect of this change in
the adjustment.

Lesson Second. — Having replaced the collar adjust-
ment to its first position, and selecting a tolerably small

POSITION OF OBSERVER. 2ti5

shell of the rhomboides, place it in the centre of the
field, the focus well adjusted, etc. Devote a few mo-
ments to a general consideration of the nature of the
changes wrought by the turn of the collar. Endeavor
to gather up, as it were, the experience gained by les-
son first. This done, removing the eye for a moment,
turn the adjustment in an opposite direction to that of
lesson first, but not so far in extent, and immediately
looking through the tube, adjust again the focus, and if
necessary adjust also the mirror until the best view of
the shell shall be obtained.

Now if the preceding lesson has been well studied, the
learner ought to recognize a decided improvement, and
there ought, withal, to be more general brilliancy to the
image. The shell should, so to speak, lay flatter in the
'field. In short, things ought to assume an encouraging
•appearance. Repeat the experiment several times, but
with greater or lesser changes of the collar adjustment,
until you arrive at a particular point in the adjustment
which seems to be about the thing. Having thus deter-
mined this point, the student may now, by way of en-
•couragement, shift the position of the object carrier
and bring one of the larger shells to the centre of the
field, when, with a slight alteration of the mirror, he
will probably be rewarded with a fair view of the trans-
verse stria?. Assuming this to be so, let the student
examine progressively other and smaller frustules, and
selecting one of the very smallest that he can see, bring
it to the centre of the field.

Wesson Third. — Replace the collar to the initial po-

266 HOW TO SEE WITH THE MICROSCOPE.

sition, as per lesson second, focus your new shell and
examine it critically, as has already been directed ; next,,
repeat the turn of the collar, in the same direction, but
varying" the extent of the movement, focussing1 again
as before. Bye-and-bye, when the collar shall have been
turned to approximately the correct place, the strifie will
of course be again visible, and it is more than probable
will be even better seen than before. If this shall be
the case, try, by slight manipulations of the mirror
alone, to obtain the very best display of the lines. And
we now approach close work. If the eyes are tired, or
the general condition of health be below par, it will be
better, if any further work be determined upon, to go
back and take a review of what has already been accom-
plished; but on the other hand, if conditions are gen-
erally favorable, proceed thus :

Lesson Fourth. — With your frustule as nicely exhi-
bited as possible, the shell selected being as small as you
can successfully attack to show well the stride, examine
it well closely; see if the upper and under edge are
both equally well in focus. It may be that one edge is.
much better denned than the other, or it may be that
one edge cannot be seen at all. This indicates that the
valve lies sidewise in the balsam, in which event discard
the shell and hunt up another that lies exactly flat, and
of the same size.

Now work over this diatom, generally as you have
been instructed in the foregoing lessons, accepting the
position you now have of the adjustment as the base of
farther trials. Change the collar to the right or left*

POSITION OF OBSERVER. 267

noticing" all the points to which your attention has been
called ; but these various changes of the collar should
be much less limited in extent. We have now further
items for you to observe. Examine the since carefully;
see if they continue quite to the edge of the shell, or do
they stop a little short thereof, the edge becoming as
clear, sharp and distinct as that of a razor. Look with
an eagle eye, too, into that shadow under the median,
line. Has it become almost self-luminous and trans-
parent? And has it drawn itself upwards and together r
forming a narrow but brilliant band (so to speak) ad-
jacent to the under side of the median line? Have all
appearances of diffraction lines left? Does the shell lay
well down and flat? All of these interrogatories must
receive your devoted attention.

When things are just right, the valve laying flat in
the balsam, the striae will not quite extend to the edge
of the shell. The dark band under the median line
will be contracted as described, but in the place of the
former dark and muggy shadow, it will have become
lively and brilliant. Ditto, as to all the other shadows-
seen in the field. In fact, everything has improved, be
it a diatom or a patch of dirt. The edge of your shell
ought to be sharply distinguishable, not by a line of
varying thickness, for there is no line there, and there-
fore you ought not to see anything of the kind. If the
adjustment be a trifle out, it will sometimes occur that
the valve will seem to "rise up;" i.e., appear nearer
to the eye than it should. It is impossible to describe
on paper just what I mean by this. I have no trouble,

268 HOW TO SEE WITH THE MICROSCOPE.

however, in getting pupils to appreciate this phenome-
non. This effect is the more palpable under a high oc-
ular, say the one-fourth inch. Let the student try the
highest one he has, and he will notice that a slight chancre

<^ DO

of the collar will cause the shell to " lay down " prop-
erly. But he must nevertheless be able to make this
correction from noticing the condition when employing
the two-inch eye-piece, And here it may be observed
that with different objectives some leeway must be
allowed. It is hardly probable that the student can
take his particular object glass and follow me to the
very letter; or is it even certain that the author could,
with said glass, demonstrate to an expert what has been
written in these instructions ; yet after allowing due and
proper margin, the hints presented must prove of value,
and if we could have been told as much eight years ago
it would have saved us hours and hours of the toughest
work. And right here a thought presents itself, for-
eign, perhaps, to these lessons, but let it go on record,
namely : If it be so that we can assist the student, we
have in very truth no mean reward for time spent in
the past in the study of object glasses.

Lesson Fifth. — Having noted the division correspond-
ing to the exact adjustment of your objective, so that
you shall be able to place the collar at the right spot at
-once, without loss of time, leave the rhomboidcs and
•examine your mount generally. Notice the play of light
and shade over the several diatoms. Hunt up those por-
tions of the slide containing a mass of the larger forms
huddled together; in other places you will probably

POSITION OF OBSERVES.

find sediment congregated together in little colonies, the
coarser particles throwing an individual shadow over
the others. Observe these appearances closely. Now
place the collar intentionally out of adjustment (prefer-
ably opening the systems), and thus look over your
mount again. See, how the shadows have become mixed
up! What a labyrinth there is to be sure! A perfect
plexus of indeterminable, indefinable shadows proceed-
ing from nowhere and ending nowhere. The thickened
edges of the diatoms seem to cast a shadow on their
own account. Notice, too, how that some of these
large shells seem to have become badly distorted. Find
those little colonies again, and note that the individual
particles thereof have lost their brilliancy — have become
muggy and indefinite. Here, too, are all sorts of shad-
ows, and more or less confusion generally. Return,
now the collar to its proper place and review your
mount. Now, see how things have improved in general
brilliancy ; see how the shadows have become harnessed
properly into the traces. You can trace them now, and
get an idea of what they mean, where they came from,
and where they end. Look at the little colonies once
more. Now they are all alive with brilliancy and sparkle
like very diamonds.

When the student feels that he can follow me thus
far, let him study the tone of his objective. This will
depend on the object-glass employed. All superfine
objectives should be under corrected, i. e., there should
be a preponderance of the blue; but hardly any two
good objectives are exactly alike, some being under-

270 HOW TO SEE WITH THE MICROSCOPE.

•corrected to a greater extent than others. Whatever
may be the correction of a given object-glass, there
will be a corresponding tone to the field, and it's the
business of the learner not only to know the fact but
to be competent to recognize the characteristic appear-
ance presented not by the particular object viewed
alone, but by the entire field of view. And here again
comes some nice eye work. The artist can look at the
landscape and recognize the very "atmosphere" — not
so the shepherd's boy. The former might talk until
dooms-day to the latter as to *« atmosphere."

Now every good object-glass has an "atmosphere"
of its own, peculiar to itself, and depending on the
individual corrections of the glass. A moment's con-
templation of the situation teaches the difficulty attend-
ing any effort on the part of the author to make him-
self understood so as to be of service to the learner.
Nevertheless, the attempt shall be made.

Lesson Sixth. — Place the shell of rhomboides exactly
in the centre of the field, and adjust the object-glass.
Arrange the mirror with its radial bar, so as to illumi-
nate at about 45° or 50° from axis. Focussing sharply,
examine well your diatom as to color; the chances are
that both blue and red are to be observed. Select in
turn several shells and thus examine, and finally in-
spect all the objects on the mount before mentioned.
A little patient attention will teach you that there is
something apparently due to the blue that docs not
attach to the red. For instance, the shells may have a
slight lavender tint; as soon as one can detect any-

POSITION OF OBSERVER. 271

thing in this way that is presumed to be characteristic,
then put the object-glass out of adjustment and focus-
sing anew make the comparison. If the student has
hit the proper effect, he will notice that with the glass
out of adjustment, said effect has vanished. Should (as
will most probably be the case with his first efforts) he
fail to mark any characteristic Sifference in color or
tint, replace the collar adjustment and repeat the ex-
periment; selecting, as near as he can judge, some
" probability," and again throwing the glass out of
proper adjustment examine again. The process must
be repeated time after time until the end shall be
gained. When by dint of practice the learner begins
to feel that he " sees the point" let him in a similar
manner examine all of the other diatoms on the mount
until he shall have become perfectly familiar with the
lone of his objective.

Lesson Seventh. — Having mastered tolerably well the
previous instructions, let the learner now turn his atten-
tion to the tone of his field. This is a finer "point"
than that of the preceding lesson, and demands in turn
more of the eye-training. The problem is in all
respects similar to that concerning the tone of the
objective, differing in this one element only. The
student must now endeavor to recognize a particular
tone to the whole field when the object glass is in per-
fect adjustment. The instructions are quite of the
character as those of the last lesson, an 1 need not be
repeated. The two lessons might have been reduced to
, were it not that a little practice on the former

272 HOW TO SEE WITH THE MICROSCOPE.

will, and for the reason named, be advantageous before
studying the tone of the field. These last two lessons
should not only be well studied, but the student ought
constantly to endeavor to improve in his recognition of
tone. Once having become tolerably, I may say, com-
fortably expert, its practice becomes a second nature
and will be persisted* in from choice, meanwhile the
observer becoming daily more and more proficient.

This characteristic tone of the field is more apparent
in objectives of the highest balsam angles, with the
super-excellent object-glasses of the Messrs. Spencer or
Mr. Tolles, when the glass is exactly in correction, the
tone of the field becomes a peculiar and exceedingly
delicate shade of apple green, which one soon learns to
recognize by aid of the teacher.

In the studies we have thus far presented, and which
ought to enlist the occasional attention of the pupil for
at least a month or six weeks, it is taken for granted
that he will meanwhile use the instrument as he may
elect, and either for pleasure or such profit as he can
arrive at on his own account. There will undoubtedly
be other objects brought into requisition not named in
our lists. Now, whatever practice he may have of this
description, there are some general conditions concern-
ing high-angled objectives which ought not to be un-
heeded, for example, let the learner discover as near as
possible the point ot the maximum aperture of his
glass ; it will be well, too, that he pay attention as to
thickness of the covers used. These two points have a
direct bearing on the pupil's progress and must not be
neglected.

POSITION OF OBSERVER. 273

Hand the expert a strange mount of the Monmouth
or Cherryfield rhomboides. It is possible for him with-
out looking at it, and by the sense of feeling alone to
state thus : " This slide cannot be used with the one-
tenth and glycerine contact. Use water and with the
collar nearly at closed. If the one-sixth be employed
use glycerine, and the objective will correct within
four or five divisions from the closed point." Either
statement being found on the actual test or trial to be
the fact. In truth, any such statement from the expert
founded on his sense of feeling alone would be worth
more than two hours spent over the tube by the novice.
Hence the importance of the learner's acquiring the
same tact (" knack " is the popular word), nor is there
anything so very difficult in its acquisition.

Lesson Eighth. — Returning to the slide of Monmouth
Rhomboides, and choosing a frustule somewhat larger
than a medium one, place it in the centre of the field,
adjusting the objective, and displaying the striae, em-
ploying an obliquity of say 70° from axis. Next rotate
the stage through an arc of 45° ; if necessary centre the
object again. It will now have assumed a position in-
termediate between the horizontal and the vertical.
Attempt, by slight changes in the position of the mirror,
to display simultaneously both sets of lines. The inch
ocular may now be substituted in place of the two inch.
To do this nicely, getting both sets with equal force,
requires indeed some little "knack." The collar ad-
justment being already correct, the manipulation will
entirely be confined to the illumination. Possibly it

18 Microscopy.

274 HOW TO SEE WITH THE MICROSCOPE.

may be well to shove the lamp a little farther away from
you; i. e., a little more in advance of the front edge of
the stage, or perhaps raising or lowering the wick, thus
increasing or diminishing the amount of light, may be
of service. This is all that can be written, and the
learner must simply make the most of and help himself.
Rest assured that both sets of lines are there, and
if it be that they are not shown, the diatom is not to
blame. In case of total failure the observer may select
one of the larger shells, proceeding to the smaller one?
carefully and by degrees. With the illumination at
present employed he cannot expect thus to show both
sets on frustules smaller than a medium one. After
having mastered, as well as may be, the Monmouth,
substitute the Cherryfield, readjusting the objective, as
a matter of course.

There now remain, for future consideration, on the
slides of Monmouth and the Cherryfield, the smallest
frustules of the rhomboides. These we will pass over
for the present, and in the next lesson proceed to attack
the Saxonicas, from Leipsic, Germany.

Lesson Ninth. — The student will recognize the frus-
tules on this slide by their similarity to the two slides
preceding. The valves are on an average smaller and
thinner, and in consequence weaker objects to deal with ;
as the saying is, they are more " difficult." Select one
of the largest and most vigorous shells ; bring to the
centre of the field, and, employing the inch ocular, focus,
the illumination being about 70° from axis. Now ex-
amine closely your diatom, and see if you can bring

POSITION OF OBSERVER. 275

your past experience to bear. Without attempting to
observe as to the striee, reckon up the general appear-
ances and form some verdict as to whether the glass is
in adjustment. If you decide that it is not, make up
your mind to what extent. This done, proceed, if ne-
cessary, to adjust, following the directions already given,
bearing now in mind that all the phenomena previously
described will be much fainter and less decided than was
the case of the Cherryfield or the Monmouth.

Let the student assure himself that the shell before
him lays perfectly flat in the balsam. If this is not the
case, it will be impossible to see both the upper and
under edges simultaneously. These frustules are ex-
tremely thin, and when one edge is the lower of the
two in the mounting medium, it will appear to vanish
out of sight. Accepting that the diatom is a favorable
one for study, the learner will notice that the upper and
lower edges, as the adjustment approaches the proper
position, behave better than was the case with the Cher-
ryfield or the Monmouth. This is owing, of course, to
the diaphanous character of the Leipsic. He will there-
fore endeavor to render these edges considerably sharper
and cleaner than could possibly have been the case when
working over the former slides. Let the pupil observe
closely the behavior of the shadow under the median
line. As has already been remarked, the effects are quite
similar, but in a less marked degree. The eye must be
educated to the situation. Notice, too, that as the ad-
justment becomes more perfect this shadow contracts,
assuming the form of a narrow band immediately adja-

276 HOW TO SEE WITH THE MICROSCOPE.

«

cent to the median line, while the entire lower half of
the shell is of a lower tone than that of the upper.

Should the tryo have got along thus far tolerably
well, it is more than probable that he will have been
rewarded by at least a glimpse of the transverse strise.
He may now, by minute changes of the mirror, and by
raising or lowering the wick of the lamp, endeavor to
show the markings as strongly (that's a bad word) as
neatly as possible. Having thus succeeded, look sharply
and see if the lines extend quite to the edges of the
frustule ; it may be that some of them will be found to
project ; in either case something is wrong. Look first
to the illumination, and, observing the shadow line
under the median line, endeavor to contract and render
this as narrow as possible. If this does not prevent the
striae from showing to the extreme edges of this valve,
then recourse must be had to slight alterations in the
position of the collar adjustment. It may be advisable
to try a stronger ocular, say the " D " solid, if one is at
hand. If under this the lines seem to " rise," try and
correct this, as before instructed.

This apparent "rising" will perhaps strike the reader
as something novel. Certain it is that we have never
seen anything of the kind in print. The effect was,
however, noticed long ago by the author, and it soon
became one of his " points " in the tuition of his pupils,
the latter, at the onset, seldom ever get his meaning.
Nevertheless, in a very little time they " see it " plain
enough. We have not command of a word that will
precisely and accurately express what we desire. It

POSITION OF OBSERVER. 277

may be advantageous to the student if we repeat ejacu-
lations such as are heard from scholars, thus : " I can't
make this shell lay down." " I have a tolerably good
show, but the valve is restless.'"' " You seem to anchor
your diatoms; mine are all out at sea." "The valve
will float in spite of me." "I have it; the shell lays
as quiet as a summer morn." "This valve seems to
come right up to the eye-piece," (referring generally to
the one-half or one-fourth inch.) Such and similar ex-
pressions we have heard over and over again. The
student can select the one that will be of the most
service.

The tone of the objective should be studied with the
Leipsig, just as has before been noticed when discussing
the Monmouth and the Cherryfield. The observer may,
at the commencement, entertain the notion that in re-
gard to tone, the objective behaves very differently when
over the more difficult mount. If, however, the pre-
ceding lessons have become perfectly familiar there will
be but little trouble in recognizing the same peculiar
and characteristic tone not only pervading the valve,
but the entire field of the instrument.

Suppose, now, that the manipulator, having followed
the author with satisfactory success through the Mon-
mouth and the Cherryfield, should fail thus to do when
the Leipsig is taken in hand, thus : There appears a cer-
tain indistinctness accompanying .the images of the latter,
besides, the valves seem considerably distorted, and the
band of light behaves badly ; so much so that the direc-
tions cannot be followed with any degree of certainty,

278 HOW TO SEE WITH THE MICROSCOPE.

and that several trials have been ineffectually made ; all
of which lead to the same result. In this case the prob-
abilities are that the objective is at fault, and that any
attempt to work it by anyone, however expert, will
only result in a waste of time. The student ought not
to decide definitely until by practice he shall be entirely
competent to judge for himself. We mention the fact
here, because we know full well that some who may
read these pages will try and follow the author, employ-
ing such objectives as they may have at hand. Now it
might occur that an object glass capable of showing a
medium Cherry field or a Monmouth very well indeed,
even cutting the larger shells into checks or squares,
responding, too, to all the conditions we have presented,
and yet entirely fail when worked over any but an ex-
ceptionally large shell of the Leipsig.

It may be apropos here to discuss another point which
is suggested as we write: It will be noticed that all
along in the course of these lessons we have made it oblig-
atory that the simplest illumination shall alone be em-
ployed, reserving for the present any allusion to special
methods used in the resolutions of the severest tests.
Our reasons are patent. First, the little lamp recom-
mended is in ordinary use, and is always at hand when
wanted; as to its size, the small lamp is even superior
to a larger one, while the smaller model has the advan-
tage of burning less oil, is handier to manipulate, and
is the more portable of the two. In a former part of
the book we have acknowledged the superior force due
to modified sunlight; nevertheless, the latter is unfit

POSITION OF OBSZRVER. 279

for the everyday work of the microscopist. The ob-
server who depends thereon leans on a treacherous staff.
Could we command sunlight, this objection would cer-
tainly have less force; but even in that case we would
be compelled to fall back on artificial illumination in
the evening, and eight-tenths of all microscope work is
done after sundown. Hence it is of profound import-
ance that the microscopist select such illumination as he
can at all times control, and to learn to make the best
possible use of it. Again, all that we have said as to
sunlight applies with equal force to objectives that re-
quire to be worked with its aid. Let the reader note
well this fact. It has been our purpose here, as it is
every day with our pupils, to teach the use of the sim-
plest methods, both as regards illumination and other
items of management.

Keturning, now, to our diatom slides again, we remark
that the objective failing, with the stipulated illumina-
tion of showing the Leipsig, might be forced to do so
tolerably well by the assistance of monochromatic sun-
light. Admitting this, we still assert that such a glass
is unfit for the purposes of the working microscopist
beyond those it will respond to under the conditions
which we have presented. It further obtains that the
reader who, with such a glass, has followed us through
the Cherry field and the Monmouth, can proceed no far-
ther until we are ready to change the illumination.
Presuming, then, that the objective is quite competent,
and that the observer has thus far followed us in a sat-
isfactory manner, we attempt some further hints and
suggestions.

280 HOW TO SEE WITH THE MICROSCOPE.

Lesson Tenth. — Having succeeded in displaying the
striae of the Leipsig, selecting one of the larger and
most vigorous valves, it will be instructive to notice
once more, and particularly the edges of the shell, if
the frustule is flat and the objective equal to the work.
There ought not, as has been before intimated, be the
slightest indication of any line bounding the shell, such
as would be seen in a drawing on paper; but in place
thereof (so to speak) ; on looking closely, there may be
discovered, when things are just right, an exceedingly
fine band of peculiar light, the exact tint of which will
vary with the particular objective employed; and, as a
rule, the most brilliant tone will be noticed on the upper
half of the shell. If necessary, manipulate the mirror a
bit, and endeavor to "gather up" this band so as to
restrict it to the narrow space bounded by the very
edges and the termination of the striae. This band or

O

tint cannot be well seen on the Cherryfield or the Mon-
mouth, unless, indeed, on the very smallest shells, which
for the present have been held in reserve. Should there
be any tendency of the "lines" to "rise up," try a
deeper eye-piece, and, shifting the adjustment a trifle,
seek to remove the trouble, returning to the inch ocular
as quickly as practicable.

This pale boundary tint may, with different glasses,
assume quite different tints. With one it may appear
as a pale blue; another will show it of a delicate fawn
color, or even a pale pink. Objectives having the most
perfect corrections (I do not mean the most achromatic)
will give this band in what I call an " apple green,"

POSITION OF OBSERVER. 281

and the tone of the field will be the same as that of the
band. The student should practice until he shall be
competent to recognize the band and its accompanying
tint according to the particular glass employed. This
done, let him throw the glass a little out of adjustment,
and it will be seen that the band has disappeared, and
with it so has all the nice definition pertaining to the
edge of the diatom. Readjust the glass and watch for
its return as you manipulate. There will be no time
wasted at this.

A remark of a general nature is in place here. In
working over shells as coarse as the Cherry field or the
rhomboides, if the glass be well adjusted for one valve
it may be accepted that it is sufficiently so for all on the
mount. This is neither strictly nor practically true.
As some of the diatoms lie nearer the cover than others,
the adjustment requires to be changed in accordance
with the thickness of the intervening strata of -balsam ;
and on fine work, like the medium frustules of the
Leipsig, this point must be kept well in mind.

Now, with this point in mind, let the student, return-
ing to the Leipsig, adjusting his glass over the same
shell we have had in mind, getting things just right " to
a dot," let him slide the object carrier and hunt up an-
other and similar valve; that is to say, one that lays
just as flat in the balsam, and of the same size. Now
focus, and endeavor to say positively whether the new
shell is the same depth in the balsam as was the former.
If it shall be the same depth, that edge band will be
seen; otherwise not. Practice this we??, hunting from

282 HOW TO SEE WITH THE MICROSCOPE.

time to time all the larger frustules to be found on the
mount.

Before proceeding farther we have to say that the
foregoing ten lessons must be well studied and thor-
oughly understood. They have been arranged and pre-
sented so as to lead the student safely and progressively
through what has proved to many a labyrinth. We
have hinted at the difficulties which beset us and satu-
rate (so to speak) any attempt of ours to render our in-
structions perfectly intelligible to all. It follows, then,,
perforce, that defects and shortcomings in the way of
elucidation ought to be compensated for on the part of
the pupil by his vigorous determination to master the
situation. Again, in the exercise thus far given the in-
tention has been steadily held in mind ; first, to present
as plain a chart for the guidance of the learner as was
within our power; and, secondly, to keep well in hand
the necessary education of his eyes ; and in the latter
acquisition the element of time is quite as much a factor
as that of diligence and determination. We strongly
advise, then, the learner to confine himself to the sug-
gestions already given, until he shall feel himself thor-
oughly and practically familiar with them.

Lesson .Eleventh. — We will now study the Mon mouth
or the Cherryfieid (either will answer our purpose) once
more. Place the same on the stage, illuminate at an
angle of, say seventy degrees from axis. Bring one of
the largest shells to the centre of the field ; adjust the
glass and focus, getting the very nicest display of the
transverse striae obtainable. Now gradually let down

POSITION OF OBSERVER. 283

on the angle of the illumination little by little, adjust-
ing1 the mirror so as not to lose the show of the lines.

O

Now if the student has studied well what has thus far
been taught, he ought to be astounded at two conditions
which will flash on his intelligence. In the first place,
he will find that he can decrease the angle of the illumina-
tion down to, say 35°, all the while holding the stria?
well in hand. The probability is that he has now too
much light, and it will be well to try the effect of turn-
ing down the wick of the little lamp a little. Having
found the very lowest angle of the illumination that
will command a full show of the striae, return the mir-
ror just a trifle — just enough to reinforce the display of
the lines. Compare the effect with that of the previous
lessons. Notice that your striae shell and all have be-
come more transparent. There is not even a suspicion
of oblique illumination. Your diatom (and all the
others decently in focus in the field) swim in a sea of
fire. That's a cold word — "lightning" expresses the
idea better. Observe how flat the shell is! Not one
particle of distortion. Observe, too, that shadow we
have before called attention to, under the median line.
See how transparent it has become. Did you say that
you cannot see it at all? Yes, it's there ; look sharp
for it! Now look down between the striae. See how
nicely, how exquisitely they are cut apart. The spaces
between them are as visible as the striae themselves.
Notice, too, how that the most infinitesimal flickerings
of the lamp flame plays with consummate grace in and
among the lines. Look well to the edges of the valve.

284 HOW TO SEE WITH THE MICROSCOPE.

Watch, when the flame flickers, for that little band of
light, and when you catch it remark the wondrous deli-
cacy of its tone. Note, too, how the flickering of the
flame bathes the field with minute differences in tone,
things are almost alive. Compare what you now see
with anything that you saw a month ago. Has not your
time been well expended?

When the student has arrived at a position that will
enable him to fully appreciate what I am now writing,
he is safe. No matter should he have been accustomed
to the use of low apertures from childhood, he can never
be forced to return to his first love, nor will he have
trouble in following me to the very end.

Should the learner unfortunate!}7 find that in this les-
son he cannot see things as described, and presuming
that the objective is competent for the work, then it
must occur that there is either trouble with the manipu-
lations, or his eye is not sufficiently trained for the work
in hand. Hence he cannot get the mirror far enough
downwards; i. e., he is compelled, in order to see the
lines at all, to use light of too much obliquity. There
is but one remedy (if he is sure as to the capacity of his
objective, which he ought, perforce of the preceding
lesson to demonstrate), to wit: Practice until the end
shall be arrived at.

This effect, due to the lesser illumination, has, as the
reader will remember, received our attention on a fore-
going page. It may be advisable that he review what
has been said, and thus combine theory with practice.

Lesson Twelfth. — We are now to deal with the more

POSITION OF OBSERVES. 285

difficult class of objects, such as are recognized as the
severest tests. It will be much better for the student
if he confine himself to the instructions already given,
until he shall have become perfectly at home with his
objectives and mounts before paying attention to what
we shall here have to offer. In the remainder of the
lessons the education of the eye will be an indispensable
condition to success, and the instructions can only be
understood acceptably by those who have paid rigid
attention to the preceding instructions.

Arrange the stand with the inch ocular, lamp and
mirror, just as described in lesson first. Get out the
large bull's eye condenser and interpose the same be-
tween the lamp and mirror, the flat side towards the
lamp, and within a couple of inches from its chimney r
adjust the height of the condenser so as to throw the
light on to the mirror. The beam from the laimi may
be slightly inclined upwards, but never downwards. A
horizontal beam is not objectionable. Now experiment
a little. Try and get the lamp as closely to the left of
the stage as practicable, leaving room to work the con-
denser. Next, place the slide of Cherryfield or Mon-
mouth on the stage. NOW reflect for a moment. Where
is the point of maximum aperture of your objective?
And how will the cover of your mount respond to it?
If its point of maximum aperture be at nearly " closed,"
and your cover ot such a thickness as will allow the
glass to "correct" nearly at closed with glycerine, then
you are to use the same. If so be, however, that the
cover is thick enough thus to cause the glass to correct

286 HOW TO SEE WITH THE MICROSCOPE.

near closed with water as the intermedium, then, of
course, use water; or it may occur that the cover is an
exceedingly thin one — so thin that even with the glyce-
rine the correction would obtain at some considerable
distance from closed, in which case select another very
thin cover to supplement that on the mount. All this
has been discussed before, but in the preceding lessons
one might have got along tolerably well without par-
ticular observance of these conditions, but not so with
the problems we are now about to tackle.

Having then decided tho above point make the im-
mersion contact, and selecting a medium shell of the
rhomboides, bringing it to the center of the field focus.
Arrange the mirror so as to get the strongest illumina-
tion; let the lamp burn with a moderate flame; if now
there is obviously too much light, a perfect glare,
bring the lamp closer to you (keeping the flame edge-
wise to the mirror constantly) moving the same in a
line parallel to the left hand edge of the stage, readjust
the condenser and mirror thus lighting up the field
again. It will be seen that the farther the lamp shall
be thus moved the less will be the illumination. The
point to stop at is when you have shut out the super-
fluous sheen or glare. All this time we have supposed
that the flat face of the condenser was parallel to the
face of the mirror. Now change the position of the
condenser causing it to assume a slightly diagonal pose,
the nearer edge to be swung away from the stage;
when the condenser is exactly right the mirror will
have the appearance of being traversed by a line of

POSITION OF OBSERVER. 287

light, that is, it will not appear to be equally illumi-
nated as was the case before. Now look to the adjust-
ment of the objective, and by slight manipulations of
the mirror display the strke, which will be right
straight along work. Seize the base of the condenser,
stand firmly, supporting the left forearm on the edges
of the draw and table; move the condenser just a bit
to and from the edge of the table, noticing the effect
in the field, getting it thus in the best position possible.
Look to your mirror again and see if that " line" is
still there; this cannot be dispensed with. Now if
the directions shall be strictly carried out, the display
will be much finer than possibly could have been ob-
tained with the former illumination, the diatom will
seem to swim in a lake of fire, or as my pupils some-
times have said, " chain-lightning."

Do not be satisfied with any apparent success, but
repeat the method of illumination, time and time
again, comparing notes. The student will not prob-
ably meet with perfect success the first evening,
although it may be that he will be quite satisfied with
his efforts. If it so be that the condenser stands at
quite an angle, more so than you think ought to be the
case, never mind; if you have the right effects in the
field, you can study the rationale at your leisure. The
next thing in order is to study all the appearances
which have been pointed out in the preceding lessons.

Now shifting the object-carrier, hunt up a valve next
the very smallest on the mount, one that lies flat. If
you are using a one-tenth your inch ocular svill do, but

288 HOW TO SEE WITH THE MICROSCOPE.

if but a sixth, then you will need the " D" solid, the
one-half inch. Try now and display the strife on the
little shell ; remember that they are at best but very
thin and faint. Nevertheless, if there has been suffi-
cient practice with the " lesser illumination " previously
mentioned, there ought to be now but little trouble in
recognizing the lines. When once a good view has-
been obtained, the observer will be astonished by a
little experimenting, to find how far the lamp wick
can be turned down — just allowing the flame to peep
out of the cone — and still retain nice views of the
striae.

This entire position, including that of observer,
stand, mirror, and condenser, we have tried to illus-
trate in the cut on page 289, the diagonal pose of the
condenser we have intentionally exaggerated. It is
probable, too, that the student may find it necessary to
make some slight changes to suit the tools he may have
in hand. Let him keep this fact prominent, to wit,
although the condenser will give more light than the
illumination first recommended, nevertheless there
must be no more light used than is absolutely required
to see the object without difficulty as respects illumina-
tion. If it be desirable at any given time to employ a
higher ocular, always' turn up the wick of the lamp ; a
slight turn will be found quite sufficient, and while on
this subject let me say that nine out of ten microscop-
ists use far too much light. They seem to be impressed
with the idea that unless the object is bedazzled in a
flood of light that it is not well shown. All this is in

POSITION OF OBSERVER.

19 Microscopy

POSITION OF OBSERVER. 291

error; when such illumination is employed the chances
are that all fine 'detail of structure will be drowned
out, while the effect on the eyes is most injurious. Keep
then the field just as cool as shall be consistent with
vivacity and life, show your objects brilliantly, and see
that even the shadows are lively and transparent.
Grasp the mirror firmly; get in the habit of this;
when you touch it at all take hold of it boldly. There
is considerable for the student to learn in the proper
handling of the mirror, so as to combine boldness with
delicacy and efficiency. Now as you change its posi-
tion just a trifle, notice the action of the light. Does
it slide by as it were, without taking hold? Or is there
one particular position in which the light seems to
catch and " nip," bringing out the makings with a vim.
Now if the former is the case, there is something wrong
(the objective being in adjustment) and perchance the
whole system of illumination will require attention in
detail.

When the smallest shell of the Monmouth and
the Cherry field have been thus mastered (as to their
transverse striae) those of the Leipsig may be taken in
hand, and subsequently the smallest valves of the Isle
of Shoals; these are quite as severe tests as an ordi-
nary balsamed amphipleura pellucida. The slide of
Leipsig ought to be thoroughly mastered previous to
attacking the Isle of Shoals; all the peculiar appear-
ances which we have from time to time set forth, are
to be studied, and as the eyes become educated the
amount of obliquity of the illumination is to be de-

292 HOW TO SEE WITH THE MICROSCOPE.

creased. This latter item is to be a constant study ;
bear in mind this one broad rule, that to use a wide-
angled glass well is to work with the least obliquity
possible, and when over easy tests, with more central
illumination that can be effectively obtained with nar-
row a'pertured objectives. In short the employment of
the wide apertures points to the use of centrally dis-
posed light; this may be a novel doctrine to many, but
not at all new to the author.

Strive then to work with the most central illumina-
tion possible ; get rid of all shadows not indispensable ;
as a rule where the markings are dependent on thick-
ness of structure, the greater this difference of thick-
ness, i. e., the more prominent the markings, the less
will be the obliquity required; conversely the thinner
and the fainter the markings the more obliquity is
called for. Now the smallest shells of the Isle of
Shoals are extremely thin, the strise are not so very fine,
probably not measuring closer than 85 in .001 English
inch, but they are so thin and so fine as to beat out any
object-glasses, excepting those of the higher apertures.
And even with these the mirror will have to stand (ar-
tificial illumination being used as directed) at least 60°
to 65° from axis; a fine one-tenth ought to show any
and all of them, either with the one inch or one-fourth
inch ocular. A similar one-sixth will require the half-
inch.

Now, in the study of the last four or five lessons, the
student is to constantly endeavor to improve himself in
the adjustment of his objective. The broad land-marks

POSITION OF OBSERVER. 293

have been laid down for his guidance, and these should
not be lost sight of. As his eyes become trained to this
kind of work, he will begin to pick up items of value
on his own account. Especially will he arrive nearer a
due appreciation of what we mean by tone of objective
and field. He will thus be able to recognize for him-
self, confidently, too, when things are just right. Ditto,
when they are not just right. Should the collar of his
objective need to be changed, he must be able to make
such change at once, and in the right direction. There
must be no indecision — 110 guess work. He will have
learned, also, that when the adjustment is exactly cor-
rect, not only has the display of the striae become more
satisfactory, but that the general appearances of the
entire shells have improved. This effort at improve-
ment of the adjustment of the objective should become
a constant and never ending study ; in truth, after one
becomes tolerably advanced therein, it is no longer a
" study," but rather a pastime.

We desire to insist with all the vigor we can com-
mand, that there is force attached to the reciprocal re-
lations above named, to wit: That when the student,
perforce of intelligent practice, shall be in position to
assert, dogmatically, that his manipulations are correct,
he will, conversely, be just as competent to reaffirm the
fact when things are not in proper adjustment. When
this obtains to an acceptable extent, he will be compe-
tent to use his glass for any field of investigation that
he may elect, and, as a matter of course, he will regard
those whom he is assured have not given proper atten-

294 HOW TO SEE WITH THE MICROSCOPE.

tion to this essential item, knowing, too, that it is es-
sential— " cum grano satis." With our private pupils
we have often tried amusing- experiments, simply to
become assured of their proficiency in this matter, thus :
We sometimes place a drop of mucilao-e on the interior
surface of the field lens of the eye-piece, replacing the
same and watch for results. If the pupil is well trained
there is no deceiving him. He will assert roundly that
something is the matter. If I say to him, mildly, " why,
that's pretty well, isn't it?" He replies at once, in tones
that there is no dodging, "No, sir; there is something
wrong, sure." And then, again, I have had the pupil
pay me back in my own coin — placing a similar drop of
mucilage in the interior surface of my own oculars.

We have already said that no two lenses work ex-
actly alike. It remains, therefore, for the pupil to make
a specialty of his own object glasses, first assuring him-
self, preferably by the advice ot some expert friend, that
he shall not waste time over an inferior glass. While
he thus becomes more and more familiar with his own
objectives, he will also acquire a general knowledge of
all, and will in due time be able to take a strange object
glass and work it nearly or quite up to its maximum.

Unless the observer be provided with a really super-
fine objective, he can hardly make much headway in
the examination of the smaller shells of the Saxonica
from the Isle of Shoals.^ Should he have much trouble
in getting the striae on the very largest frustules, these
appearing quite obscure and of a generally uninviting
aspect, the edges badly defined, and more or less distor-

POSITION OF OBSERVER. 295

tion prevailing, he may be pretty sure that his glass is
at fault. His time will therefore be much better spent
in the examination of such objects as come within its
powers. This point is well worth close attention, thus,
perhaps, saving a double outlay of time and patience;
and there has been a vast amount of valuable time
wasted in fruitless attempts to resolve severe tests,
for which purpose the objective was totally unfit and
incapable.

The illumination we have just described is quite suffi-
cient for the display of the transverse striae of either
slide of Amphipleura. As we have before stated, the
"Bridge of Allan" is the easier of the two and should
be studied first, and the student should give preference
to the cleanest shells on the mount. If the smaller
scales of the Isle of Shoals are well seen, and the
" Bridge of Allan " resist, the fault will certainly be in
the adjustment of the objective over the latter mount;
possibly it may occur that the observer has selected an
exceptionally difficult shell of the Pellucida. The bet-
ter way will be to look over the slide in detail, of course,
as before advised, giving preference to the cleaner and
most inviting frustule.

If so be that the student has the Moller probbe plate,
the illumination given is also quite sufficient to display
the Nos. 18, 19, and 20. After he shall have become
well advanced, there are some particular advantages
connected with the study of this plate. He ought to
see the Nos. 18 and 19 with but little trouble, and in a
little time with the radial arm at 45° from axis. On this

296 HOW TO SEE WITH THE MICROSCOPE.

plate passing from No. 19 to 20 is quite a jump. One
may see the No. 19 in a very satisfactory manner, and
yet fail of the No. 20. At the onset it will be better
to secure all the obliquity of light possible. Should
the Acme or the little Histological stand be used, the
upper one-third of the mirror may rise above the stage,
the lamp and condenser to be adjusted with the greatest
nicety. If the No. 20 resist the attack, it is preferable
not to spend much time over it, but go at once back to
the No. 19 and endeavor, by some careful re-adjustment,
to get a still better view of this ; and when satisfied that
such has been accomplished then return to the attack
on the No. 20. One will always succeed much faster by
trying to improve what is seen than by blindly working
over an object of which the desired details cannot be
displayed at all. The ease with which the learner can
run from one test to another renders the Moller plate
very acceptable to the learner. Should it occur that
the No. 20 make a protracted resistance, let the above
programme be adhered to, spending nearly all of the
time in perfecting the display of the» No. 19. It may
be worth while to add that the Moller Amphipleuras are
about on a par, in point of difficulty, with those from
Aberdeen, Scotland. If there be any difference, my
impression is that of the two the Moller No. 20 are
perhaps the easier test.

In studying the Aberdeen, or in fact any mount con-
taining severe tests, it is always advisable to correct the
glass approximately by selecting some fine object, of
which the details can be displayed by such approximate

POSITION OF OBSERVER. 297

adjustment. For instance, on the "Aberdeen" it is
probable that ome specimens of Mtzschia may be found.
by hunting for them, and this should be done at once,
and the glass corrected as nearly as possible. An ap-
proximate adjustment will suffice to reveal the trans-
verse striae, and the initial display ultimately improved
by force of a little well directed manipulation. It
may occur, too, that some of the nitzschia are more
difficult than others. This being the case, the stu-
dent is to master these successively before attacking
the amphipleuras.

In the practice of all the preceding lessons, and over
the test slides, it will be essential that the pupil, after
having adjusted his glass as perfectly as may be, note
the exact division of the collar graduations. This he
should make a memorandum of, so that he can be able,
if necessary, to readjust the objective to the mount
without loss of time. But this is not all. He will
find that as he acquires proficiency by practice, that he
will, time after time, change these recorded numbers,
and will be inclined, perhaps, to smile at the wildness
attending his initial attempts ; and by thus comparing
the present with the past, he may be encouraged as to
the future. This habit of noting in black and white
the best attained adjustment of the objective from day
to day should be rigidly persisted in for at least a
twelve-month.

298 HOW TO SEE WITH THE MICROSCOPE.

WORK OVER DRY MOUNTS WITH HIGH APERTURES OBJECT-
IVES.

After, and not before, the student has become profi-
cient in the preceding lessons, it will be advantageous
for him to procure dry mounts of the acknowledged
diatom tests, and study well their peculiar action under
the objective. At a glance it will be noticed that the
dry frustules are much more vigorous than those mounted
in balsam. They have more body, appear more solid,,
the image is stronger every way. Hence it is that an
objective may shew a dry mount tolerably well, and yet
be utterly defeated by the same valves when balsam
mounted. Should the student be well versed in our pre-
vious instructions, he will find little difficulty in dealing
with dry mounts. As a rule, the Litter are to be illu-
minated with pencils of less obliquity than objects
mounted in balsam. In the dry mount, too, we have
greater contrasts of light and shade. These differences
will be at once noticed by the intelligent pupil, who
will find little difficulty in adapting himself to the situ-
ation. He should keep in remembrance this one fact,,
to wit: That, owing to the superior brilliancy pert-lin-
ing to the dry mount, little differences in the collar ad-
justment are not so perceptible as is the case with bal-
samed objects; nevertheless, the difference is there, and
well worth the study necessary to recognize these little
differences. Again, should the learner desire to com-
pare one objective with another as to their comparative

WORK OVER DRY MOUNTS, ETC. 299

defining powers, always choose a balsam mount, and the
thinner and weaker the shells (within reasonable limits)
the better and the more palpable will be the comparisons.

We advise every lover of a good objective to provide
himself with a slide of the genuine English podura, as
a matter of course dry mounted, and let him be careful
to keep it dry! Amount that has once, only, been
swamped in water will be probably badly damaged ; and
should it occur that water leaks through the cement, it
should be immediately dried by moderate artificial heat,
and subsequently laid away in a warm place for several
hours. Too much care cannot be taken with a really
valuable slide of podura. Prof. Phin says, in his excel-
lent work, " How to Use the Microscope," alluding to
the podura scale, " page after page has been written for
the purpose of showing how the podura ought to look*
and still the question seems to be undecided."

A year or two ago a lively discussion sprang up in the
London Monthly Journal ofMiwoscopy, between Messrs.
Piggott and Wenham, the former contending that the
true resolution of the podura resulted in dots. Mr.
Wenham, on the contrary, warmly taking sides with
Ross and Beck, holding that the "exclamation points''
were the proper thing to be shown. A month or two
later a most curious article appeared in the " Popular
Science Monthly" contributed by Mr. John Michel Is, and
entitled " The Microscope and its Jfeinterpretations."
The point of Mr. Michell's article was to show the want
of reliability attending observations made with the mi-
croscope. To make this point salient, he referred to the

300 HOW TO SEE WITH THE MICROSCOPE.

London controversy of the Messrs. Piggott and Wen-
ham on the podura question, and also gave the state-
ments of other English observers. Among the illustra-
tions accompanying this article were five or six cute
showing the same scale of Podura as seen in the micro-

O

scope under different illuminations. Thus one identical
scale was exhibited to the reader as widely changed in
its aspects as could have occurred had dissimilar scales
been selected for the comparison. One or two of the
results shown were evidently owing to distortion occur-
ring from the use of a badly corrected objective.

Now let it be remembered that Mr. Michells, in thus
stating his authority for the wwkhiterpretations of the
microscope, worked with legitimate material, and the
work over the podura presented was such as had been
arrived at by English microscopists of acknowledged
competency. There must be something wrong ; in what
direction shall we look for the cause thereof?

So far as the exhibition of " the markings " of the
podura are concerned, they are an easy test ; i. e.< almost
any common-place glass will show them after a fashion,
while what would be known as a " real honest working
sixth or eighth " will show these markings with consid-
erable force; and such a display would likely be as
acceptable to the novice (or to those who had never
worked with better objectives), as the view given by a
superb high balsam angled glass by Spencer or Tolles.
But mark this: Hardly two of the " real honest work-
ing glasses," owing to the hap-hazard character of their
corrections, will give the same appearances, while the

WORK OVER DRY MOUNTS, ETC. 301

objectives of Spencer and Tolles will have but one and
the same constant story to tell. With these, properly
manipulated, it is impossible to get aught over the po-
dura but the exclamation points: With these superb
glasses such a thing as the reproduction of the several
appearances shown by one and the same scale, as ex-
hibited in the cuts by Mr. Michells, becomes an impos-
sibility. And here, in the opinion of the author, may
be found the key of the problem, to wit: The better
glasses showed the podura tolerably well. The poorer
ones, those " real honest working glasses/* of which we
have heard so much about, were bound to set forth their
individual ^'^representations, and thus furnish material
for contributions to periodical literature like that of Mr.
Michells.

As to the true structure of podura. there can be
little doubt; there has never been but one opinion
among American observers accustomed to the use of
the finest American objectives, and the spines or ex-
clamation marks are accepted as the true resolution of
these scales. By the aid of electricity, these spines
have been detached from the body of the scale; the
detached spine together with the parent scale were
photographed and thus presented to the readers of the
"Lens."

We have already had occasion to say that Mr. Geo.
W. Morehouse, of Waylancl, New York, was the first
observer who demonstrated the capabilities of the
Beck vertical illuminator; when used in conjunction
with American object-glasses of high balsam angles,

302 HOW TO SEE WITH THE MICROSCOPE.

Mr. Morehouse's results in displaying- objects by re-
flected light under the higher powers of the microscope
were truly astounding, and his paper read before the
Dunkirk Microscopical Society of Dunkirk, arrested
the attention of the author, who immediately repeated
Mr. Morehouse's observations with the liveliest satis-
faction. Mr. Morehouse particularly called attention
to the unrivalled views thus given of the podura,
adding that they seemed to settle all question as to the
nature of these markings. Mr. Morehouse observed
also that near the ends of scales the spines were some-
times to be seen projecting beyond the scale itself, and
the author can affirm the same from his experience.
As suggested by Mr. Morehouse the vertical illumina-
tor, from the nature of its action — dealing entirely
with surfaces only — not only deprives Mr. Mitchell's
paper of argumentative force, but fairly turns his
weapons against him, pointing to the podura, indeed,
as a very proper object with which to demonstrate the
reliability of microscope observations.

The student will find the study of the podura a valu-
able assistance in teaching him the behavior of fine
object-glasses over dry mounts, and when he shall by
dint of long practice become sufficiently expert to de-
tect and appreciate the beauty of the display as given
by balsam aperture objectives as contrasted with the
work of medium angled glasses, he will suffer no re-
grets as to the time and patience this accomplishment
may have cost him.

We have insisted on the use of the genuine English

WORK OVER DRY MOUNTS, ETC,

303

podura, and as we have stated, this slide must necessa-
rily be selected by some friend competent to the task.
The American podura is quite inferior to the English,
yet of the two a slide of the very best American
should be accepted rather than a notably poor English
specimen. The former will be much better than none
at all, but let it be remembered that the English are
the desired thing. Now as to the proper appearance of
these scales under the objective, we must state that it
is perfectly impossible to give any truthful representa-
tion on paper. The following cut
taken from Prof. Phin's book,
copied irom the illustrated cata-
logue of the late Richard Beck,
may help matters some, and shows
the podura with tolerable precision,
when the same is seen with a dry
one-eighth, say of 130° aperture
magnified 1,300 diameters, and illuminated with light
as central as possible. Now let the student take a half
sheet of writing paper and roll this up so as to form a
tube, and examine the cut attentively, looking through
this tube, as is frequently done when examining draw-
ings, etc. Letting a strong light fall from the direc-
tion indicated by the shadowed sides of the markings,
we think that most of our readers will have no diffi-
culty in noticing that the " exclamation points " seem
to " rise up " above (apparently) the general surface of
the scale. Our principal design in calling attention to
this feature is that he may thus recognize an effect to

304

HOW TO SEE WITH THE MICROSCOPE.

which we have had occasion to allude to in previous
pages, when treating of certain diatom tests. Now
this same effect is easily seen in the podura when under
the objective, and we have never been entirely able to
get rid of it, especially when a glass of moderate angle
is employed. Now the reader knows from personal
experience ]ust as much of this borrowed cut as does

the author. We will,
however, hazard the
assertion that the il-
lumination shown was
about 20° from axis,
the glass having aper-
ture as above stated,
of perhaps 120° or 130°.
Let us imagine then
that we thus have such
a display under th6 mi-
croscope; and again,
that we remove the
objective and replace
with another of high

balsam angle. In tire cut on this page we have endeav-
ored to depict the changes.

First it will be seen that with the radial bar in pre-
cisely the same position we have the effect of greater
obliquity; the shading is more decided and (over the
tube) the lights are more intense and brilliant. Now
examine this cut with the paper tube ; it will be ob-
served that the exclamation points do not " rise " so

WORK OVER DRY MOUNTS, ETC. 305

much as was the former case. They indeed appear in
good relief, but they do not seem to float clear from
the body of the scale; these appearances are to be
watched under the microscope, and the obliquity of the
illumination diminished to the least angle without
allowing the spines to rise. When the adjusting collar
and the illumination are just in the correct position,
the small end of the " wedges " or " exclamation points
are to be sharply defined. These scales may be exam-
ined either in a vertical or horizontal position ; as a
general thing the vertical will be the preferable posi-
tion. Most mounts of podura will contain scores of
scales, while for the most part there will be less than a
half-dozen good ones. The student should look care-
fully to this, and make the best selection possible. Ke-
ferring to the use of the vertical illuminator, Mr.
Morehouse called my attention to a curious fact con-
nected with the study of these scales, namely, that the
smallest and most uninviting of these, as shown by
transmitted light, seemed under the vertical illumina-
tor quite as strong, vigorous, and satisfactory as any.
We found Mr. Morehouse's observation true as respect
to many other insect scales we had occasion to examine.

The following, mounted dry, will form useful objects
and may be advantageously studied conjointly with the
podura :

Scales of Lepisma saccharina — Degeeria — Macrotoma
major — Petrobius maritimus — Pontia brassica — Morpho-
menelaus — Tinea vestimenti — Gnat — Hipparchia Janira
— Wing of Gnat — any of the scales from the lepidop-

20 Microscopy.

306 HOW TO SEE WITH THE MICROSCOPE.

tera will answer a good purpose, and in the summer
time the student will find a plenty of these visitors,
and from such material many excellent mounts can be
prepared with little loss of time and at a slight ex-
pense. We recommend that the pupil become well
accustomed to handling insect scales before attempting
the miscellaneous examination of anything and every-
thing mounted dry that perchance may be directly at
baud. After considerable proficiency has been secured,
the student may test his powers thus : Let him pro-
vide himself with a dry mounted trachea, say of a bee;
use the lowest ocular, select the strongest and most
vigorous part of the object where the coils are the
largest and the strongest, and adjust the glass as nicely
as possible thereon. This done, choose one of the
longest continuous coils and see how far this can be
followed towards the smaller end. Now having arrived
at the limit, so that the coils can but just be perceived,
manipulate the adjustment; now if you succeed in get-
ting very much better definition, the proof is before
you that you were in error at the commencement.
Make a note of the situation, and throwing the glass
intentionally out of adjustment again, repeat the ex-
periment until you shall be enabled to certainly make
the initial correction with tolerable certainty and accu-
racy. This is first-class practice, and will be of the
utmost value in general work over dry mounts. The
trachea, too, is a real good test object. The author has
worked ten hours at a sitting endeavoring to trace
these coils to the very last end, but has thus far met
with defeat.

WORK OVER DRY MOUNTS, ETC. 307

As to the general examination of the various dry
mounts, or of histological preparations mounted in
glycerine, nothing but the most general directions can
be given. The previous study of the diatoms will
become a valuable assistance to the student, and this
study should be still kept up in the examination of dry
mounts especially. Of such objects as have palpable
size, and can be seen with the naked eye, as is the case
with very many histological mountings, the pupil must
expect more or less annoyance from the interference of
the various shadows, from different parts of the struc-
ture, situated in different planes. If, in such a mount
it be desired to examine critically minute details, make
it a point to select a bit of the object that has per-
chance been accidentally removed from the main body,
and when you prepare your own mounts keep this
point in mind. A good general rule with such mounts
is to keep the illumination as nearly central as possible.
In the adjustment of the objective the same plan is to
be adopted, selecting when available the smallest
isolated fragment, with the illumination within 35°
to 40° from axis (or less) the low angled sub-stage
condenser will be valuable. It however requires some
study, as we have found by practical experience, to
work the condenser so as to secure its best effects. It
is a matter, also, that calls for the outlay of time and
no little patience. Nevertheless, the reward will repay
the effort.

Through the kindness of Mr. Zentmayer, who con-
structed the apparatus we have been experimenting

308 HOW TO SEE WITH THE MICROSCOPE .

with condensers of very small diameter, several of
these of varying focal lengths were fitted to the same
mounting. Either glass could thus be used at pleasure.
The mounting was conical and the base being also of
small diameter, say about one-fifth of an inch, our idea
was by this arrangement to keep the angle of the con-
densing lens as low as possible, and by the peculiar
form of its mounting to illuminate as little as possible
of the object and with an extremely acute cone of light
and at the same time, allowing sufficient lateral range
that the instrument might be placed in as oblique posi-
tion as possible. The idea seemed theoretically sound,
and we have spent much time in the experiments hoping
to give our readers something of value, but we were
doomed to disappointment. (Not the first experiment
of ours which has failed). The instrument is very
troublesome to use, requiring often some little time to
coax the light through the little cone, and when once
obtained, the slightest movement of the mirror will
destroy what has been done. Nor when doing its best
were the results any. better than those obtained by the
Gundlach, or Beck cheap inch which has already beeii
recommended for general condensing purposes. We
still believe that some improvement will be made in the
direction of our experiment, and hope that other ob-
servers will make similar efforts until further success
shall be secured.

OIL IMMERSION OBJECT-GLASSES. 309

OIL IMMERSION OBJECT-GLASSES.

Since the introduction of the duplex objectives
another form of four-system, wide apertnred glass,
constructed by Carl Zeiss, of Jena, Denmark, has made
its appearance in this country.

With the advent of these glasses came also the an-
nouncement that their balsam apertures excelled those
of the American duplex. A novel feature in the
mounting of the oil immersions was that they were not
provided with adjustment collar; it being asserted that
the only requirements necessary to secure the perfect
action of the object-glass were to use the same with a
tube of exactly ten inches length, and to employ cedar
oil as the immersion medium.

It was further stated that when these simple require-
ments were alone attended to, that no further adjust-
ment of the objective would be required, and that the
performance ot the object-glass would be found un-
equaled.

As might be supposed, the above claims on behalf of
the oil immersions were destined to receive attention
at the hands of American microscopists.

A fact well known to experts concerning wide aper-
tured objectives is this, viz: An object-glass exactly
corrected to the eye of A may not be in exact correc-
tion to the eye of B without suitable change of the
collar adjustment.

During a sitting with Mr. Chas. A. Spencer at
Buffalo last fall, the above fact became immediately

310 HOW TO SEE WITH THE MICROSCOPE.

apparent. Mr. Spencer's adjustment of his duplex
one-tenth objective (which we were then using) being
invariably three divisions of the collar graduations
nearer "closed " than my own.

It is obvious therefore that an " oil immersion " suit-
ably corrected to the vision of Mr. Zeiss when worked
with ten-inch tube, might require a special correction
when in the hands of Mr. Spencer, or myself. Feeling
therefore assured of the error embodied in the popular
representations concerning the oil immersions of Mr.
Zeiss, the author solicited and obtained one of Mr.
Zeiss' circulars, which, being official, will, it is believed,
be read with interest. With the exception that a few
typographical errors have been corrected, the following
is otherwise a verbatim copy.

NEW OIL IMMERSION OBJECTIVES. ONE-EIGHTH INCH.
ONE-FIFTH INCH.

"This object-glass is adapted to an immersion fluid,
which in refraction and dispersion is equal as nearly as
possible to the crcwn glass, a plan proposed by Mr. J.
W. Stephenson, of London, as a devise for increasing
the aperture and for dispensing with correction.

" The lens constructed on this plan — a four-fold sys-
tem of pp. one-eighth focal length, calculated by Prof.
Abbe — shows an aperture of unusual amount, combin-
ing a most perfect definition with a reasonable working
distance. It works equally well through thick, thin,
and thick covering glass without needing special cor-
rection, owing to the identic refraction of the immer-
sion-fluid and the covering-glass.

NEW OIL IMMERSION OBJECTIVES, ETC. 311

" The numerical aperture of the object-glass (accord-
ing to Prof. Abbe's definition, the product of the sine
of angular semi aperture with the refractive index of
the medium exposed in front) is brought to the num-
ber 1.25 exactly, which corresponds to a balsam angle
of 113° and is in the ratio of 5:4 greater than would
be the maximum aperture, 180° in air, of a dry lens,
considered in its numerical equivalent, the resolving
power correspondingly affords a visible increase com-
pared with immersion-lenses of the common system,
which generally do not exceed 1.10 in the numerical
equivalent of aperture.

" As to the immersion-fluid a large number of ex-
periences has shown the oil of cedarwood (ol. ligni
cedri) to be the most fitted, though it is in a slight
degree still less refractive than ordinary crown-glass ;
other liquids of higher refraction exceeding too much
in dispersive power. This oil (of which a sample will
be sent with the objective) may be got anywhere in
sufficient purity.

" For controlling its qualities or those of other
liquids, which perhaps might appear convenient, a
special test-bottle is forwarded with parallel plane faces
and a prism of crown-glass, cemented to the stop of
this bottle. The vertical spar of a window seen
. through the prism and through the oil beneath, should
appear without a sensible defection and should show
bodies only slightly colored, if the liquid has the right
quality.

" The pure oil, ligni cedri, will afford the best color

312 HOW TO SEE WITH THE MICROSCOPE.

correction for oblique light ; for observation with cen-
tral light the image may be obtained still more colorless
if a suitable quantity of a higher dispersive oil (oil of
fennel seeds or anise oil) be mixed with that of cedar-
wood. But in this case the refraction of the mixture
should be reduced to the original refraction of the oil
of cedar-wood by adding some pure olive oil ; the test-
bottle being always applied for regulating the mixture.

" A few other oils: The oil of copaiva-balsam and
the oil of sandal-wood approach so close to the oil of
cedar-wood in refraction and dispersion, that they may
Be used for it, instead of it, if they should be prefer-
able in any respect, provided the test-bottle has stated
the right quality of the sample.

" The use of these oils will not be injurious to prepa-
rations which are hermetically closed, as it is likewise
necessary for water-immersion, although the black var-
nish on some slides (not on all) will be slightly dis-
solved by a prolonged exposure to the oil, its action
will not be offensive within a moderate time; and in
most cases any contact of the fluid with the edge of the
covering-glass may be avoided, by the oil not being
applied in a greater quantity than is necessary. A
minimum drop on the covering-glass, and such a one
on the front lens being quite sufficient for observation;
besides that, the varnish of the slides may be perfectly
secured against the oil by a solution of shellac in
alcohol.

" A special advantage will result from this mode of
immersion for the more difficult dominions of petro-

NEW OIL IMMERSION OBJECTIVES, ETC. 313

graphic work; since rock-slices for inspection with the
microscope will become perfectly transparent, using
the oil without needing a polished surface or a cover-
ing-glass cemented on, and may be observed to a
greater depth than would be accessible to the higher
powers of the ordinary system.

" In every case the new object-glass, not considering
the greater optical capacity in bringing out difficult
structures, will prove exceedingly convenient for use,
from dispensing with any trouble in finding the right
•correction.

"Of course the full performance of the increased
aperture can be effective only on preparations which
are mounted in balsam (or any other medium exceed-
ing 1.25 in the refractive index) or which, if mounted
dry, perfectly adhere to the coveriny-glass . On objects
separated by air from the covering-glass the lens will
not work better than any good immersion-objective
with an aperture equivalent to an air-angle of 180°.

44 Besides this, for displaying the full performance in
oblique light, the illuminating-apparatus must yield
pencils of greater obliquity than are directly accessible
to a slide from air. The most simple devise forgetting
light on such an obliquity without needing a special
apparatus (immersion condenser) is a plano-convex
lens cemented to the under surface of the slide by a
minimum quantity of oil. The ordinary mirror of the
microscope brought to a moderate distance from the
axis will now yield pencils of any wanted obliquity ; a
lens fit for this use will be added to the object-glass.

314 HOW TO SEE WITH THE MICROSCOPE.

" If ordered for English microscopes the lens will be-
perfectly corrected for a tube of ten inches exactly, and
no sensible deviation from this length would be admis-
sable without a loss of perfect definition. However,,
owing to the slight defect of refractive power in the
oil of cedar-wood, some advantage may be found by
lengthening the tube for one-half to one inch while ob-
serving through extremely thin covers (less than 0.004
inch), and by shortening it for one-half to one inch in
the case of very thick covers (exceeding 0.008 inch).*

" The object-glass is made with fixed brass work and
with standard screw (like all my object-glasses) ; the
price of it is 240 marks ; the price of the one-twelfth
is 320 marks; the aperture guaranteed to be not less
than it is stated above. The lenses are screwed together
with moderate pressure and may be unscrewed without
great effort, but I caution expressly against unscrew-
ing them ; owing to the great aperture the system is
extremely sensible to the slightest defect of centering
the smallest particle of dust, or -the least moisture get-
ting into the screws, and the unavoidable difference of
pressure when screwing the lenses together, would
cause a sensible loss in the performance of the glass."

JENA, March, 1878. (Signed) CARL ZEISS.

One can hardly read the foregoing somewhat contra-
dictory document without arriving at the conviction
that Mr. Zeiss has suffered severely at the hand of his-
translator. Be this as it may it will be noticed that he
asserts that the oil-immersions practically NEED adjust-

* Italics mine, J. E. S.

NEW OIL IMMERSION OBJECTIVES, ETC. 315

meiit, which adjustment he recommends be accom-
plished by manipulating the draw-tube to a possible
extent of two inches when working over covers varying
from 0.004 to 0.008; and here let the reader be re-
minded that these figures do not by any means express
the maximum variations of cover-glasses.

o

I have had an opportunity of critically examining but
one of these objectives, a one-eighth, imported by a
friend. This glass when worked with ten-inch tube
over my usual covering-glasses required downright
engineering of the draw-tube; furthermore, when
worked over covers 0.008 inch thick, it was impossible
to correct the glass at all, as the draw-tube of my
stand when fully closed would not decrease the distance
sufficiently to secure the proper correction of the ob-
jective.

The performance of this one-eighth (when exactly
corrected) was very fine indeed, and closely resembling
the work of the Tolles or Spencer duplex. Superb as
its definition was, it did not excel that of my Spencer
duplex one-fourth — a glass of half its nominal power.
The balsam aperture of the one-eighth was about the
same as that of my duplex glasses.

During my first evenings with the oil immersion the
cedar oil behaved very well, but on the second and
third sittings it made me trouble enough. With the
tube inclined (as usual) the oil would most unaccount-
ably take a notion to run away; when this occurred,
any attempt to reinforce by adding more of the oil,
made things worse ; the only remedy was to clean the
slide nicely and commence operations again, de novo.

316 HOW TO SEE WITH THE MICROSCOPE.

The author learns from good authority that Mr.
Zeiss has recently extended the balsam aperture of his
oil-immersions improving thereby the performance.

Oil-immersions are now made by Mr. Tolles and Mr.
Spencer. These makers, however, supply the collar
adjustment (as should have been done by Mr. Zeiss).
Mr. Spencer's objectives we are informed are arranged
so as to work with oil or glycerine contact.

While in the oil business as above stated, it occurred
to me to try the effect of various oils with my duplex
glasses. After a little experimenting, I found that
ordinary kerosene, well washed in alcohol, worked
most beautifully with both the Tolles one-tenth and
the Spencer duplex one-fourth, with either glass when
thus immersed I got the most exquisite displays of the
most difficult known tests. It thus came to the surface
that I had harbored oil immersions while ignorant of
the fact.

That the cedar oil diminishes the range required in
process of adjusting for varying thickness of cover
must be granted, hence the novice using the Zeiss im-
mersions being necessarily restricted to this more lim-
ited range might possibly get better initial perform-
ance than would result in his first attempts to manipu-
late a Tolles or Spencer four-system objective.

In dispensing with the cover adjustment and its
accompanying mechanism (such as furnished by Spencer
or Tolles), falling back on the clumsy draw-tube as a
substitute, the cost of construction is materially re-
duced. Those affected with the res angusta domi might

NEW OIL IMMERSION OBJECTIVES, ETC. 317

doubtless contract with either Tolles or Spencer for
objectives on the model of the Zeiss, and fully equal to
the latter in performance, and at figures considerably
below those quoted in the Danish catalogue.

Our experience with the Zeiss oil immersions has
neither weakened our appreciation of the screw-collar
adjustment, nor our high estimation of wide apertured
objectives of American manufacture.

CHAPTER VIII.

A WORD OR TWO ON VOLUMETRIC ANALYSIS.

The value of the microscope to the medical profes-
sion is greatly enhanced by the conjoint use of a little
chemistry; in the examination of urinary deposits it
will often occur that neither the microscopical nor the
chemical analysis per se would be complete or entirely
satisfactory, while the combined results of these might
lead directly to the information desired.

Micro-chemical examinations of urines are of the
utmost importance to the practitioner ; among the best
English works on the subject may be named those of Gold-
ing Bird, Beale, Roberts and Harley. The beginner will
derive much satisfaction from the work of Dr. Bird,
which although written twenty years ago is essentially
good at this day. The reader should keep in mind in
the perusal of either of the above authors, that micro-
scopy has of late years suffered material advancement,
hence it is with the superior objectives now at our com-
mand, we are able to cross-question some of the plates
contained in the above-named books.

Almost anyone looking over the representations of
44 tube-casts" as pictured by Dr. Beale, would natu-
rally arrive at the conclusion that there could be no
doubt as to the recognition of these objects in practice.
It becomes my duty to say, therefore, that in neither
of the works referred to, can be found a reliable repre-

318

ON VOLUMETRIC ANALYSIS. 319

scntation of a genuine ' « tube-cast " ; while on the other
hund the learner depending entirely on the information
•conveyed to the eye by the plates is surely liable to be
misled. It is very far from our purpose to make any
attack on the English authorities mentioned; from
-either of them we have derived a great deal of useful
.and valuable information, and they are to-day works,
to which we make frequent reference. And then again
we doubt seriously, if an accurate idea of a " pale
hyaline cast " can be conveyed by means of drawings.
The learner, however, may rely on the text of our
favorite authors, and at the same time use due care
that not every adventitious filament, hair, etc., be ac-
cepted as a genuine " tube-cast."

To detect with certainty a genuine " cast," one of
the feebler order requires just as much care and study
.as would be required to show the lines on the Nos. 18
or 19 of the Moller test plate, and requires also just as
good instrumentation.

Having thus alluded to one serious source of error,
we have to say that it is no part of our purpose here to
write a treatise on urinary deposits, although we hope
to accomplish something in this line at no distant day
our present purpose is to give the medic a hint or two
as to the little apparatus required in the volumetric
analysis of urines, and to instruct him in the prepara-
tion of the necessary chemical solutions employed in
such analysis; $15.00 or even less will purchase a tol-
erably effective outfit.

320 HOW TO SEE WITH THE MICROSCOPE.

APPARATUS.

Six test tubes ; let four of these be large size. Spirit
lamp. Four or five two-ounce beakers. Bink's 250
grains burette. Two or three small glass funnels, say
ot two-ounce capacity. Filters to match the above.
Two or three glass rods. Two or three brushes for
cleaning test tubes ; ditto, for burette. Litmus paper,
blue and red. Two measuring pipettes, one-half, one
and two fluid ounces. Urinometers.

All of the above can be obtained of Messrs. Gr. Tie-
man & Co., 67 Chatham street, New York, and will
cost less than $7.00

Additional to this list we recommend the purchase of
three or four "Marais" graduated tubes for approxi-
mative analysis. These cost $1.50 each. At least one
of these should be provided.

A delicate balance, one turning with one-fourth grain
when loaded with an ounce in each pan, will be required.
Most of the books treating on volumetric analysis de-
mand that the balance should be quite an expensive one.
Nevertheless, the simple little models which can be pro-
cured almost anywhere, and costing less than $3.00, can
be made to answer tolerably well. Those to whom the
expense is not objectionable will find a really fine bal-
ance enclosed in a glass case a luxury. Ours, made by
Troemner, of Philadelphia, turning with, say one-fiftieth
of a grain, costing $40.00, has given excellent satisfac-
tion. Reliable instruments, by Becker, can be obtained
in the cities, at prices from $10,00 upwards. Those who

APPARATUS. 321

have used them speak highly of them ; but for the pur-
poses of the practitioner, such instruments are not
strictly a necessity. The small German scales found in
the office of almost any physician can be made, with a
little attention, to do very fair work. If such be se-
lected, it will be of the very first importance to possess
a reliable set of weights ; those furnished with the cheap
instruments are not to be tolerated. Nor is it safe to
appeal to the nearest druggist. The safest method is
to make one's own, which is accomplished with no great
outlay of time or money.

First, purchase a set of Troemner's "aluminum"
grain weights, costing fifty cents. These consist of a five,
four, two three's, two, one, and one-half grain weights.
With these in hand it will be easy to construct an accu-
rate set. Specific directions are unnecessary.

A thousand grain bottle will also be wanted. This
can be purchased in the shape of a regular "specific
gravity bottle;" its cost is $2.00. The practitioner can
readily adapt an ordinary bottle to the purpose, simply
selecting one of such capacity that when a volume 'of
one thousand grains of rainwater at 60° F. is placed
therein, the water shall rise part way in the neck, and
its place marked with a file, we have on hand some half-
dozen 1,000 grain bottles, which we have picked up from
time to time, and which are in regular use, the specific
gravity bottle being held in reserve as a standard, or
for the determination at times of the density of liquids.

Imprimis. — Let me recommend to the practitioner that
he eschew the entire system of weights as recognized

21 Microscopy.

322 HOW TO SEE WITH THE MICROSCOPE.

by the profession, and confine himself to that one simple
unit — the grain. This, in the case of chemicals, can be
adopted with perfect ease, and much confusion thus
avoided. In the following pages no other weight will
fee mentioned. Referring to liquid measures, the case
•would be somewhat modified, and we shall have occasion
probably to speak of fluid ounces, drachms, etc. Now
there are two fluid ounces in vogue; the one is known
as the English " imperial," and is equivalent to a volume
of distilled water at 60° F., weighing 437.5 grains.
This, also, is the ounce avoirdupois. The United States
standard fluid ounce is quite another thing. This is equal
to a volume of distilled water at 60° F., weighing 455.69
grains, sixteen such ounces making one pint. The United
States ounce will be the one referred to in this book,
"when speaking of fluid ounces and drachms, eight of the
latter being equal to one of the former. The practi-
tioner should keep in mind these differences between the
United States and the English fluid ounce, when reading
English authors.

O

In the selection of his chemicals for the preparation
of the standard solutions, the utmost attention must be
paid to their purity. They should not be bought at the
** nearest drug store." It will be always advisable to
purchase them from leading dealers. The formulas
which will be given relate only to pure chemicals. Due
attention also should be given to the manipulations,
that the chemicals shall not become contaminated. Even
after the standard solutions are successfully prepared,
the careless operator may ruin a solution by thought-

APPARATUS. 323

lessly pouring the remaining contents of the burette
(after an analysis) into the wrong bottle. The same
glass rod ought not to be used in different solutions
without being cleansed. Every bottle should have its
own stopper, and these should not become interchanged.
Every piece of apparatus used in an analysis should, at
the termination thereof, be immediately cleansed.

The practitioner will find it convenient to make his
several standard solutions in quantities of 3,000 grains.
With the exception of the one used for the determina-
tion of sugar, they all have reliable keeping properties,
and as 3,000 grains can be made with about as little
trouble as 1,000, it is an economy of time to do so.

Procure, if possible, suitable bottles for the standard
solutions, furnished with a " pouring lip." These are
so much handier in filling the burette. Ours were ob-
tained from an ink manufactory, and answer the purpose
perfectly.

Analysis for Urea — Standard Solution. — Weigh
thirty-eight and six-tenths grains of pure red oxide of
mercury and place the same in a large test tube, add a
little nitric acid, c. p., and apply the heat from the spirit
lump. The oxide will appear to crust and little inclined
to dissolve. By keeping up an uniform heat, mean-
while stirring with a glass rod, the oxide will become
gradually dissolved. Should it, however, become neces-
sary, add a little more acid carefully, little by little,
maintaining the gentle heat and stirring with the rod
until all of the oxide shall be dissolved, the object being
to use the least amount of acid possible. The process

324 HOW TO SEE WITH THE MICROSCOPE.

being" completed, pour the whole into a thousand grain
bottle, rinse two or three times with distilled water,
adding this to the measuring bottle, and finally add dis-
tilled water to make the whole to 1,000 grains. Let it
stand for a few hours, after which time should there
form a precipitate of the basic salt, add two or three
drops more of the- acid. The solution may now be
transferred to the regular bottle for use. Two hun-
dred grains of this standard solution are (should be)
equivalent to one grain of urea.

Baryta Solution. — In one bottle make a cold solution
saturated with nitrate of baryta; four ounces of dis-
tilled water will be sufficient. In another bottle satu-
rate eight ounces of distilled water (cold) with caustic
baryta. When the solutions are fully saturated, which
may be known by the baryta remaining in excess in the
twTo bottles, allow a little time for the two solutions to
become clear; then carefully decant as much as possible
of the nitrate solution into your regular bottle, and to
this add twice the volume of the caustic solution, the
two combined forming the baryta solution for use in
analysis.

Carbonate of Soda Paper. — In a bottle prepare a
saturated solution of carbonate of soda. When fully
saturated pour into a large dish or platter, provide
sheets of ordinary printing paper, saturate these and
suspend the sheets until quite dry; cut into strips one
inch wide by six or seven inches long-, and preserve in a
wide mouthed bottle fitted with a well-fitting stopper.

Measuring Bottle. — Procure one of the long and slim

APPARATUS. 325

four-drachm bottles found at almost any druggist's, say
with an interior calibre of one-fourth inch. Mark this
with a file at heights corresponding to 50, 66, 100 and
200 grains. This is easily accomplished with the aid of
the burette. The plain bottles Avithout a neck are to be
preferred.

The Analysis for Urea. — Take a sufficient quantity
of the urine, and if albumen is present clear it from the
same; next, pour into the measuring bottle to the 100
grail* mark. Transferring this to a common wineglass,
in a like manner measure 50 grains of the baryta solu-
tion ; add this to the other in the wine-glass, pour the
whole on a dry filter, receiving the filtrate in another
glass. Should the liquid come through clear, it is well ;
if not, it must be refiltered until it does. Three or four
filtrations at the most will generally accomplish the de-
sired end. While the filtering is in operation fill the
burette to the "0" mark with the standard solution.

With the measuring pipette transfer one-half drachm
of the clear filtrate to a clean wineglass, adding half its
quantity of distilled water. Have in readiness a strip
of the carbonate of soda paper and a glass rod. Deliver
the standard solution from the burette to the filtrate as
long as any precipitate is distinctly seen to form, stir
with the rod, and place a drop from the glass in contact
with the paper, waiting a moment to observe the reac-
tion. If the paper continues white, acid again from the
burette, and stir again, placing a second drop on the
paper, and thus continue carefully until the drop trans-
ferred to the paper strikes a yellow color. Now look

326 HOW TO SEE WITH THE MICROSCOPE.

among the previous drops on the paper and see if there
are any indications of the yellow. If so, you have used
too much haste, and the analysis must be repeated. If to
the contrary the yellow is only to be observed at the last
test made on the paper, the analysis is ended. Read the
burette, multiply this number by 12 -f- 100 and you will
have the number of grains to the fluidounce of urine.

It will be well, before making a practical use of the
standard solution, to test the same. Proceed thus :

Procure, say one-fourth ounce of pure urea. This can
be had of the leading druggists at a cost of about twenty-
five cents. Of this weigh carefully two grains, which
dissolve in 200 grains of water. Take 50 grains of the
solution and tritate as above. When the carb. of soda
paper strikes a yellow color, desist and read the burette.
Now the 50 grains of solution contained, of course, one-
half grain of urea, and the burette should, if the stand-
ard solution have been properly prepared, read at the 100
mark. If the reading should be less than the 100, the
solution is too strong, and must be weakened by the fur-
ther addition of distilled water. If, on the contrarj^,
the reading should be more than 100, the solution is too
weak, and more of the mercury must be prepared and
added. For the purposes of the practitioner there is
no necessity of being over precise. If the burette shows
but a small error, plus or minus, it will be sufficient to
note the fact on the label of the bottle, applying a
proper correction to the future analyses. In the exam-
ination of the reactions on the carb. of soda paper, es-
pecially in the evening, we find a hand-magnifier of
much service.

APPARATUS. 327

Chloride of Sodium — Standard Solution. — Dissolve
forty-four grains pure nitrate of silver in 3,000 grains
of distilled water; employ a clear white glass bottle
and set the same in the sunlight for eight or ten hours.
A dark brown or black precipitate will probably form ;
when this settles to the bottom, filter into a clean bot-
tle, decanting carefully so as not to disturb the sedi-
ment; 200 grains of this standard solution should equal
one grain of chloride of sodium. Before being put to
practical use the solution must be tested.

Solution of Chromate of Potash is made by saturat-
ing three or four ounces of distilled water; an excess
of potash remaining undissolved is not objectionable.

To Test the Standard Solution.. — Procure a nice
clean lump of " rock salt," crush, and select of the
cleanest, ten or fifteen grains ; powder roughly and dry
with care, using but gentle heat. When thoroughly
dry, dissolve two grains in two hundred grains of dis-
tilled Avater, and of this measure fifty grains into a
wine-glass, add a little water and one or two drops of
the potash solution. Fill the burette and tritate. The
addition of the first drops of silver to the salt solution
may be followed by the appearance of a red precipi-
tate, but on stirring with the glass rod this will re-
dissolve ; continue the addition of the silver little by
little, stirring well after each addition, until the further
delivery of the silver is followed by a permanent pre-
cipitate imparting a red color to the contents of the
wine-glass. This finishes the test, and if the standard
solution is of the proper strength, the burette will

328 HOW TO SEE WITH THE MICROSCOPE.

read at the one hundredth mark ; if too strong or too
weak, add silver or water as the case may demand, and
repeat the test. The indications of the burette furnish
a ready guide as to the amout of correction necessary,
hence the second test ought to be sufficient.

Analysis of Urine for Chloride of Sodium. — Filter
say one-half ounce of the urine, and with the measur-
ing pipette introduce one fluid drachm of the filtered
urine into a wine-glass, and add three volumes of dis-
tilled water, and also two or three drops of the satu-
rated potash solution. Now with a bit of litmus paper
test the reaction of the mixture ; it should be rendered
faintly alkaline by adding carbonate of soda, or dilute
nitric acid as may be found necessary. Fill the burette
and tritate according to the directions given above,
until the permanent precipitate makes its appearance.
Now read the burette, divide this number by twenty-
five which will give you the number of grains of
chloride of sodium per fluid ounce of urine.

Should the specimen of urine be very high colored
it may be somewhat difficult to detect the first appear-
ance of the permanent precipitate, hence the accuracy
of the analysis will be impaired. In such cases, there-
fore, it is better first to decolorize the urine; this is
tolerably well accomplished by adding a drop or two of
a solution of permanganate of potash, and with the
spirit-lamp bring the mixture nearly to the boiling
point. A brown precipitate will be observed which is
to be removed by filtration, and the filtrate used for
the analysis according to the preceding directions.

APPAEATUS. 329

Analysis for Chlorides Approximately. — Fill a
Marais graduated tube to the ounce mark with fil-
tered urine, make strongly acid with nitric acid; pro-
vide a solution ot nitrate of silver, forty grains to the
ounce of water; add an excess of this to the urine in
the tube, allowing the whole to remain quiet for twenty-
four hours. At the expiration of this interval the
volume of precipitate may be read from the graduated
scale, each ,2c.c. of precipitate will equal 0.19 grains
of chloride of sodium ; in the above approximate anal-
ysis the acid must not be omitted, otherwise a precipi-
tate of phosphate of -silver might vitiate the results.

Analysis for Phosphoric acid. — Dry carefully a suffi-
cient quantity of chemically pure nitrate of uranium,
using gentle heat; of this take 106 J- grains and add
3,000 grains of distilled water; 200 grains of this
standard solution equals one grain of phosphoric acid.

Solution of Acetate of Soda. — Four hundred grains
of acetate of soda are dissolved in six fluid ounces of
water, and to the solution add 800 grains of acetic
acid. The commercial article known as "JSTo. 8" will
answer.

Solution of Ferro -cyanide of Potassium is made by
dissolving one part of the salt in ten parts of water.

Test Solution. — Dissolve 50.4 grains of phosphate of
soda in 1,000 grains of water; 100 grains of this solu-
tion equals one grain of phosphoric acid.

To Test the Standard Solution. — Measure fifty grains
of the above test solution into a beaker; add one-fourth
volume of the acetate of soda solution, increase the

330 HOW TO SEE WITH THE MICROSCOPE.

volume of this mixture three-fold by the addition of
water; fill the burette with standard solution, and
have in readiness a white plate or saucer, 011 which
have been placed several separate drops of the ferro-
cyanide. Heat the contents of the beaker over the
spirit-lamp, and keeping1 the same tolerably warm,
tritate with caution, and when a drop from the beaker
on being placed in contact with the ferro-cyanide
strikes a brown color, the analysis is ended ; and if the
standard solution is of the proper strength, the burette
will read at the 100 mark. Any error of standard
solution noticed is to be corrected and the analysis re-
peated with the standard solution as amended.

Analysis of Urine for Phosphoric acid. — With
the pipette measure two fluid drachms of the urine
into a beaker, and to this add one-half drachm of the
acetate of soda solution, also an extra drachm or so of
water ; have ready the white plate and the ferro-cyanide
solution; warm the contents of the beaker over the
spirit-lamp, and maintaining the heat, tritate as in the
above test; continue the addition of the standard solu-
tion until the drop from the beaker when in contact
with a drop of the ferro-cyanide shall strike a brown
color, which terminates the analysis. Read the burette,
the number shown divided by fifty will indicate the
number of grains of phosphoric acid to the fluid ounce
of urine.

Analysis with the Marais Approximate Tubes. —
The tube is to be filled to the ounce mark with filtered
urine, add also two drachms of the acetate of soda solu-

APPARATUS. 331

tion, afterwards add an excess of a solution of nitrate
of uranium (one to ten): placing the thumb over the
end of the tube ; mix thoroughly and allow the tube to
remain quiet for twenty-four hours, after which time
the volume of precipitate may be read of, ever 2cc
— .016 grains of phosphoric acid.

Analysis for Earthy Phosphates, using the Marais
Tubes. — Fill the tube to the ounce mark with filtered
urine as above, add an excess of strong liquor ammonia;
mix well and set aside for twenty-four hours, at the
end of this interval note the volume of precipitate;
each 2cc will correspond to .06 grains of the earthy
phosphates.

Analysis for Sulphuric acid Standard Solution. — In
3,000 grains of distilled water, dissolve forty-five and
three-fourth grains of pure chloride of barium; 200
grains of this standard solution are equivalent to one
grain of sulphuric acid. If the solution be prepared
with due care, it may be used without special testing
as it cannot be very well tritated.

Solution of Sulphate of Soda. — One part of soda to
ten of water.

Analysis of Urine for Sulphuric acid. — With a
pipette measure two fluid drachms of urine into a
beaker, dilute this with twice as much distilled water,
adding also two or three drops of hydrochloric acid ;
bring the beaker over the spirit-lamp until the contents
become hot, fill the burette with the standard solution ;
deliver from the burette into the beaker a few drops
which will cause an instant precipitate ot the sulphate

332 HOW TO SEE WITH THE MICROSCOPE.

of baryta ; this will gradually sink to the bottom of
the beaker; continue thus the addition until no further
precipitate can be detected by the eye. By waiting a
few moments the liquid above the precipitate will be-
come clear, when another drop or two of the standard
solution may be added. Should this cause a further
precipitate, continue in like manner to add the standard
solution; when no further precipitate forms, place a
few drops of the sulphate of soda solution in one of
the smallest test tubes, and to this add a drop or two
from the beaker; if a white precipitate appear in the
test tube, the standard solution has been added to the
beaker in excess ; and if the precipitate be very dense,
the analysis will have to be repeated, using greater
care towards the latter part. The number of grains
finally shown by the burette, divided by fifty, indicates
the number of grains of sulphuric acid to the fluid
ounce of urine.

The final determination in this analysis as to the pre-
cipitation of all the sulphuric acid renders this tritation
somewhat more troublesome to the beginner than the
preceding. The practitioner should therefore, by re-
peated trials, become acquainted with the details. In
examining the test tube as to the precipitate, it should
be held to strong light, and a hand magnifier we have
found to be of material assistance.

Analysis for Sugar — Standard Solution. — Dissolve
51.98 grains of pure sulphate of copper in 500 grains of
distilled water. Keep this in a bottle by itself.

Dissolve caustic soda in distilled water until the spe-

APPARATUS. 333

cific gravity becomes 1.12, or the specific gravity imiy
be determined by the use of Baume's hydrometer, which
should float at 16J°. To each 1,000 grains of this solu-
tion add 259.90 grains of purecn/sto^ecZRochelle salts.
This constitutes the caustic solution.

One volume of the copper solution mixed with two
volumes of the caustic solution forms Fehling's Stand-
ard Solution, 200 grains of which are equivalent to one
grain ot sugar.

These solutions must be kept separate until wanted
for use, mixing only the quantity required from time to*
time. The copper solution is quite stable, but the other
is liable to deteriorate by keeping. It will be advisable
for the practitioner to use the caustic solution from an
ounce bottle fitted with a tight stopper, which can be
refilled from time to time, the stock bottle being kept
in a cool, dark place. On mixing the two together a
precipitate forms which will immediately disappear on
shaking. Should, on boiling the same, the liquid retain
a clear blue color, it is in good condition. Heat should
always thus be applied in advance. By complying with
the directions given, the caustic solution can be kept in
order for years ; and it is well to make enough at once
to last for at least a year, and the physician is reminded
that this Fehling's test for sugar is daily in demand.

Test of Standard Solution for Sugar. — Dissolve four
grains of pure grape sugar in 400 grains of water.
This solution should always be used when freshly made.
In the preceding analysis it will be observed that the
burette has been filled with the standard solution. Now

334 HOW TO SEP: WITH THE MICROSCOPE.

in the operation for sugar this is not the case. There-
fore fill the burette to the " 0 " mark with the graduated
solution of grape sugar. Into the measuring bottle
before described measure 66 grains ot'the copper solu-
tion, the proper height being marked on the bottle with
a file. Add of the copper solution to that in the meas-
uring bottle to make the volume equal to 100 grains.
We then have 100 grains of the standard solution mixed
for use, and which are equivalent to J grain of sugar.
Pour the standard solution from the measuring bottle
into the largest test tube ; rinse the former with a little
water, and add this to that in the test tube, bringing
the latter over the spirit lamp ; heat to the boiling point,
and notice, first, if the standard solution retains its
clear blue color; if so, proceed to tritate, adding from
the burette a few drops at a time, bringing the mix-
ture, after each addition, to the boiling point. Con-
tinue thus, adding from the burette until the blue
color of the mixture in the test tube shall have almost
entirely disappeared. At this stage of the decom-
position of the copper the mixture in the tube will
have become thick and of a greenish yellow color, and
will show but little disposition to settle clear. Now
add cautiously a few drops from the burette ; bring to
the boiling point again, and, holding the tube in an in-
clined position near a sheet of white paper, observe the
thin edge of the liquid as to color. Should there appear
a trace of the blue yet, continue the addition from the
burette, and also the heat, until the last trace of the
blue shall have disappeared. Eesting the tube in a ver-

APPARATUS. 335

tical position, wait a moment or two, and if the reduc-
tion of the copper be complete, the sediment will sink
in a very short interval of time, to the bottom of the
tube ; and if care has been taken not to overdo the thing,
i. e., introducing more than was necessary from the
burette, the analysis is completed and the burette may
be read.

Now the 100 grains of the standard solution in the
test tube would require } grain of sugar for its reduc-
tion, and 50 grains of the solution in the burette will
contain J grain of sugar. The burette should therefore
be lead at 50°. The student is advised to repeat the
operation several times until he shall have become
familiar with the reactions. The quantity of test solu-
tion is ample for this. If, after satisfactory trials, it
shall be found that the standard solution is to strong or
too weak, water or copper may be added to the copper
solution without making any change in that of the
caustic, and the test should again be repeated.

Analysis of Urine for Sugar. — Prepare the standard
solution for use just as has been directed; i. e., measur-
ing 66 grains of the caustic solution, and adding the
copper solution to make the volume of 100 grains.
Pour, as before, into the largest test tube, rinsing the
measuring bottle, adding the " wash " to the contents
of the tube. A very little clear water may also be added
to the tube. Fill the burette to the " 0 " mark with
the urine to be analyzed, bring the test tube over the
spirit lainp, and heat to ebulution. Now go on and
tritate just as directed in the preceding test, observing

336 HOW TO SEE WITH THE MICROSCOPE.

due care, when near the complete decomposition of the
copper. When this shall be obtained, and the blue
color of the standard solution has disappeared, the sedi-
ment in the tube being also inclined to settle quickly,
the burette may be read.

Now, to determine the amount of sugar from the
reading- of the burette is a simple question of the " rule
of three," suppose that the number marked by the bu-
rette to have been 228, then it follows that 228 grains
of the urine contained J grain of sugar; Hence 458
(one ounce) of the urine would contain 1 grain of sugar,
or, as we would say, " one grain per ounce." It may
be well to suggest to those who have allowed their
mathematics to become a little rusty, that even in solv-
ing proportions, simple as are the computations, that it
is necessary to look after one's decimal points. Thus,
in the above example, the expression would be — 456
X 0.50, 4- 228 = unity.

Use of the standard solution in the ordinary testing
for sugar. The practitioner will very often have occa-
sion to simply test for the presence of sugar, when the
exact amount is not necessary. In fact, after becoming
thoroughly familiar with the behavior of the chemicals,
he will be enabled to give a close guess as to quantity.
The urine should in all cases be cleared from albumen.
To merely detect the presence of sugar it is only neces-
sary to pour a dozen drops or so of the copper solution
into one of the largest test tubes (these are always bet-
ter when there is boiling to be done), and to add twice
the volume of the caustic solution. Bring- to the boil-

APPARATUS. 337

ing point, and add urine to the tube directly, continuing
such additions and bringing1 to the boiling point sub-
stantially as in performing the regular analysis. If,
when the amount of urine thus introduced shall be equal
to the original volume of the test solution, and there be
no change of color, it may safely be assumed that sugar
is not present.

Even when the regular analysis is contemplated, the
preliminary trial test should be instituted. For instance,
we do not care to attempt the regular analysis, when
by the rough test we are assured that there is no sugar
in the specimen. Again, when, by the trial test, it shall
be found that sugar is present, and in large amount,
then it may sometimes be better to dilute the urine
with an equal, or even six times its volume of water;
of course, allowing for this reduction in the computa-
tions after reading the burette; the accuracy of the*
analysis is enhanced by the dilution ot the urine. It
may be further remarked that different specimens be-
have somewhat differently. The directions given will,
however, be found ample, and the practitioner having
frequent use for the sugar test in a short time becomes
perfectly at ease with the manipulations.

Analysis for Albumen. — The volumetric method, one
of "trial and error," involving several filtrations, is
somewhat tedious ; too much so for the practical pur-
poses of the medical practitioner. The author was
hence induced to experiment with the "Marais" ap-
proximate tubes comparing results with those obtained
by two of the regular methods. These were so far sat-

22 Microscopy.

338 HOW TO SEE WITH THE MICROSCOPE.

isfiictory as to lead to the employment of the approxi-
mate tubes in his general practice ; and the degree of
accuracy afforded by the use of these tubes is quite equal
to the ordinary demands of the medical profession.
The principal source of error arises, as we believe, from
the fact that the coagulated albumen will at times pack
closer in the tube than at others. By using three or
four tubes in one and the same analysis, taking the
mean of the results, the approximate process will, in
most instances, be all that can be desired. Proceed as
follows :

In a clean evaporating dish, or a Florence flask, coag-
ulate by heat three fluid ounces of the urine to be
tested; set aside until nearly cold; shake well; now
take three marais tubes, fill the first full, also the
second with the treated urine and coagulum; pour the
remainder into the third tube, rinsing the dish with a
little water, adding the wash to the several tubes. The
three tubes can be thus made to contain the entire
coagulum from the three ounces of urine ; set aside for
twenty-four hours, after which time read the several
tubes; add the readings together and divide by three,
and every two whole cubic centimetres will represent
one grain of albumen to the ounce of urine.

In the daily routine it will often suffice to use but
one tube, in which case all that is necessary will be to
coagulate a single fluid ounce of the urine; when cool,
shake, and pour into the approximate tube, rinsing the
dish as before, adding the wash to the tube ; at the end
ot twenty-four hours read off the amount of coagulum ;

APPARATUS. 339

every two whole c. c. will equal one grain of albumen
to the ounce of albumen.

Reaction. — Urines being at times either acid, neutral,
or alkaline, it is often interesting, not only to observe
as to the fact, but also as to the degree of acidity or
alkalinity; to accomplish this prepare the following
solutions:

Test Solution for Acidity. — In 1,000 grains of dis-
tilled water dissolve ten grains of pure hydrate of soda.

Test Solution for Alkalinity . — In 1,000 grains of
distilled water dissolve 15.75 grains of pure oxalic acid.
Equal volumes of these two solutions will exactly neu-
tralize each other.

To Test the Degree of Acidity in a Sample of Urine.
— Fill the burette with the soda solution ; measure one-
hult fluid ounce of the urine into a wine-glass; deliver
the soda from the burette into this a few drops at a
time, stirring well after each addition and testing writh
litmus paper; when the mixture fails to affect the
latter, read the burette twice, the figures read will indi-
cate the number of grains of the solution employed
required to neutralize a fluid ounce of the urine. To
test for alkalinity proceed as above, using the acid solu-
tion in place of the soda, and also red litmus paper in
place of the blue. The daily variations in any particu-
lar case can in this manner be determined and recorded.

Proportion per Ifluid Ounce of certain of the Urinary
Constituents.

The estimates given in this part of the table are roughly ap-
proximative, and represent the widest variations consistent with

340

HOW TO SEE \V1TH THE MICROSCOPE.

normal conditions. Th.e variations, always considerable, are
particularly marked as regards the uric acid .

Urea 6'50 to 10'50 grains.

Chlorine (1*30 to 3'60 ars. of chloride of sodium) 0*80 " 2'15 •»

Sulphuric acid (1'3U to 3'20 frrs. of sulphates) 0'66 " 1'62 •»

Phosphoric acid (2-10 to 4-00 grs. of phosphates) 1T7 *• 2-35 "

Do do combined with alkalies (phosphate of

soda and phosphate of magnesia) 0'78 '* 1'40 u

Do do combined with earths (phosphate of
lime and ammonio-magnesian phos-
phate) 0-39 " 0-85 "

Uric acid (0.40 to 0'70 grs. of urates) 0*23 " 0'40 "

TABLE FOR REDUCING THE INDICATIONS OF A GT.ASS URINOMETER TO
STANDARD TEMPERATURE (60° Fahr.) WHEN THE SPECIFIC GRAVITY HAS

BEEN TAKEN AT A HIGHER TEMPERATURE. (BlRD, Urinary Deposits.

etc., Philadelphia, 1859 p. TJ.)

Tempera-
ture and
degree.

No. to be
added to
the indi-
cation.

Tempera-
ture and
degree.

No, to be
added to
the indi-
cation.

Tempera-
ture and
degree.

No. to be
added to
the indi-
cation.

60

o-oo

69

0-80

78

1-70

61

0-08

70

0.90

79

1-80

62

0-16

71

1-00

80

1-90

63

0-24

72

1-10

81

2-00

64

0-32

73

1-20

82

2-10

95

0'40

74

1-30

83

2-20

66

0'50

75

1-40

84

2-30

67

0-60

76

1-50

85

2-40

63

0-70

77

1-60

APPENDIX.

As a matter of convenience to the student we present
the addresses of American dealers in Microscope Stands,
Objectives, etc. The list is compiled from the various
catalogues and other sources of information which hap-
pened to be in our possession. It is therefore probably
incomplete, but nevertheless will be found to comprise
most, if not all of the leading dealers. Of the latter,
those marked with an asterisk (*) issue illustrated cat-
alogues, which can be obtained on application, free of
expense :

NAMES AND ADDRESS OF DEALERS IN MICROSCOPES, OBJECT-
IVES, ETC., ALPHABETICALLY ARRANGED.

(*)Batisch & Lomb Optical Company, 37 Maiden
Lane, New York; factory at Rochester, New York.

(*)R. & J. Beck, (London); American Agency in
charge of W. H. Walmsley, Chestnut street, Philadel-
phia, Pa.

(*)W. H. Bulloch, 126 Clark street, Chicago, 111.

F. J. Emmerich (Importer), 38 Maiden Lane, New
York.

E. Gundlach, L. E. Sextcn, agent, Rochester, New
York.

(*)T. H. McAllister, 49 Nassau street, New York.

Pike (Dealer), 518 Broadway, New York.

341

342 HOW TO SEE WITH THE MICROSCOPE.

(*)James W. Queen & Co., 924 Chestnut street, Phil-
adelphia, Pa.

William A. Kogers (Micrometer Plates, etc.,) Cam-
bridge, Mass.

(*)Messrs. C. A. Spencer & Sons, (Objectives, Ac-
cessories, etc.,) Geneva New York.

L. Schrauer, 50 Chatham street, New York.

(*)J. W. Sidle & Co., Lancaster, Pa.

(*)Robert B. Tolles, Hanover street, Boston, Mass.
Charles Stoclder, Agent, Devonshire street, Boston,
Mass.

(*)George Wale, Patterson, N. J. George Wale &
Co., Hoboken, N. J., Agents.

(*) William Wales, Fort Lee, New Jersey.

(*) Joseph Zentmayer, 147 South Fourth street, Phil-
adelphia, Pa.

The following price list of stands, etc., is only in-
tended to include those previously described in this
book. Several of the makers therein mentioned manu-
facture various models not included in our list. The
stands ot the Messrs. Spencer's have been intention-
ally omitted, as we learn that they are now devoting
their entire attention to the production of objectives.

The list of objectives is similarly incomplete. With
the glasses of Messrs. Tolles and Spencer we have had a
large experience. Several months ago the Messrs. Bausch
& Lomb sent us a line of their objectives for study,
all of which, after working with the same more or less
for nearly a year, proved reliable glasses for their cost.

APPENDIX. 343

The entire list may be understood to include only such
objectives as we have used to a greater or less extent
in practical work, and of which we can therefore speak
from experience, and without prejudice to other reliable
makers.

We earnestly advise the student contemplating the
purchase of object glasses, especially when ordering
the same to be made by the optician, to seek the advice
of some expert friend. Protection is thus afforded both
to the maker and the buyer, and it has often happened
that the latter, through sheer incompetency, returns a
really fine glass to its maker, with the assertion that it
has proved unsatisfactory. While on the other hand,
especially in glasses of high balsam angles, there IS a
choice in the work of the very best makers. The ex-
pert, too, will render valuable assistance in specifying
the exact kind of objective desired.

MICROSCOPE STANDS, BY W. H. BULLOCH, NO. 126
CLARK STREET, CHICAGO, ILL.

Large best stand, Al, binocular, iris diaphragn, with the

latest improvements, draw-tube, 5 eye pieces $300 00

Same as above, but monocular, iris diaphragm, with three

eye pieces 250 00

Polished mahogany case, with side case for accessories. 25 00
Small best stand, A. B., binocular, 4 eye pieces and iris

diaphragm 225 00

Monocular, two eye pieces and iris diaphragm 175 00

Polished mahogony case 20 00

44 D " stand, all brass, 2 eye pieces and case 75 00

41 D " stand, ail brass except the base, 2 eye pieces and

case.., 67 00

344 HOW TO SEE WITH THE MICROSCOPE.

MICROSCOPES A!S"L> OBJECTIVES BY THE BAUSCH &
LOMB OPTICAL COMPANY.

The Professional Microscope, with the following acces-
sories : Hemispherical immersion condenser and ob-
lique light projector, plain and concave mirrors, sub-
stage, receiving accessories of standard English size,
two revolving diaphragms, sub-stage with internal
•"• society screw," 2 slot diaphragms for mirror, 3 Gund-
lach's periscopic eye pieces (B, C and D), four object-
ives, viz : 2-inch, l-5th inch, 3-4th inch and l-8th inch
immersion, with adjustment for cover, magnifying
powers from 30 to 800 diameters, eye piece micrometer,
camera lucida, bull's eye condenser, the whole in
upright walnut case, with handle, lock and key, and
drawer for accessories $200 00

Large Student's Microscope, plain and concave mirrors,
sub-stage of extra size to receive standards, English
accessories, revolving diaphragm, etc., all attached to
the swinging mirror bar ; sub-stage and mirror are re-
movable ; three eye pieces, A, B and C, three object-
ives, 2-inch, 3-4th inch and l-5th inch, magifying from
22 to 375 diameters, eye piece, micrometer, camera
lucida, in upright walnut case, with handle, lock and
key, and drawer for accessories 90 00

Family Microscope, concave mirror, adjustable for ob-
lique light, one (B)eye piece, one first-class achromatic
objective (one-half inch dividing) powers, 50 and 100
diameters, in upright walnut case, with handle, lock
and key 20 00

The Messrs. Bausch & Lomb have brought out a new model
which they term the Physicians' Stand, which may be thus de-
scribed :

Large, heavy cast iron foot, rack and pinion for coarse
adjustment, draw-tube, allowing 2 1-2-inches shorten-
ing, fine adjustment by a new frictionless motion, large
hard rubber stage, sub-stage of standard size, carrying

APPENDIX. 345

three diaphragms, which, when pushed up, will closely
reach the object slide, plain and concave mirrors, ar-
ranged so that their distance from the object may be
varied, 2 eye pieces, A. and C, 2 objectives,3-4ths inch
and l-5th inch, magnifying powers, when the tubes are
completely drawn out, from 50 to 375 diameters, eye
piece, micrometer and camera lucida, in upright wal-
nut case, with lock and key 60 00

The past twelve-month has witnessed unusual activity on the
part of microscope makers. Mr. Zentmayer, in the production
of his " Histological," (as also the advent of the Acme Stand)
stimulated other makers to increased energy in the production
of small, low-priced and reliablt stands capable of performing
the work of larger and costly instruments.

At the late (August, 1880) meeting of the American Society
of Microscopists, held at Detroit, Michigan, two medium-priced
stands were exhibited which were regarded bv competent
judges as being quite equal to the Acme Stand. One of these
was made byfMr. Bullock, of Chicago, and its cost — as near as
I can learn- will be about $50.

The other stand referred to was exhibited by the Messrs.
Bausch & Lomb, of Rochester, N. Y. It is called the *" Inves-
tigator." Messrs. B. & L» have furnished the author with the
following description of

THE INVESTIGATOR MICROSCOPE.

lu this stand we confidently claim to have reached a higher
degree of perfection than is possessed by any one approximat-
ing it in price. We have combined in it the qualities of a
first-class and high-priced stand, and at no sacrifice of its
working qualities. The different parts are ingeniously com-
bined, are strong and lirm, and in the parts subject to friction
we have introduced, as much as possible, new compensating
bearings, which insure the retention of smooth and reliable
movements with any amount of work. Working microscopists
will understand the value of this quality. When contracted it
stands but 11 high, but can be extended to 18 inches.

346 HOW TO SEE WITH THE MICROSCOPE.

The base is of the tripod form, neatly japanned ; pillar and
arm of brass, connected by a solid joint, which allows inclina-
tion of body to any angle ; rack and pinion for coarse adjust-
ment, tine adjustment by our patent frictionless motion ; main
tube with two draw tubes. This is an entirely new feature in
microscopes, which is an unquestionable improvement. It per-
mits the use of standard length of tube for quick adjustment
in outside tube, same as in instruments without rack and pinion
adjustment ; the same for any low power objective and the use
of amplifier in either combination. The outside tube has a
broad gauged screw, and adapter with society screw. The stage
lies in the same plane as center of movement for mirror, is of
brass, and has concentric, revolving motion with removable
clips. It is thin to allow great obliquty, and as it rests upon a
strong projecting arm, is perfectly firm under any manipulation.

The mirror bar swings with a peri'ectly easy but firm motion,
upon one bearing to any obliquity below, and above the stage
for the illumination of opaque objects, and has affixed to it a
secondary bar, to which the mirror is attached and which allows
the separate use of the latter in any position of the sub-stage.
It is provided with a sliding arrangement, whereby the mirror
may be moved to and from the object. The mirrors are plain
and concave, and of large size. The substage is adjustable
along the mirror bar, and entire removable. It contains a
diaphragm which may be brought directly under the stage. The
ring is of standard size and is easily centered by a set screw.
The stand is furnished with an eye piece of any power.

In black walnut case, with receptacles for eye pieces and
objectives, drawer for accessories, handle and lock, price $40.00.

Same, with C Eye Piece, arranged for micrometer, camera,
lucida, micrometer, 3-4 inch and 1-5 inch objectives, $65.00.

BAUSCH & LOME OBJECTIVES.

Deg. Price.

2inch 18 $12 00 .

2inch 12 600

linen 36 2000

linch 20 600

APPENDIX. 347

Deg. Price,

8-4inch 27 800

l-2inch 72 2200

1-2 inch 40 9 00

4-10 100 20 00

3-10 75 11 00-

1-4 100 .', 14 00

1-5 108 1500

1-6 inch 180 Adjusting 30 Oft

1-8 Immersion 180 Adjusting 4000

MICROSCOPES OF THE MESSRS. R. & J. BECK, OF
LONDON. AMERICAN AGENCY IN CHARGE OF
W. H. WALMSLEY, ESQ , 1016 CHESTNUT STREET,
PHILADELPHIA, PA.

Popular Microscope stand, binocular, with one pair of
eye pieces, concave mirror, diaphragm, forceps, glass
plate, pliers, etc $65 Oa

Same, but monocular 40 00

Economic Microscope, as furnished by the makers, mo-
nocular, with sliding coarse adjustment, 1 inch and
1-4 inch object glasses, 1 eye piece, concave mirror,
condensing lens, glass plate with ledge, brass pliers
and diaphragm, in mahogany case 35 00-

The same, with rack and pinion, for coarse adjustment,
concave and plane mirrois, stage forceps, etc., in ma-
hogany case 50 00

(Both of the above stands are fitted with fine adjust-
ment screw.)

Extra eye pieces, each 4 00-

The Messrs. Beck have just published a large and com-
plete illustrated catalogue of their microocopes and
other scientific instruments, which they furnish to any
one on application. Among their later models of mi-
croscope stands we notice the u New National," cost-
ing, with one eye piece, concave and plane mirrors,
diaphragm, stage forceps, glass plate pliers, etc 40 OO1

Mahogany cabinet for the same 10 00

348 HOW TO SEE WITH THE MICROSCOPE.

Since the chapter on stands was written we have received the
following description of

BECK'S INTERNATIONAL MICROSCOPE STAND.

The improved large best or international microscope stand
has a tripod (A) for its base, upon which is placed a revolving
fitting (B), graduated to degrees, by which means the micro-
scope can be turned round without its being lifted from the
table, and the amount of such rotation registered ; upon this
fitting two pillars are firmly fixed, and between them the limb
(0) can be elevated or depressed to any angle, and tightened in
its position by the lever (D). The limb carries at one end the
body (E) (binocular or monocular) with eye-pieces and object-
glasses; in its centre the compound stage (F), beneath which is
the circular plate, sliding on a dove-tailed fitting, and moved up
and down by the lever (Z), and carrying the supplementary body
or sub-stage (G); and at the lower end a triangular bar carrying
the mirror (H). Each of these parts requires a separate
description.

The binocular body consists of two tubes, the one fitted in the
optical axis of the microscope, and the other oblique. At their
lower end and immediately above the object-glass there is an
opening, into which a small brass box or fitting (I) slides; this
box holds a prism so constructed that when slid in it intercepts
half the rays from the object-glass, diverts them from their
direct course, and reflects them into the additonal or oblique
tube. To the prism-box is attached a spring-catch, which,when
pressed in, permits of the removal of the prism-box ; but this is
only needed for cleaning, as, when the box is drawn back to the
distance allowed by this spring, the prism in no way interferes
with the field of view, and all the rays pass up the direct body,
and the microscope is converted into a monocular one.

The upper or eye-piece ends of the tubes are fitted with racks
and pinion for varying the distances between the two eye-pieces
to suit the differences between the eyes of various persons ; and
arrangements are made for racking out one tube more than the
other, to suit irregularities or inequalities between the eyes of
the observer.
This body is moved up and down with a quick movement by

APPENDIX. 349

means of the milled heads (K), and with a very delicate and fine
adjustment by the milled head (L). This milled head works
against a lever, which moves a slide independent of the rack-
movement, and gives an adjustment at once certain and
decided.

The compound stage is of an entirely new construction : the
object is most frequently merely placed upon it, but, if neces-
sary, it can be clamped by carefully bringing down the spring-
piece (M), the ledge will slide up or down, and the object may
be pushed sideways ; this arrangement forms the coarse adjust-
ment. Finer movements in vertical and horizontal directions
are effected by means of two milled heads (N" and O), the screws
attached to which are kept up to their \vork by opposing springs
so as to avoid all strain or loss of time. The whole stage
revolves in a circular ring by the milled head (P), or this can be
drawn out, and then it turns rapidly by merely applying the fin-
gers to the two ivory studs (Q Q) fastened to the top plater
which is divided into degrees to register the amount of revolu-
tion. The stage is attached to the limb on a pivot, and can be
rotated to any angle, which angle is recorded on the divided
plate (R), or can be turned completely over, so that the object
can be viewed by light of any obliquity without any interfer-
ence from the thickness of the stage.

Beneath and attached to the stage is an iris diaphragm (S),
which can be altogether removed, as shown in the illustration,
from its dove-tailed fitting, so as not to interfere during the
rotation of the stage. The variations in the aperture of this
diaphragm are made by a pinion working into a racked aic and
adjusted by the milled head (T).

Beneath the stage are two triangular bars (U V), the one
revolving round and the ocher rigid in the optical axis of the
instrument. On the former the sub-stage (G), carrying all the
apparatus hereafter described for illumination and polarization,
fits, and is racked up and down by the milled head (W); the
mirror also, if desired, slides on the same bar ; the revolving
motion to this bar is given by the milled head (X), and the
amount of angular movement is recorded on the circle (Y),
whilst the whole of this part of the stand is raised and lowered

350 HOW TO SEE WITH THE MICROSCOPE.

Concentric with the optical axis of the instrument by the lever
(Z),and the amount of such elevation or depression is registered
on a scale attached to the limb. This bar can be carried round
and above the stage, and be thus used for opaque illumination.

The lower triangle bar (V) carries the mirror (H), or a right-
angle prism, when the illumination is required to be concentric
with the optical axis of the instrument, and independent of the
movements of other illuminating aparatus.

The mirror- box contains two mirrors, one flat and the other
•concave ; it swings in a rotating semi-circle attached to a
lengthening bar, which enables it to be turned from one side to
the other, and revolves on a circular fitting for giving greater
lacilities in regulating the direction of the beam of Jight
reflected, the whole sliding upon either of the triangle bars, pre-
viously referred to, and made to reverse in the socket (a) so as
to bring the centre of the mirror concentric with the axis of the
microscope in either case.

As the mirror alone is insufficient for many kinds of illumin-
ation, some provision has to be made for holding various pieces
of apparatus between the object and the mirror. For this pur-
pose a supplementary body, or sub-stage, is mounted perfectly
true with the body, and is moved up and down in its fitting by
rack and pinion connectpd with the milled heads (W). This
sub-stage, to which reference has already been made, is now re-
garded as one of the most important parts of the achromatic
microscope; in it all the varied appliances for modifying the char-
acter and direction of the light are fitted. But a few years since
it was considered sufficient for this part of the stand to be con-
structed so as to move up and down perfectly coincident with
the optical axis of the instrument, and for that purpose it was
racked in a groove planed out on the same limb as that on the
upper end of which the optical portions were carried. But latelv
microscopists have shown the desirability of affording every
facility for lateral angular adjustments ; and this has led to the
sub-stage being attached to an arc (b) working in tbe circular
plate (Y), and moved by a rack and pinion (X), whilst the
amount of such angular movement is recorded on the upper sur-
face of the plate (Y). Having once fixed the angular direction

APPENDIX. 351

of the light, the focussing of it depends upon the lever (Z),
which moves the circle up and down, and with it the arm carry-
ing the illuminating apparatus in the optical axis of the instru-
ment. 80 long ago as 1854 Mr. Grubb, of Dublin, called atten-
tion to the advantage of mounting the illuminating apparatus
on a revolving arm or arc, which he thus describes in his pro-
visional specification for improvements in microscopes. No.
1477, 5th July, 1854 : — " My third improvement consists in the
addition of a graduated sectorial arc to microscope concentric
to the plane of the object " in situ,"' on which either the afore-
said prism or other suitable illuminator is made to slide, thereby
producing every kind of illumination required for microscopic
examination, and also the means of registering or applying any
definite angle of illumination at pleasure." With but slight
•modification, this is the plan adopted in this stand.

The sub-stage is also fitted with complete centering and rotat-
ing adjustments, the latter having a graduated circle attached,
and fittings for carrying Barker's series of selenites, blue glass
disks for modifying the light, etc. In all the requirements of an
instrument of precision, and fully meeting the wants of the
most advanced modern workers, it is confidently believed that
this new stand has no rival.

The price of the International Stand, Binocular, with five eye-
pieces, concave and plane mirrors, and right angle prism, stage
forceps, pliers and glass plate with ledge, is . . $325.00

The price of the International Stand, Monocular, with three
«ye-pieces, olid the same fittings as above, is, . . $275.00

(The Messrs. Beck manufacture several grades of objectives,
as will be seen by reference to their published catalogue.)

J. W. SIDLE & CO., LANCASTER, PA., ACME MICRO-
SCOPES AND ACCESSORIES.

We here quote the prices of the Acmes, and a few of the

more important accessories.

3a. Acme Monocular, with brass tripod base, rotating
stage, iris diaphragm and substage fitting with Society
screw for using objectives as condensers ; in walnut
case with lock and handle, and drawer for accessories, $ 50.00

352 HOW TO SEE WITH THE MICROSCOPE.

36. Acme Binocular, with one pair oculars, and outfit as
above . . 75.00

3c. Acme Monocular, as above, with # objective of 32°
and i of 100°, and small bull's eye condenser, . . 75.00

3d. Acme Binocular, as above, with f of 32°, i of 100°
and bull's eye, . 100.00

2a. Large Acme Monocular, rotating glass stage, sub-
stage, with rack and pinion, in polished mahogany case
with side case for accessories, 100.00

26. Large Acme Binocular, same as above, with addition-
al nose-piece, as per circular, 135.00

2c. Large Acme Monocular, as above, with mechanical
stage and 2 pair oculars, 135.00

2d. Large Acme Binocular, as above, with mechanical
stage and 2 pair oculars, 170.00

PRICES OF ACCESSORIES.

Mechanical stage for Acme No. 3, .... $16.00
Walnut base with lamp and adjustable stand, with brass
fitting to receive lower end of pillar, converting the Ac-
me into a Class Microscope, 5.50

Camera Lucida, 5.50

Neutral Tint (Beale's), 3.00

Iris Diaphragm, 4.50

Sub-stage fitting for using objectives as condensers, . l.OiJ

Woodward's prism, unmounted, 1.50

" mounted to screw in stage, . . 4 00

Mechanical Stage, 25.00

Sliding Object Carrier, fitted to stand, .... 4.00

Paraboloid, plain, 8.50

Parabolic Illuminator, 8.50

Polarizer for Acme, selenite screwing in stage, to rotate

independently of Nichol prism, 13.50

Polarizer, best, with large prism, 18.00

Mechanical Finger, 6.50

Solid Ocular, i, |, i inch, .... 8.00

APPENDIX. 353

CONGRESS TURN TABLE.

This table has made a reputation for itself. Retail
price $6.50

PRICES OF ACME SERIES OF OBJECTIVES.

2 inch, 15° ... $13.00 3-10 inch, 115° non adjust-
able, . . $16.00

H " 18° ... 14.00 3-10 u 115° adjustable, 20.00
1 " 36° ... 15.00 1-4 " 100° non-adjust-
able, . . 14.00

I " 32° ... 12.00 1-5 " 120° non-adjust-
able, . . 16.00

I " 36° ... 15.00 1-5 " 120° adjustable, 20.00
i " 60° . . . 14.00 Other lenses quoted in

Catalogue.

MICROSCOPE OBJECTIVES, BY MESSRS. C. A. SPENCER
& SONS, GENEVA, N. Y.

FIRST CLASS.

Size. Deg. Price.

3inch 13 $1800

2inch 20 2500

1 inch 50 4500

2-3inch 47 3200

1-2 inch 100 Adjustable 50 00

1-4 inch, dry and immersion 180 6500

1-6 inch, " " 180 7000

1-8 inch, " u 180 7000

1-10 inch, " " 180 8000

J-16inch, " " 180 11500

PROFESSIONAL SERIES.

3inch 13 $1800

2inch 16 1800

1 inch 33 1800

2-3inch 36 2000

23 Microscopy.

354 HOW TO SEE WITH THE MICROSCOPE.

l-2inch 65 2500

1-4 inch, Adjustable 115 2400

1-6 inch, " 175 Dry and immersion 34 00

1-8 inch, " 175 " " 40 00

1-15 inch, " 175 " " 5000

STUDENTS' SERIES.

Sinch 8 $600

2inch 10 600

linch 22 1000

2-3inch 32 , 1200

l-2inch 50 1500

1-4 inch 100 16 00

l-8inch 135 2500

Wenham's Eeflex Illuminator 10 00

(The Messrs. Spencer & Sons furnish a full line of goods desir-
able by the microscopist, such as solid eye pieces camera lucidas,
and accessories generally. Their former connection with the
Optical Company has been dissolved, and they now continue
business on their own account, as above stated, at Geneva, N. Y.)

MICROSCOPES AND OBJECTIVES, BY R. B. TOLLES,
BOSTON, MASS.

Tolles' Large Microscope, •' B," no objectives $225 00

Student's stand, 1 inch E. P., 1, and l-4th inch object-
ives, packed in black walnut case 50 00

Additions, etc., to the above-
Extra eye pieces, each 4 00

Camera lucida 5 00

Sub- stage, for accessory apparatus 5 00

Sliding stage, giving horizontal and vertical movements

by hand 15 00

.Fine adjustment by lever and micrometer screw 20 00

Rack a.nd pinion for coarse adj ustment 12 00

Draw tube 4 00

Plain mirror • • • • 3 00

Thin glass stage to rotate on the optical axis 10 00

Packing boxes for transportation, extra 1 00

APPENDIX. 355

Student's Microscope, with one inch and one -fourth
inch objectives (second quality) one ocular, rack and
pinion, lever, fine adjustment for focus, sub-stage for
Illuminating apparatus, revolving diaphragm, plain
and concave mirrors, side stand for illuminating

opaque objects, black walnut case 90 00

TOLLES' FIRST CLASS OBJECTIVES.

Size Degrees. Price.

1-2 inch, Angle apertured 60 to 90 $40 00

4-10 " 90 to 120 4500

4-10 " ik ....135toH5 6500

1-4 or 1-5 " " .... 120 to 130 4500

1-4 " •• 150 55 00

1-4 •• '• 180 70 00

1-6 '• lk 180 75 00

1-S " » .... 180 80 00

1-10 " " .... 180 85 00

TOLLES' PATENT SOLID EYE PIECES.

l-2inch,"D" $800

1-4 inch 8 00

Either of the above, for his Student's Microscope 6 00

Wenham's Reflex Illuminator 1000

MICEOSCOPE STANDS, BY JOSEPH ZENTMAYER, 147

SOUTH FOURTH STREET, PHILADELPHIA, PA.

American Centennial Stand, binocular, with 5 eyepieces $300 00

Same, but monocular, 3 eye pieces 250 00

Concentric adjustable stage, extra 20 00

Best mahogany case, with fine handle and side case — 30 00
American Histological Stand, with plain and concave
mirrors attached to swinging radial bar, carrying, also,
sub-stage and diaphragms having three apertures, 1 (B)

eye piece, no case 30 00

Extra eye pieces, each 5 00

NOTE. — The following extras can be obtained of Mr.
Zentmayer at the prices below given. They are fur-

356 HOW TO SEE WITH THE MICROSCOPE.

nished at the suggestion of the author, who invariably
orders them for his friends and pupils. The instru-
ment is thus rendered efficient for all the ordinary pur-
poses of the working microscopist :

Supplemental revolving stage $1 00

Sub-stage adapter, to carry condenser, society screw 1 00

Eye-piece adapters, ready to carry solid cells, each 1 00

STAGE MICROMETERS, TEST PLATES, ETC., BY W.
A. ROGERS, CAMBRIDGE MASS.

Mr. Rogers has just completed his new machine, in the con-
struction of which several important improvements have been
secured. "We cheerfully add. our endorsement as to the regu-
larity and delicacy of his rulings. One of his plates, ruled up to
120,000 lines to the inch, now in our possession, is a marvel of art.
Owing to the extreme shallowness of Mr. Rogers' finer rulings,
they are more difficult tests than similar bands by Nobert. Mr.
Rogers furnishes a great variety of work. Some of his regular
plates may be thus described :

Stage Micrometer, consisting of 10 lines, 100, and 10
lines, 1,000 to the inch $125

Stage Micrometer, consisting of 25 lines, 200 to the inch,
10 lines, 1,000, 10 lines, 2,000, 10 lines, 4,000, 10 lines,
5,000, 10 lines, 10,000, 10 lines, 20,000, and 10 lines, 30,000
to the inch : 4 00

Stage Micrometers, ruled 1,000, 10,000,20,000, 30,000, 40,000
and 50,000 to the inch 500

Same as above, to 60,000 600

" to 70 ,000, $7.00; to 80 ,000, $8 .CO; to 90,000 900

kt " to 100,000 1000

(Closer rulings by special contract.)

Standard half-inches, with 50 subdivisions of l-100th inch
and 10 subdivisions in the centre of l-100th inch : 3 00

Standard centimeters, with 100 subdivisions 4 00

(At double the above prices Mr. Rogers furnishes a
complete discussion of the errors of the plates, and a

APPENDIX. 357

table showing the corrections to be applied to each
ruled space to reduce it to the United States standard.)

Standard half metres and standard metres, either on

glass, steel, iron or nickel surface, from $25.00 to 100 00

Test plates, micrometers, etc., are also ruled by Mr. Charles
Fasoldt, 594 Broadway, Troy, N". Y. The author has one of Mr
Fasoldt's 120,000 band plates, which he values very highly. He
regrets not being able to give M.r. Fasoldt's Catalog ;ie of Prices.

SUPPLEMENT.

CONTRIBUTION'S TO THE CINCINNATI MEDICAL NEWS.

Inasmuch as the author's contributions during the past six
years to the pages of the Cincinnati Medical News, and also the
American Journal of Microscopy contain instructions more or
less interesting to those commencing the study of the micro-
scope, it is thought desirable to present them in this supplement.
It was however found on inquiry that the back numbers ot the
Cincinnati journal were not to be obtained.

Dr. Blackham, of Dunkirk, N. Y., kindly placed his bound
volumes of the News in the hands of the writer, thus enabling
him to give the reader the following references, dates, etc., to
the several articles contained in the Medical News.

1875. January, " Microscope Objectives," p. 41 ; February

" Measurements of Holler Probbe Plate," p. 92; March
"Wide vs. Low Angled Objectives," p. 129.; April'
41 Diagnosis of Blood Stains, Dr. Woodward us. Dr!
Richardson," p. 177.; April, " A Simple Method of
Demonstrating Ang. Aperture," p. 183.; May, "• Wide
vs. Low Angled Objectives," p. 228.; June, " Dr. Ches-
ter Morris' Reports on Objectives," p. 281.; November,
" Wide vs. Low Angled Objectives," p. .515.

1876. January, "' Battle of the Object-Glasses," p. 41.; Febru-

ary, " The Mic. and Its Mis-iriterpretatuions," p. 86.;
March, " A New Microscope Stage," p. 232.; April,
"Robert's 19th Band," p. 287.; July, " Wythe's Ampli-
fiers," p. 433.; August, " Prof. J. E. Smith us. the
Nachet l-5th," p. 485.; August, " Trichiniasis," p. 488.
October, " Necessary Manipulation of the Microscope;
to Exhibit Fine Striae," p. 533.; December, " Torula
Cerevissein Human Urine," p. 677.

358

SUPPLEMENT. 359

1877. January, " Wenham's Reflex Illuminator," p. 74.;

" R. Hitchcock, Esq., vs. High Angles," p. 504.
The past contributions to the American Journal of Microscopy
will, owing to the kindness of Prof. Phin be given in full.

PROF. R. HITCHCOCK VS. HIGH ANGLES.

In the May number of the American Journal of Microscopy ,
I find an article containing a good-natured criticism of a paper
read by me before the Dunkirk Microscopical Society last
October.

Mr. Hitchcock candidly states that he has only seen a short
abstract of this paper, and has but an imperfect knowledge of
it. He further suggests that his main object was to call further
attention to my views, and he suggests that I put them in form,
so as to be published iu the American Journal.

For the benefit of Mr. Hitchcock, I will state, that my views
have been clearly stated in a series of articles, which have been
published in the Cincinnati Medical News during the past three
years, under the caption of "High us. Low Angles," and have
thence been quoted from and reprinted in various publications ;
certainly I cannot be expected to go over the ground anew at
this late day. It is true that I exhibited before the Dunkirk
Microscopical Society the No. 20 of the balsam Moller probe
platte, and also the 19th Nobert band, both so plainly that all
who were present saw without difficulty. These tests were not
difficult for the glasses employed, as was attested by the fact
that they were shown in a crowded room, amid the attendant
jars and vibrations, my object being to demonstrate the facility
with which my Tolles' duplex glasses handled these so-called
difficult tests.

To show the work of these same lenses by central light, I
selected the same test,iVay. Angulatum which the biological
committee at Philadelphia has declared impossible to be shown
at a less angle than 20 degrees from axis, with any medium
power glass. This test was displayed illuminated by light
through a central aperture placed close to the object, just large
enough to light the field, the diameter of the aperture being

360 HOW TO SEE WITH THE MICROSCOPE.

about 1-200 of an inch, direct light being used, i, e., without
mirror or condenser. The ease with which the duplex handled
this test was made amusing and apparent by my picking up the
stand, walking around the room, sitting it down again hap-
hazard before the lamp, when the resolution was found by a
gentleman appointed to examine to be unimpaired. This was
repeated three times. Will Mr. Hitchcock repeat, using a low
angle glass, be it a one-fifth or a one-fiftieth, and report?

I had other tests for central light work, including histological
and pathological preparations. It was impossible to show all
of these to so many people as were present, as it was, the entire
evening after the reading]of my paper was occupied. Hence, it
will be seen that I fought the low angles on their own chosen
ground, and with the express view of demonstrating that the
very best preforniance of the duplex lenses is seen by central
light,

Mr. Hitchcock further says that " the universal testimony of
our best authorities, who have spent their lives in microscopical
work, is against Prof Smith."

It was just this kind of testimony that affirmed a few years ago,
the highest possible aperture of an object glass to be 135 degrees;
that the resolution of the Nobert 19th band was a matter of
faith rather than of sight, etc., etc. Mr. Hitchcock is welcome
to the witnesses.

Note this fact, to- wit, in original investigations, the advanced
worker must necessarily be in a minority. I rejoice that some of
Mr. Hitchcock's witnesses have lately found cause to change
their opinions. Dr. Carpenter will no longer assert that the
resolutions of the Nobert 19th band is a " matter of faith, rather
than of sight." On the other hand, he has given unqualified
endorsement to the superiority of the duplex glasses.

Mr. Hitchcock desires to ask why I think that most of the work
in histology and pathology already " done" with the so-called
" working lenses" of narrow angles would require further atten-
tion, and with wide angled glasses I reply, that in the past four
years great advances have been made in the construction of
objectives, and in the manipulation of the microscope ; what
was considered a k' good working glass" ten years ago, would

\

SUPPLEMENT. 361

now be totally valueless for advanced work. We now demand,
as near as may be, perfect lenses, and superior dexterity in
handling them ; and these two conditions are inseparable. The
finer the objective the louder the call for expert manipulations.
That well-known term, u working lenses of narrow angles"
means, when stripped stark naked, easy going lenses, with no
screw collar to bother ; good working lenses, that a child or
sleepy adult without experience can use right along, will work
through covers of common window glass, big working distance,
and all that, etc., etc. Such are admirably adapted to the use of
those who use the microscope as a plaything ; admirable things,
too, to prove that " a little knowledge is a dangero.is thing."

Be it known, that I do not condemn an objective simply
because it has a narrow aperture ; conversely, I do not endorse
a glass on account of its wide angle. I have seen scores of
wide angle glasses not worth the cost of their brass mountings.
As to *4 errors in interpretation," the more perfect the lens, and
the more expert the manipulator, the less chance of error.*
Under high amplifications, a superior wide-angled glass, properly
handled, will generally prove the more reliable ; ami in advanced
work cannot be dispensed with, be the illumination central or
oblique.

Finally, I have to thank Mr. Hitchcock for his friendly criti-
cism. He seems, evidently, to be after the facts. I have re-
sponded to his request as well as I could with my limited time
and space. Two hours "over the tube" would demonstrate
more than volumes of print.

,T. EDWARDS SMITH.

Note.— On my last visit to the Dunkirk Society, May, 1877, 1
showed, I believe, for the first time, the Robert 19th band as an
opaque object, with my Tolles' one-tenth duplex, Beck's vertical
illuminator being used. It is obvious that the pencils of light
traversing that band were at least centrally disposed. J. E. S.

ANGULAR APERTURE AND CENTRAL ILLUMINATION.

In my reply to Prof. B. Hitchcock, reprinted in the August
number of this journal, I endeavored to respond to his court-

362 HOW TO SEE WITH THE MICROSCOPE.

eous request. My position had been placed fairly before the
public for years, and I was. for the nonce, content in maintain-
ing silence, feeling assured that when attention should be
thoroughly aroused as to the claims of high-angled glasses, that
I would be better understood. I think I can to-day safely
assert that my expectations have been realized, and to a greater
extent than I had any reason to anticipate.

Prof. Hitchcock has done me the honor of an extended reply
in the September number of this journal. It is noticeable that
he still preserves the same courteous bearing which character-
ized his previous paper ; indeed he pays me a compliment (uWe
have his plain statements, and we accept," etc., p. 110). All
this, as an index of his good nature, is very acceptable.

Nevertheless, be it remembered that it has been no part of my
purpose to obtain acceptance per se of my positions. On the
contrary it has been my earnest endeavor to excite attention,,
and to induce my readers to experiment for themselves. Hence
the results of my tedious and protracted experience with the
duplex lenses were printed in forcible terms (heterodox; as they
must have seemed to many), allowing no loop-hole for retraction
or qualification on my part. Hence it was, too, that I requested
Prof. Hitchcock to repeat some of my experiments ; Prof. H.
is compelled to decline, because he has not the objectives at
command. This I sincerely regret.

Premising that my time is fully occupied, and that it will be
impossible to reply directly to Piof. Hitchcock's last, and inter-
esting paper, I proceed to offer a few thoughts suggested by Uie
same.

First, what, in common parlance, constitutes a high-angled
objective V I think I understand Prof. Hitchcock— perhaps-
Tiot— let us see. It may be that in arriving at a mutual under-
standing on this point, we may get, generally, nearer coinci-
dence. Now, most observers associate with the term " high-
angled objectives," some great display of figures. Thus, 175°,
178C, or the " impossible " 180°. Others might go still further,
turning the 180° corner, and thus revel in the balsam angles,
say, up to 100° or higher. Such are not exactly my own notions.

I regard as high-angled, all objectives from a 4-inch to a

SUPPLEMENT. 363

l-75th, having respectively the highest possible attainable aper-
ture. It' this definition be accepted, then it occurs that what
was known as a high-angled l-10th of 130° ten years ago, would
now be classed as a medium-angled glass, and further, that an
inch objective of 45° would take rank as a high-angled glass,
and to the latter class of objectives do I refer as giving me the
best results for any and all work, selecting from this class of
objectives the one best adapted for the work in hand. Let me
illustrate by selecting a case that I almost daily have in practice
— to-wit :

Suppose, for instance, I am making preparations, say, of
malignant growths (notice that this is not a diatom), it would
doubtless be desirable tirst to make a preliminary examination.
I should, from the high-angled class of objectives, select the
above named inch of 45°. Why ?

First, because it has large working distance, which is not
disturbed by high eye-piecing. I am also enabled to bring the
mirror above the stage, and thus easily condense light on the
object ; and further, the working distance is so large that little
changes in the same do not disturb the object to such an object-
ionable extent as would occur had a higher power been selected.

Second, because this inch will show me structure up to 30,-
000 lines to the inch. It will not only bear the l-4th solid eye-
piece, but will give with it added force of definition, with
increased amplification.

Third, (result of first and second), because of all glasses I
have ever handled, I can get the most work (I have in bund)
out of it. For instance, its large reach, due to its working dis-
tance (the so-called penetration), enables me to focus through
the different planes of the object, while the entire specimen
remains fairly in view. 1 am further enabled to search through
my mount, with the least danger of allowing important struc-
tural elements to escape my attention— an important item.

Now, should such preliminary examination suggest the pres-
ence of structure calling for an objective capable of recognizing
lines 100.000 to the inch ; the inch of 45Q would be removed, and
a l-6th, having the widest aperture known, and working dis-
tance of one-fiftieth of an inch, substituted. With this supe-

3134 HOW TO SEE WITH THE MICROSCOPE.

rior defining glass I have still working distance enough to
illuminate my object by condensing sunlight on top of the
cover, thus securing exquisite definition under amplification of
more than 5,000 diameters. Here, again, with said l-6th, I get
better work than I can with any other style of glass.

Again, should it be desirable to cross-question my specimen
still closer, it would become necessary to remove the l-6th and
substitute a bran-new l-10th not yet a month old, the master-
piece of a young American optician. This l-10th has also the
widest aperture known, combining still more exquisite defini-
tion with sufficient working distance to allow the use of sun-
light as above named, while its glorious performances by central
light eclipse, yea, distance the work of any low-angled glass
extant, this beyond the ghost of a doubt. (And right here I
beg Prof. Hitchcock to be lenient, and to allow me a little mar-
gin ; it's hard to keep cool over the central-light performance of
this new MOth). But, with the employment of this l-10th, we
get into tolerably close quarters, the " difficulty of working " is
•enhanced. It won't do to put the screw-collar somewhere
between " zero " and somewhere else. And then, too, there has
got to be a good deal of that -w handling " attended to that
Prof. H. says will do so well to talk about before an audience.
Prof. Hitchcock here applies the great American question, and
asks if all this bother will pay. I reply, " Yea, verily !"

I shall be very grateful if Prof. Hitchcock will point me to
glasses that will take the place of those above mentioned. It
has so happened that those who have thus far undertaken this
task (and some have traveled hundreds of miles to accomplish
it) have resigned their previous ideas in my favor. In fact, I
have scores of friends made in just this kind of a way, and I
hope to add Prof. H. to the list.

Having thus given my ideas as to the nature and performance
of high-angled objectives, I beg to add that I see no necessity
for backing down from my original statements, although chal-
lenged by Prof. H. On the contrary, the advent of the new l-10th
serves to clinch the nail that I had previously well-driven home
with the duplex. And I now place again on record my deep-

SUPPLEMENT. 365

seated convictions that the use of such lenses as I have de-
scribed will be of the greatest use in histological observations.

Prof. Hitchcock's remarkable statement that *' much of the
very, best class of work is being done with second-class lenses,"
is, I fear, a slip of the pen. I, for one, certainly cannot agree
with him, even if so be, that I am found in a " minority.'7

Prof. Hitchcock has, I fear, found out my weak side, and
punches me sorely with Helmholtz's formulas. He has got
things nicely tabulated, to show at a glance just what can be
done and what can't. ISTow, I own up that of all the annoying
things on this mundane sphere (to me), these confounded tables
take the lead. Years after others as well as myself, saw the
19th Nobert band as clearly as we saw anything, came the
tables to prove that the thing was an utter impossibility !
It was noticeable too that, year after year, the tables got
changed, in fact, improved, to approximate more closely to the
facts. Verb. sap.

Again, Mr. Hitchcock informs us that "to attain the best
possible results from an objective, the angle of the illuminating
pencil must be the same as the angular aperture of the objec-
tive." This, he says, is the u chosen ground " for any lens.

To put it mildly, this is another most remarkable statement.
I dismiss it with the remark that my own experience teaches
me that such manipulation would defeat ninety low angled
glasses out of the hundred. He also, referring to my exhibition
of the 19th ]STobert band, with the vertical illuminator, sug-
gests the employment of a diaphragm to the back lens, pre-
dicting that the resolution would " doubtless be greatly
improved." I had already tried the experiment (and scores of
others); the result was nil.

Prof. Hitchcock further says that " Prof. Smith has not
taught us anything new about objectives." Well, doubtless a
little setting back of this kind will be of benefit to me, and
may prevent the growth of undue conceit. I confess, that I
really did entertain the notion that some of my " shows " before
the Dunkirk Microscopical Society were novel. For instance,
the exhibition of the Nobert 19th band as an opaque object ;
ditto, the showing of 30,000 lines to the inch with an inch
objective, and under an amplification of 740 diameters, etc.

366 HOW TO SEE WITH THE MICROSCOPE.

It was my intention to pass over one or two points presented
by Prof. Hitchcock, but fearing that silence may be miscon-
strued, a word or two may not be amiss. Prof. Hitchcock does
not deny that Dr. Carpenter has lately (note that point) given
bis unqualified endorsement to the superiority of the duplex
glasses, but he adds, " so does everybody else." This, too, must
be another slip of the pen, for it is all, yea, more than I have
claimed, for at the date of my Dunkirk lecture, the claims of
the duplex were not admitted by everybody. During the past
four years I have, myself, received hundreds of letters from as
many sceptics.

Prof. Hitchcock states that he was taken "a little by surprise"
by my claim that the " very best work of the duplex is seen by
central light," and with singular tact allows the little fact to
remain intact. This is too bad, for right here I expected the
thickest of the fight. It was, in fact, a my chosen ground."
Prof. II. is too much for me on tactics.

In this connection, I beg the reader to bear in mind that
while Prof. II. admitted the superiority of wide angles for the
resolution of " diatoms and Robert's test-plates," he neverthe-
less held that this did not support my view that high angles are
" universally preferable," (see this journal, May, 1877). To
meet this point, I stated in my response (this journal, August,
1877,) that I had not omitted such tests as are generally consid-
ered u chosen ground " for small apertures, i. e., what is gener-
ally understood and accepted as dead central illumination ; and
further, that among other • tests I selected Navicula angulata
illuminated by central light, because such resolution had been
publicly declared impossible. In reply Prof. II. kindly admits,
and in complimentary terms, all that I had claimed- as to cen-
tral light work, and he frankly adds, " they are just what we
would naturally expect a priori" Having made this full admis-
sion, Prof. H. seems to repent a little, and reverts to the sub-
ject again (page 112), still yielding that the high angles are
superior, both with oblique or central illumination, but for reso-
lutions only, because he says, the low angles have the greater
penetration. The nature of this, his residual error, is mani-
festly indicated in the piesent paper. Less than lt two hours

SUPPLEMENT. 367

over the tube " would convince Prof. Hitchcock that u the very
best performance (penetration, depth of focus, reach, or what
not included) is seen by central light. I again invite investi-
gation. The passage from Frey was original with Dr. Carpen-
ter ten years ago. I have no objection to urge.

A word, and let it bo with due respect to Dr. Carpenter. His
advanced age and failing eyesight, together with his many
duties and cares, forbid that he should continue to be the
authority he has been in the past. Singularly enough, the
doctrines advanced by Dr. Carpenter twelve years ago are still
endorsed by many to-day. This operates as a brake to the
wheel of progress ; surely Dr. C. is not to blame. Mr. Hitch-
cock asks if Dr. C. has changed his opinion since the fifth edi-
tion of his work ; in reply, I can say that the latest information
I have bearing on this point is this; about eighteen months
since a friend of mine was in London attending medical lect-
ures. He sought Dr. Carpenter's advice as to objectives ; Dr.
•C. advised him 10 go home and purchase the duplex, and my
friend did so purchase. Be all this as it may, while I enter-
tain the highest respect and admiration for his medical and
scientific attainments— his life of unceasing toil in his profes-
sion—I cannot, and for the reasons presented, attach impor-
tance to Dr. Carpenter's endorsement of the duplex glasses.
In other words, I should prefer the testimony of American
experts.

To resume, Mr. Hitchcock further says that " two hours over
the tube " has demonstrated something, he don't say exactly
what. At anyrate he volunteers his thanks, which I joyfully
accept. I should have said that " two hours jointly over the
tube " would demonstrate more than volumes of print. 1 hope
yet to enjoy such a tete-a-tete with friend Hitchcock, and prom-
ise in advance to delight him with the new wide-angled l-10th
before referred to. The new glass, too, confirms in a truly
practical manner the positions I have heretofore taken in print.

In conclusion, I have again to thank Prof. Hitchcock for his
good natured review of my previous article, and hope that he
will find nothing in this hastily written article objectionable.

368 HOW TO SEE WITH THE MICROSCOPE.

A FEW WORDS COtfCEUNING THE PERFORMANCE OF OBJEC-
TIVES.

Ed. Am. Jour. Microscopy— Referring to the letters of Mr. E.
Gundlach, printed in the August issue of the Cincinnati Medi-
cal News, it was noticed that Mr. Gundlach bases his optical
laws on the performance of his own objectives, or at least he
appeals confidently to his objectives to sustain his positions, as
to working distance, resolution and angular aperture.

Mr. Gundlach certainly has the right to state the principles
which govern him in the construction of object-glasse:, audit
would be well if other makers would follow his example. But
his readers must keep constantly in mind that while the general
principles he sets forth may not, as a rule, differ materially from
those actuating other opticans, each and every one has a
handling characteristically his own, and that ? necessary result
of his will be recognized in the characteristic performance of
various so-called first-class objectives ; and further, that between
the extremes comprised in the " handling" above named, a large
margin obtains, sufficient to warrant the acceptance of one ob-
jective to the exclusion of another.

The potency of these considerations is enhanced when we
remember that the slightest superiority in an objective is of the
highest importance. Beale says (kl> How to Work with the
Microscope," p. 285) " It is certain that the slightest advantage
in defining power ought not to 'be underrated. * * Im-
provement in the means of observation is of the utmost im-
portance, and however slight, always leads to the discovery of
new facts."

Again Dr. Beale writes (p. 283) •' The best object-glasses will
define clearly and accurately bodies which, from their trans-
parency, are quite invisible under objectives only slightly in-
ferior to the first."

It therefore becomes apparent that these little differences,
perhaps due to "handling" on the part of the optician, while
they are invaluable to the working microscopist, may also be
referable to the genius of the optician— to a particular method
of "handling" known optical laws.

SUPPLEMENT. 36 i)

By way of illustrating these "little differences," it may be
mentioned that among first-class objectives of the same mag-
nification, aperture and resolving power, greater and lesser
working distance will be found, and right here is the solution
of the dogma of (so-called) penetration, for, of the glasses above
mentioned, that one having the greater working distance will
be endowed with the greater penetration. This is the whole
thing in a nutshell, as set forth by the writer years ago.

If, in the comparison of two objectives, alike in magnification,
aperture and resolving power, one shall be found to have the
longer working distance, then is its superiority demonstrated,
and, be it remembered, that comparisons of objectives ought
always to be made in this kind of a way, otherwise any attempt
at comparison would be as futile as if we were to compare a tur-
nip with an orange.

Again, ij it can be shown that a medium power glass, say a
l-6th or a 1-1 Oth having the widest aperture known, and also com-
paratively large working distance, say l-50th of an inch, will
more than do any work that can be done with objectives of ex-
ceedingly high power, and correspondingly short working dis-
tance (excess of aperture being barred by the above named
conditions), it will be obvious that the former will be eminently
the superior glass.

Now the facts warrant the assertion that just such one-sixth
and one-tenth are made, and by American opticians. The
writer has had, and still has in his possession just such glasses.
His first contribution to the columns of the News, four years
since, set forth their claims, and he has never had occasion to
make either modification or retraction of his original statement.
When such occasion shall occur, the readers of this journal will
be promptly advised ; until then I claim (especially for the orie-
sixth) unequaled intensity of definition, widest known aperture,
combined with large working distance— in other words, without
that sacrifice of " working distance" alluded to by Mr.
Gundlach.

I embrace this, my first opportunity, to say that I have lately
examined at length a new duplex one-tenth, the work of a
young American optician. This new one-tenth is similar in

24 Microscopy.

370 HOW TO SEE WITH THE MICROSCOPE.

aperture and has greater working distance than my own one-
tenth ; its work over such tests as the Nobert and Moller (balsam)
plates was quite equal to that of its formidable competitor,
while the views it gave by central light were simply glorious,
excelling the old one-tenth. This, as a first attempt on the part
cf a young optician, is truly encouraging. These new duplex
glasses will receive my earnest attention, and I may have, in the
future, something more to say about them.

Allow me to further state, that, being desirous of acquainting
myself with the work of our own opticians, I wrote to the
Rochester firm, asking the loan of objectives for examination
and study. They responded promptly, sending me by return mail
a full line of Mr. Gundlach's lowest priced "Student's'' work.
They certainly had no time to select exceptional glasses. My
time has been so thoroughly occupied, I have not yet given them
the attention they deserve, but as far as they have been examined
J am much pleased with them— a three-fourth inch at $6, a one-
half inch at $8, and a three-tenths at $11, are very finejindeed
for their cost.

ANGULAR APERTURE ONCE MORE.

Ed. Am. Jour. Microscopy. — The discussion between Prof.
Hitchcock and myself, which, during the last few months you
have done us the honor to print, seems to have become some-
what of a rambling nature. Prof. Hitchcock " changes base "
so often, that it would bother a streak of lightning to catch —
much less corner him. Be this as it may— and perchance he
might return the compliment,! can only say that I have endeav-
ored to stick to the points at issue— the merits of high, as com-
pared with low angles, I have attempted to set forth from a
practical standpoint, being tolerably familiar with the use of
either style of glass.

I have tried my best to have Prof. Hitchcock examine high-
angled glasses for himself, and report results, but, as your read-
ers are aware, from his own assertions, Prof. Hitchcock does
not claim a practical knowledge of them, and as a matter of
course he cannot see what that " handling " (of which it will do

SUPPLEMENT.

371

so well " to talk about before an audience ") amounts to. Of a
piece with this comes his statements that such and such posi-
tions of my own are '* not proved," and that before he accepts
them he " must know why."

I submit : that the only possible method of convincing Prof.
Hitchcock will be the practical one, in this instance, however,
quite impracticable, to-wit : " two (or more) hours conjointly
over the tube," or until he shall have done me the honor to
adopt my suggestion, and experiment with the high angles for
himself ; in the latter case, obviously, he ought not to expect
first-class results from the wide angles until at least he shall
have learned that something is due to " handling." I repeat
that until one or the other expedient is adopted, we might con-
tinue the present discussion until doomsday, and on my part
without a vistige of any chance of convincing Prof. Hitchcock.
I therefore offer the following brief remarks by way of closing
a controversy which, in the nature of things cannot lead to any
fixed results.

Prof. Hitchcock asks, " Why strain a one-inch to see 30,000
lines to an inch, with a deep eye-piece, when the half-inch
would do the same work without being pressed so hard V"

Well, let us strip things " stark naked," and find out u why."
First, with the inch I get better definition ; second, longer
working distance ; and, third, because the inch, with deep eye-
piecing " is not pressed so hard as the half-inch — and this is
my reply to Prof. Hitchcock. As a matter of course he will
come back at me with the stereotyped assertion, " I must know
why." He says, too, u Until his (my) experiments are published
and subjected to public examination they are not to be accept-
ed, etc." Well, by the laws, my experiments have been both
published and subjected to public examination. But, unfortu-
nately, Prof. H. wasn't there ! Note that.

Further, I now propose to put the inch and half-inch to a
practical test. Thus, let Prof. Rodgers, of Cambridge, rule a
band of 40,000 lines to the inch, and let Prof. Hitchcock count
them if he can with a low half-inch (say of 40°). I hazard the
prediction that he will fail, and furthermore, that I will be
enabled to count them with an inch of 45°. I am ready for such
test in any shape that Prof. Hitchcock may suggest.

372 HOW TO SEE WITH THE MICROSCOPE.

To get back to our " moutons." When I stated 30,000 as the
limit for definition of the inch, I held a good large margin (to
swear by) in reserve. This, as the 30,000 was u millions " as far
as establishing my point was concerned, now that the readers of
this 3ournal have got used to the >l SO " I will add that I have no
trouble in seeing the 40,000 band of a Bodger's test-plate, and
most beautifully ruled they are. Here is an added strain of ten
thousand on the inch, but it is as good as ever ! (One of these
days I must give your readers a description of an exquisitely
ruled plate, up to 80,000 to the inch, and by the same talented
artist.)

But to business. I have as fine a half-inch of 38Q as I have
ever seen, a glass selected with much care, having spent consid-
erable time in making the selection, so as to have the very best;
for, be it known, I sometimes (not often) have use for just this
sort of glass. Well, now, this half-inch has shorter working
distance, and, as a matter of course, less penetration than has
the inch of 45°, while the last-named inch of 45Q has much the
superior definition.

Now, I am perfectly acquainted with the tk points " of these
two objectives, and can make either put its u best foot fore-
most," (hence the " handling " may be counted out.) Both are
my own, and I can at will use ths one that I prefer. Which
would Prof. Hitchcock use under the same circumstances V Or,
leaving the Professor out, which would the reader select ?
Which glass would be " strained " the most ?

Prof. Hitchcock reminds his readers that he has " already ad-
mitted to Prof. Smith that Tolles and Spencer are making won-
derful glasses, etc." Yes, so he did, but he put a fence round
them ; thus he adds " but for resolutions only." When Prof.
Hitchcock shall become as well acquainted with the work of
Spencer and Tolles as are others, that fence will step down and
out. I accept no loop-hole, but stand to the position heretofore
assumed, to- wit, that the above named glasses are not equalled
for "• any and all*work," a« set forth in my last paper.

Now about Dr. Johnson's showing the 19th band as an opaque
object in the year 1872 or thereabouts. Here is a legitimate
chance to try on Prof. Hitchcock's conditions, to- wit: Were

SUPPLEMENT. 373

Dr. Johnson's experiments with the 19th band published V (as
were my own). Again, were they " subjected " to public exam-
ination ? " ( as were my own.) Let the Professor's rule
work both ways. Meanwhile I now assert, and know
whereof I affirm, that a Powell & Lealand l-10th of 1872
cannot be forced to show the 19th band by lamplight. In gen-
eral, I don't propose to accept anything done with the 19th band
five years ago, as comparable with what is being done in 1877.
Again, all who have seen the 19th band as displayed with the
duplex and modified Beck illuminator, instantly admit that for
wondrous delicacy of definition, the total absence of the "ghost"
of a diffraction line, all other methods of illumination (by arti-
ficial light) are simply " nowhere." And further, that any
attempt at photographing these wonderful lines has been but
approximative. To be more definite, the best photograph of the
19th band yet made is simply a caricature. Nevertheless it is
wonderful that Col. Woodward has succeeded as well as he ha.s,
and his photographs are the best that I have seen.

A word as to the mathematical tables. There can be no pos-
sible objection to these, when (it's my chance to say "when"
now) they agree with obvious facts ; they are objectionable when
they are not in accord with facts. I stand ready to accept truth
in any form ; ditto, to repel error. Now the facts are, that from
a mathematical standpoint the limits of vision have been
erroneously " set " again and again. I simply protest against
fighting facts with mathematics— simply this, and nothing more.

In drawing towards the close of this article, I desire, as apro-
pos to the question at issue, to state a little bit of personal expe-
rience, viz : About a year ago a gentleman, a professor occupy-
ing a responsible position, gave me a carte blanche to provide him
with a medium power lens. He was particular to state that he
was engaged in histological studies, and wanted the glass for
such and similar purposes. In response, he was furnished with
a l-6th duplex. Last summer he visited me during his vacation
and became my pupil. He was, of course, an apt scholar, and
quick to learn. He spent with me weeks in acquiring the man-
ipulations of this glass, and became quite expert. When he left
me he said, " I have now learned practically what was done for

374 HOW TO SEE WITH THE MICROSCOPE.

me in the selection of the objective, which I now prize more
than ever, and it is astonishing how much is due to handling. I
had no idea of it." A few weeks ago he wrote me that he was
doing finely with the duplex, and had succeeded with it in trac-
ing structure (histological) that could not possibly have been
seen with any low-angled glass. Further, that the very best
makes of the low angles were constantly within his reach.

Now it is a fact that before I furnished this gentleman with
the duplex, he was as fully committed in favor of low angles as
Prof. Hitchcock can be ; but, unlike Prof. H., he commenced
the study of high apertures, and with the sure results above
narrated. His address will be furnished to any one desiring it.

Prof. Hitchcock says something (I quote from memory) about
" accepting defeat in a becoming manner." I desire most earn-
estly to advertise the fact that it is not, has not, been any part
of my purpose to " defeat " Prof. Hitchcock, and as I have
understood the gentleman from the very onset, he is not, nor
has he been, in a position to suffer defeat. He simply wants
the facts, and I have endeavored to furnish them, and if so be
that any good has been brought about by this discussion, your
readers are quite as much indebted to Prof. Hitchcock as to any
one else.

In conclusion, I return Prof. Hitchcock my sincere thanks
for the courteous and gentlemanly consideration he has
ever extended me. It has been my intention to reciprocate, and
with the hope that I have been in a measure successfnl, and
with the kindest feelings towards Prof. Hitchcock, to you Mr.
Editor, and to your many readers, I remain sincerely yours,

J. EDWARDS SMITH.

NOTE.— In your October number, page 132, an obvious error
occurs. For u what was known as a high-angled l-10th of 180°
ten years ago," read " 130° ten years ago," etc. J. E. S.

SUPPLEMENT. 375

DISCTJRSORY THOUGHTS RELATING TO THE USB AND ABUSE
OF THE MICROSCOPE.

An Address delivered by Prof. J. Edwards Smith, before the Dunkirk
Microscopical Society, Tuesday Evening, October 31, 1876.

To the Members of the Dunkirk Microscopical Society :

GENTLEMEN:— About twelve months ago a friend of mine and
a brother microscopist, ordered from London a low-angled l-4th
inch objective ; my friend was engaged in histological investiga-
tions, and felt the need of a reliable medium-power glass. He
had been told that wide-angled glasses, although very suitable
for the purposes of the diatomist, were hardly suitable for the
work he had in hand ; he was told, too, that the thing needed
was a glass of low or moderate angle, say from 50° to 70°, and
one that had great working distance ; in short, as the saying
goes, he needed a good " working glass."

In due time the objective was received, and one very pleasant
evening my friend called on me expressly to show the work of
the lens. I remember that we had a very enjoyable time, amus-
ing ourselves by looking over a variety of specimens suitable
for the glass. In the course of the evening he exhibited a beau-
tiful section of a human tooth, and placing the same under the
l-4th, called my attention to the "Kasmyth's membrane,"
described by Frey and others.

This was a matter of interest to me, for I had heard much of
this " Nasmyth's membrane ;" I had examined human teeth
time and time again with my own wide-angled glasses, but had
never been able to discover the same. I was, in fact, somewhat
curious about the matter. It seemed odd, to say the least, that
my glasses, which would show me clearly and accurately, lines
as close as 120,000 to the English inch, should fail to show me
the existence of a membrane said to be about 1-6,000 of an inch
in thickness ; and then again I had hunted with a low-angled
l-4th of my own without success. Hence it was with expect-
ancy and interest that I put my eye to the tube ; I saw a
decided thickening of the margin of the crown of the tooth, and
was informed that this was the veritable " Nasmyth." But,

376 HOW TO SEE WITH THE MICROSCOPE.

said I, " is this thickened edge not the fault of the objective,
and suppose that we examine the specimen with another glass?"

Removing the London lens, I substituted a wide-angled l-6th
of plus 180° of aperture, and on adjusting carefully to the thick-
ness of covering glass, I soon had a splendid view of the pre-
paration, by far finer than that shown by the London glass ;
and as I had supposed would be the case, I n3w had a nice
clean edge in the place of the thickened one before mentioned.
The superiority of the definition over that of the l-4th was
apparent; and tht capacity of the 1 -6th to bear the 1 -4th inch
solid eye-piece and amplifier— thus carrying the amplification
up to nearly 4,000 diameters— was in a few moments demonstra-
ted, but the Nasmyth's membrane was not to be seen under any
amplification.

At this time it occurred to me that I might possibly make a
membrane as described by the books, and as shown by the Lon-
don lens. Turning the collar of the l-6th so as to throw the
glass considerably out of adjustment, and again focussing the
object, I was much amused to find that I had the identical
membrane, as shown by the imported glass, and also, that as
the collar was moved, the membrane could be made thick or
thin to suit !

The result of this little episode was simply this— my friend
now owns and uses on histological work an American made l-6th
of 180° of aperture.

I have related, as briefly as possible, this little incident, and
exactly as it occurred. I desire to say, however, that I do not
deny the existence of " Nasmyth's membrane," described in the
various works on physiology and histology. Nevertheless can-
dor compels me to state that I have in times past made diligent
search, and have failed to recognize a structure which is taught
even in our elementary school books, as if it were a common?-
place thing !

Months ago it occurred to me that the membrane referred to
might only be found on teeth of the first dentition, and obvi-
ously would be found wanting on the tooth of an adult. This
idea sent me to the dentist's oflice : such specimens were pro-
cured, but the " Xasmyth " still defeated my search therefor.

SUPPLEMENT. 377

Some months ago I was engaged in teaching microscopy in
one of our public schools. At that time I had the class in
physiology in hand, and it was my especial purpose to show
them actually, structures which were described and pictured in
the text book used. I had not proceeded far before we ran
against this " Nasmyth's membrane," and I was compelled to
state substantially the experience which I have now related to
you.

There is not a class of persons on earth less appreciated or
more poorly paid than those engaged in histological investiga-
tions, and for their indefatigable perseverance I entertain a
profound respect ; but it has often occurred to me that as a class
they have been content to work with very poor tools, and it is
safe to say that a great deal of the ground already studied will
have to be reinvestigated, and with better glasses— with a bet-
ter knowledge of those manipulations requisite to the use of
wide-angled lenses. Nor can the necessary manipulations be
acquired in the ordinary routine of investigation ; it is an art
of itself, and calls for special attention, requiring as much
study as the art of manipulating a pianoforte or an organ.

It is a very commonplace remark, that, for the purposes of the
histologist, low-angled glasses, of moderate definition, are the
best suited. And yet, if we consult their latest works, we will
nnd structures described that call for the best lenses of the
widest angles. Take, for instance, the muscle sheaths, or the
-axis cylinders of the nerves described by Frey, in his last
•edition. Coming down to commonplace things, I affirm that
the simple trachea of a bee cannot be studied with advantage
with other than lenses of the widest angles.

There is perhaps no microscopic object more common than
these tracheaes. They are to be found mounted in the cabinet
of every microscopist, and we have all of us read about them
in the books ; we have examined them again and again, times
without number, with objectives ranging from the inch to
the l-5th, or perhaps to the l-10th. Now I ask you take a look
at them on my account, and if possible inform me how these
tracheal coils terminate : what is the structure at their very last
end? What is the least diameter of these terminal coils ? Here

378 HOW TO SEE WITH THE MICROSCOPE.

you have a problem in hand, to which, for exquisite intensity of
definition, or nicety of manipulation, the resolution of the
Moller or Nobert plates are child's-play matters ! And if you
should be desirous of testing your lenses as to their capacity for
histological work, the trachea will be found to be one of the
very best test objects in existence, and will surely furnish you
valuable ideas as to the relative value of wide and low angled
glasses for the purposes of histological research.

Not long since one of our most skilful physicians sent me a
sample of urine from a child supposed to be suffering from a
disease of the kidneys. Jt was a perplexing case, and the med-
ical gentleman in charge hoped that the microscope would give
some light on the case ; when examined with a low power l-5th
of 70Q aperture, the specimen appeared in every respect
healthy ; but on further examination with a wide-angled glass*
and with an amplification of nearly 4,000 diameters, it was-
found to be literally swarming with vibriones. There were bil-
lions upon billions' of them in every field examined, all of which
were totally invisible to the low-angled l-5th.

We often hear the remark, that wide-angled glasses are just
the thing for the display of lined objects, surface markings,,
diatoms, etc., but that owing to their short focal length, and
limited working distance— the trouble Attending the adjustment
of collar— and in general, the difficulties pertaining to their use,
that they are unsuited to the purposes of the histologist ; while
on the contrary, low-angled glasses of greater working distance
requiring no skill in management, are the tools with which the
real work of the microscope has been, and will continue to be
done, and such are fondly termed good, honest and reliable
'• working glasses."

1 can never listen to this line of argument without entertain-
ing the suspicion that sloth and inactivity lay at the bottom. We-
never hear astronomers complain of the care they are compelled
to use in instrumentation ; on the contrary, they pride them-
selves on the accomplishment of being able to work instrument*
requiring a great amount of skill and precision in manipula-
tion.

The objection of short working distance originated years ago.

SUPPLEMENT. 379

when German pathologists were in the habit 'of using common
window glass to cover their mounts, and at that time the
extremely thin glass, now so easily obtainable, was unknown.
All this is now changed ; the widest angled lenses known giving
all desirable amplification, will admit the use of covers l-50th
of an inch thick, while covering glass measuring .003 can easily
be procured.

A vast amount of work has been done with these k' honest
and reliable working glasses," and, as I have before said, will
have to be done over again, and this revisory work is now in
progress. But while there is some excuse for the investigators
of the past, who used the best instruments then obtainable,
what shall we say of those of to-day who persistently refuse to
avail themselves of the wonderful progress the optician is able
to demonstrate in this centennial year ?

I have advanced the idea that working pathologists were too
often content to work with poor tools. I made that remark in
good faith, and believe tnat it will be found to be trne. Never-
theless the pathologists of the past, or even of the present dayr
are by no means wholly at fault, when we remember that the
entire corps .of observers to whom we are indebted for all that
has been taught through the aid of the microscope, were men
who were regularly engaged in the respective duties of their
several professions, and that most of them have tilled profes-
sional chairs in various institutions of learning. These men, in
studying the use of the microscope, each and every one of them
were compelled to dig and trench for themselves; the instru-
ment which to them was as all-important as the compass to the
navigator, was far, very far, from being as true and reliable a*
" the needle to the pole." Once launched on the unknown, but
to them, fascinating sea of scientific investigation, every spare
moment that could be snatched from their regular engagements
was devoted to its exploration. It was a tiny sea, within a
microcosm, replete with interest, and capable, as if by the touch
of the optician's wand, of boundless expansion I

These self-abnegating, self-sacrificing men fully accomplished
their task. It was a labor of love, and the results they obtained
were given to the world without money and without price.

380 HOW TO SEE WITH THE MICROSCOPE.

Among the investigators of our own day, 1 will refer you to
one whose untiring industry has earned for him a world-wide
reputation. I allude to Dr. Lionel S. Beale, F. R. S. Dr.
Beale, as you are aware, has been contemporary with, and the
supporter of, Dr. Carpenter's heretofore universally received
opinions as to the relative capacity of wide and low angled
objectives. Dr. Beale, in his work, " How to Work with the
Microscope,"— I quote from the third edition, page 7 — says as
follows : " For ordinary work it will be found inconvenient if
the object-glass when in focus comes too close to the object.
This is a defect in glasses having a high angle of aperture. * *
Olasses with a high angle of aperture admit much light, and
detine many structures of an exceedingly delicate nature, which
look confused when examined by ordinary powers. For general
work I recommend glasses with an angle of not more than 50Q
to 100Q

tk Mr. Ross has lately made glasses having an angle of 170°,
which are valuable for investigations upon very delicate and
thin structures, such as the diatomaceae ; but such powers are
not well adapted for ordinary work. The importance of
arranging the object very carefully, and the necessity of paying
great attention to the illumination, render these glasses incon-
venient for general observation. The penetrating power of
glasses with a low angle is much greater than in those of a high
angle of aperture, so that exact focussing is much more impor-
tant in the latter than in the former."

This, in its popular acceptation, is the square doctrine first
advanced by Dr. Carpenter, and it has suffered no loss by its
filtration through the mind of Dr. Beale. It is the doctrine
which has been generally received and accepted. It is the
dogma which ten years ago I thought ought not to be true, and
of wnich to-night I stand before you the prince of sceptics !

In the quotation which 1 have presented, there are two domi-
nant ideas ; the one displays the inconvenience attending the use
of wide-angled glasses, and to this objection I have already
paid my respects in due form ; the other presents the theory of
** penetration " as originally advanced by Dr. Carpenter, sup-

SUPPLEMENT. 381

ported by Dr. Beale, and generally endorsed by microscopists
of Europe and America.

I have not the time this evening, nor would I weary your
patience by the discussion of this dogma of penetration, any
further than to admit that it was true ten years ago, when first
announced by Dr. Carpenter, but can have no possible present
force in reference to the wide aperture glasses of to-day. I am
also quite prepared to grant that a spectacle lens of sixty inches
focus needs less skill in management than a duplex l-10th of
plus 180° of aperture !

After all, I get considerable comfort out of the quotation
already presented. Dr. Beale says, " that glasses with a high
angle of aperture admit much light, and define many structures
of an exceedingly delicate nature, which look confused when
examined by ordinary powers." Notice the wording ; he does
not say diatoms. He does say, u many structures of an exceed-
ingly delicate nature, which look confused when examined by
ordinary powers." It is a candid and manly admission, and I
honor his candor. It is the truth, the whole truth, and nothing
but the truth ; while for brevity of form, or clearness of expres-
sion, these half dozen words leave nothing to be desired beyond
what is here so forcibly stated ; and I beg of you not to lose
sight of the fact that if this was true of wide- angled glasses
made in 1865, it is equally so of those of 1876.

Another fact will bear to be borne in mind. It is this : when
Dr. Beale wrote in 1865, he was very far from being expert in
the use of wide apertures. I will read to you further from the
same paragraph: "In order to adjust the object-glass, it is
first arranged for an uncovered object ; then any object covered
with thin glass is brought into focus by moving the body of the
microscope ; next, the ring which carries the third lens is
screwed round until any particles of dust upon the upper sur-
face of the glass are brought into. focus. The glass is* then cor-
rected for examining the covered object which may be brought
into focus." It will be seen that the method of adjustment
adopted by Dr. Beale is precisely the same as that used by
many for measuring the thickness of covering glass, and when
the milled head of the fine adjustment is properly graduated, and

382 HOW TO SEE WITH THE MICROSCOPE.

the " run" of the fine adjustment is known, the plan is a con-
venient one, and will give measures tolerably correct ; but for
the purpose of adjusting an object-glass it is obviously fanlty,
and would in almost every instance defeat such wide angled
lenses as I am in the habit of using. Dr. Beale's instructions
nsjto the adjustment of wide-angled lenses must be taken "cum
grano salis," aud will indeed be more honored in the breach
than in the observance.

It is with pleasure that I now turn to page 217, and read as
follows : " Besides extreme minuteness in mere size, extreme
tenuity or transparancy may interfere with the definition of an
object. Now the greatest difference is observed in object-
glasses in this particular. The best object-glasses will define
clearly and accurately— mark the words," clearly and accurately"
— bodies which, from their transparency, are quite invisible
under objectives only slightly inferior to the first."

Now the question arises at once, Where shall we find these
best object-glasses, which define so clearly and so accurately
such delicate and transparent objects? Referring again to
page 7, Dr. Beale responds thus : " Glasses with a high angle
•of aperture admit much light, and define many objects of an
exceedingly delicate nature, which look confused when exam-
ined by ordinary powers."

The Doctor having thus squarely settled the question, most
kindly goes on to tell us where we can get these wide-angled
glasses, and I read right along, as before quoted : " Mr. Boss
has lately made glasses having an angle of 170°, which are valu-
able for investigations upon very many delicate and thin struc-
tures," etc., etc.

It is especially a part of my purpose in appearing before you
this evening to show you " clearly and accurately," and by the
aid of glasses of American manufacture, which for width of
aperture have never been excelled, some of these extremely thin
.and transparent objects, and thus prove to you the truth of Dr.
Beale's assertion ; and relying on the correctness of the old
adage that " seeing is believing," I can hardly fail in the
-demonstration of the accuracy of Dr. Beale's position.

Pardon a momentary digression, and allow me to turn to page

SUPPLEMENT. 383

216. Here I read : u If any one makes out new points of struc-
ture by any new method, all that such an authority who differs
lias to do is to state that he has not been able to see the struc-
ture described so and so. Authority too often denies the ex-
istence of what it has itself been unable to see. Many auth-
orities deny the existence of what they haye not seen, while
they have not taken the pains to try the only method of demon-
stration by which the appearances in question could be seen."

Now we perceive that the Doctor is in a complaining mood.
The root of the matter was simply this : Dr. Beale paid great
.attention to instrumentation : the first l-25th and the first l-50th
objectives in existence were made for him ; he was not very par-
ticular as to their angle, although it is noticeable that he
claimed for them " plenty of light." But the fact is indisput-
able that his instrumentation has been in advance of that of the
London microscopists. Dr. Beale was in fact in a position very
similar to those of the present day, who, conscious of the superi-
ority of their glasses, are disposed to regard the blind " authori-
ties " referred to as unworthy of special consideration.

I desire in this connection to call your attention to the history
of the diatom of which we have all of us heard so much about
during the past nine years. I refer to Amphipleura pellucida.
Who of us here cannot recall the time when the existence of
striae on this shell was stoutly denied V We can remember, too,
when Dr. Woodward settled this much vexed question by pro-
ducing his photographs displaying the strife on what he was
pleased to call " this well-marked diatom." And now that these
markings are no longer to be questioned, as exhibited on dry
mounts, and by the employment of monochromatic sunlight,
full eighty per cent, of our American observers fail to exhibit
*k this well-marked diatom" by lamp illumination, even wh«n
dry mounted. I have a balsam mount of this shell with me,
.and hope to show you the lines of No. 20 of the Moller plate
this evening before we part, and also the 19th band of the
Nobert test plate, and by the aid of American made lenses of
medium power.

Let me call your attention, for a few moments only, to another
subject. We often hear the diatomist spoken of in terms,

384 HOW TO SEE WITH THE MICROSCOPE.

almost, of contempt. They are too often regarded by the hist-
ologist as a class of observers who use the microscope as a mere
plaything ; and the fact that the diatomists are not altogether
agreed as to the structure of some of their favorite shells, is
often used as an argument to show the folly of studying the
diatomacese at all !

All this, my friends, is sheer sophistry. The study of the dia-
tomaceae is as legitimate as that of any other branch of the
science of biology, and the labors of the diatomists have not
been for naught ; it is to them, and to their constant demands
on the optician, that we are indebted for the wonderful
improvements which have been made in object-glasses; and I am
bold enough to tell you that skillful diatomists can tell you as-
much concerning the structure of a diatom, as can the patholo-
gist—equally skilled— inform you as to the structure of a blood
corpuscle !

But to the student, to those who desire to prepare themselves
for advanced work, the study of the diatomaceae cannot be neg-
lected. No line of practice has yet been discovered that will
teach the student the use and management of his tools, that
can at all compete with the superior claims of these minute org-
anisms. It is said that " adversity tries us and shows up our
best qualities." These little shells, too, will try the would-be-
manipulator, and, like the country judge, show up his worst
qualities.

It was not my purpose to enter at all into the details concern-
ing the use of objectives ; but it will perhaps be well not to let
the opportunity pass without alluding to the fact that a wide-
angled glass requires totally different management, in some
respects, from those of narrow apertures.

Those who have been accustomed to the use of the low angles
will, on a slight acquaintance with glasses possessing wide aper-
tures, almost invariably assert that the latter do not give as
good results, when worked by central, of centrally disposed
light, as they are accustomed to get from the former. A
moment or two devoted to the consideration of the situation,
will, I think, furnish the key thereto.

"When we use a narrow-angled objective, the oblique or lateral

SUPPLEMENT. 385

rays are per force excluded. The objective will not receive
them, and there can be no possible doubt but that such 'work is
being done with centrally disposed light, such as the observer
desires ; there is no special manipulation or management neces-
sary to secure this, for the objective will admit centrally dis-
posed rays, and none other.

But in the handling of a wide^angled lens the conditions are
essentially changed, and this change of condition involves in
turn a change of handling, and of management.

Hence it occurs, that in using a wide-angled glass by central
or centrally disposed light, some arrangement must be provided
for the purpose of shutting out the lateral rays ; these the glass
will admit, and in default of the provision referred to, will steal
in, cause interference, and defeat both observer and objective.
To shut out these lateral pencils would seem eminently the bus-
iness of the usual diaphragm box.

This provoking little piece of apparatus, this diaphragm box,
is supplied with almost every stand in use, and is as faulty in
operation as human ingenuity in construction could devise ; in
general these boxes are furnished with a shutter pierced with
openings of various sizes, and placed from one-half to one inch
below the object-carrier of the stage. Now, suppose we are
using a wide-angled lens, and being desirous of central light
only, we attempt the use of the smallest opening of the shutter.
What now is the result ?

It is as follows : the pencils of light enter the small aperture,
emerge and diverge within, and fill the box with simply light of
low intensity. It has now become a washed-out, wire-drawn
light, lacking force, and, I may say, velocity; the objective now
in turn receives this much- abused illumination, not only the
central pencils thereof, but lateral ones also ; and the working
angle used will be determined by the depth and diameter of the
diaphragm box.

A proper diaphragm for general use — not diaphragm box, for
the less of the box the better— is a plate pierced with a central
opening of about the size of a large needle, and so mounted as
to approach the iower edge of the mount closely as possible
without suffering actual contact. To construct this little piece

25 Microscopy.

386 HOW TO SEE WITH THE MICROSCOPE.

of apparatus will not make any very severe demands on your
mechanical skill.

Those of my hearers who read the London Monthly Micro-
scopical Journal will remember that the capacity to display the
markings of J^avicula angulata by central light, was considered
a feat only to be performed by low-angled glasses of superior
excellence. Some of you, too, may have read the report of a
certain biological committee who met in Philadelphia last year
for the purpose of testing the object-glasses of several makers ;
one of the tests used was the exhibition of the markings of this
same dry mounted Navicula angulata by central light.

I was simply astounded when I read the report, in public
print, of this biological* committee, and learned that in their
hands that Angulata had defeated a wide-angled American
l-10th, and I immediately repeated the experiment, using a
similar l-10th, by the s?me maker, and worked with a dia-
phragm plate perforated with an opening, say, l-200th of an inch
in diameter, and placed almost in contact with the under sur-
face of the mount. The result was amusing enough ! I instantly
had the markings " clearly and accurately " defined ; the prob-
lem was, indeed, to avoid seeing them ! In fact nothing short
of sheer intention, or, what is worse, bad manipulation, could
have defeated the objective. I then repeated the experiment,
using this time a balsam mounted Angulata— the No. 11 of the
Moller plate — and was almost instantly rewarded, as in the pre-
vious instance. I am prepared to again repeat this experiment
this evening should you so desire.

Again, the converse of what has been said is also true, namely
in working with a wide-angled objective, and with^oblique light,
it is important to shut out the central pencils. About a year
ago, I devised a simple little instrument, which gave access only
to a narrow wedge of oblique light, and thus gave added force
to the definition of the objective— and this " oblique dia-
phragm " was permanently fitted to the stage of my stand.

The most efficient instrument of this nature, however, is
" Wenham's reflex illuminator," an ingenious accessory, and so
contrived as to shut out all rays less than 41° interior, which, of
course, has emergence at 90° into air. The reflex illuminator,

SUPPLEMENT. 387

which was designed by its inventor to give a dark field,
becomes, when used on balsam mounts, with American object-
glasses, having balsam angles ranging in the nineties, not a
reflex, but a direct illuminator, and a most efficient aid to the
definition of the lens. By it I am enabled to show the trans-
verse striae of No. 20 of the Holier plate so clearly that any old
lady who can read her family bible could hardly fail of recog-
nizing the striae on "this well-marked diatom." I have the
instrument with me, and shall be happy to show you its work
on the Moller plate. *

It was mainly the purpose of these desultory remarks to call
your attention to the importance of instrumentation ; absolute
perfection has not been, and never will be obtained. There
never has been, nor will there ever be made, an instrument of
precision that does not embody inherently some radical weak-
ness, some dangerous fault. The practical astronomer is not
only early taught the nature and use of the various instruments
to be found in the observatory, and made acquainted with their
several imperfections, both optical and mechanical, but he is
compelled to acquaint himself thoroughly with the methods
employed to eliminate these imperfections. Having thus per-
force of his preliminary study acquired a thorough perception
of the Scylla and Charybdis which environ the use of instru-
ments, it becomes in turn a life's study to further remove exist-
ing difficulties, or to provide better and more competent means
of compensation therefor.

I have no doubt but that it would be interesting and instruc-
tive to detail some of the exquisitely precise methods employed
by the astronomer to detect and compensate for the unavoidable
errors of instrumentation, but time forbids. I will, however,

* Immediately after the introduction of the "reflex," mod-Scat ions, by-
changing the angle cf the facet, were made by the London opticians, so as
to adapt the instrument to their variously-angled objectives, similar modi-
fications were also made here in this country, by Messrs. Tolles & Spencer.
Three years ago the writer consulted a skilled artist with the view of mak-
ing the "reflex" in three separate mountings, changing the angle of the
facet in each. Nevertheless, the idea is Wenham's. The mere matter of
changing the angle of the facet would naturally occur to any one using the
instrument— J. E. S. January, 1878.

388 HOW TO SEE WITH THE MICROSCOPE.

notice the nature of one or two difficulties which may be said to
infest the observatory.

We are all familiar with the purpose for which the transit
instrument is employed, namely, to observe the transit of celes-
tial bodies across the meridian in which the transit is adjusted.
To accomplish this, it is evident that the instrument must be
permanently placed in that meridian ; bnt, unfortunately, the
block of stoue has yet to be found solid enough for the purpose.
Hence it is usual to ascertain the direction and amount of error
and thus correct the results obtained by observing with the
instrument while out of the plane of the meridian. The alti-
tude and azimuth instrument, too, requires frequent and careful
attention. To be assured that its object-glass may swing in a
vertical plane, observations are nightly made by observing a
distant star directly, and immediately afterwards its image as
seen in the mercurial horizon. By this means a truly vertical
line millions of miles in length is obtained.

Reflecting instruments constructed on the model of the sex-
tant, are cross-questioned by observations on east and west
stars, and errors due to eccentricity thereby avoided.

Not only do these painstaking men study their instruments,
but they in like manner study themselves, and their capacity to
observe is cross-questioned in the severest manner. It is to
them well known that the observations of some first-class
observers are constantly affected with a plus sign ; while, again,
those of other equally good observers are affected in a contrary
direction. This individual condition is called " personal equa-
ion," and has to be thoroughly known and compensated for;
and this you. must bear in mind, that the amount of error due to
personal equation is always comparatively small, and as a con-
sequence is only recognized in the observations of professional
experts, trained to machine-like, impassive regularity.

My initial remarks, in which the vt Nasmyth's " membrane of
the books wasVliscussed in a somewhat discursory manner, were
intended as an example, and to give you an illustration in refer-
ence to a radical evil, which has in times past tainted the obser-
vations of many who use the microscope— I refer to diffraction
lines and diffraction borders. To avoid these spectral, illusory

SUPPLEMENT. 389

appearances, is a consideration of the very first importance-
requiring, too, the employment of the finest object-glasses, and
that technical skill in the adjustment thereof, which is only
acquired by long practice ; and to this end the study of the dia-
t^maceae will be found in the highest degree advantageous.
Moreover, one must devote a good deal of study to this ghostly
parasite, which too often infests, and to a greater or less extent
defeats the unsuspecting observer. And here again the little
diatom will render yeoman's service.

Some months ago, Dr. Woodward, to whom we are all so
much indebted published in the London Monthly Microscopical
Journal, for the express purpose of displaying these illusory ap-
pearances, a lithograph from his photograph of Frustulia «Sax-
onica. The objective used by Dr. Woodward was an American
l-18th, and was the same glass with which his inimitable photo-
graphs of the 19th Nobert band were accomplished.

I took it for granted that the lithograph of Frustulia Saxonica
was made with the glass intentionally placed out of adjustment,
and for the purpose of creating these particular lines. A copy
of the London journal is placed at our service this evening, and
I invite your inspection of the plate referred to. The whole
shell of the diatom will be seen badly distorted, the strise badly
defined, and the diffraction lines are immense 1" *

*I may here remark that only a few hours ago my attention was called to
a report of a meeting of the London Microscopical Society, held April 5,
1876, and eported in the May number of the London Microscopical Journal.

Alluding to the photographs of Frustulia Saxonica, Mr. John Mayalt said:
" Kvery one who is familiar with the Frustul a Saxonica, photographs of
which Dr. Woodward sent in illustration of his paper in December, knows
it to be one of the most difficult test-objects —a diatom that ranks next to
Amphipleura pellucida. That particular form of Frustulia is one that I
have rare y seen resolved, except by lenses of the highest excellence. I
consider Dr. Woodward's photographs of it as in every way most remark-
able, evincing first-rate skill brought to bear on one of the finest known
lenses." It is hard to tell which is the most "reinarkaole," the photographs,
or this statement of Mr. Mayall's.

As there seems to be much difference of opinion as to these representa-
tions of Frustulia Saxonica, both at h 'me and abroad, a word or two maybe
admissable. When the lithographs first made their appearance in the Lon-
- don Monthly Microscopical Journal, one of our most talented experts wrote

390 HOW TO SEE WITH THE MICROSCOPE.

Now, after seeing and learning what can be accomplished
with a superior objective, when out of adjustment, it will be
instructive, and I shall beg your permission, by the employ-
ment of a superb glass, accurately adjusted, to show you a sim-
ilar, but more difficult tiaxoaica, as illuminated by the most
oblique beams my extremely thin stage will admit. Thus han-
dled the resolution of Frustulia Saxonica becomes one of the
most charming and fascinating objects that can well be imag-
ined. We shall thus see the frustule without sensible distortion
the striae displayed with such exquisite beauty of definition as
must command your admiration, and minus, too, the suspicion
of a diffraction line I

The attention of Andrew Ross, while examining Podura
scales with glasses of his own manufacture, was called to the
thickened edge, the " Nasmyth membrane " so plainly seen with
the non-adjustable glass he then employed, and to him are we
indebted for the collar adjustment now so common to all first-
class objectives.

Now, my friends, good object-glasses, like astronomers, have
their " personal equation." They alone are the ones to be most
affected by collar .adjustment ; an ordinary glass, furnished
with compensating screw, is scarcely superior to an ordinary
non-adjustable lens ; one may turn the collar through its entire
range, without sensible or corresponding change in definition.

me saying that he was surprised that Dr. Woooward should have allowed
the publication of prints giving such indifferent ideas of the work of
American lenses. I replied, that as I then understood the mat er, it was
Col. Woodward's intention to show the work of the objective purposely
placed out of adjustment, and I so continued to think at the date of the
above lecture, a fact obvious to the reader. I also suggested that the litho-
graphs might not fairly represent the photographs ; that if it was the case,
Col. Woodward would surely make the fact known. His silence, however,
authorized the inference that the original photos had not suffered at the
hands of the lithographer. I th nk I can now safely affirm that the general
opinion is that one of these lithographs was intended by Col. Woodward to
give a correct idea as to the appearance of P. S.ixonica when properly
resolved, i. e., that it might be contrasted with the others then presented.
Be all this as it may, I am prepared to asse:t that no one of said lithographs
gives any idea of the proper resolution of Fr.istulia Saxonica.— J. E. S.»
January, 1878.

SUPPLEMENT. 391

On the contrary, objectives of the widest apertures, and capable
of yielding intense definition, require the strictest attention to
their adjustment;. *

Nor is this all. It is quite possible to accurately adjust a first-
class objective, and, nevertheless, in this very act defeat the
maximum performance of a first-class glass I

When working with oblique light, the maximum performance
of a superior glass will be obtained at maximum aperture ; if
this maximum aperture obtains, with the systems '• closed," as
is often the case, it is then manifestly our business to use covers
of such thickness as will " correct" the objective at tk closed,"
and to work such a glass over thinner covers, requiring the lens
to " correct " at, or near *lopen point," would surely defeat its
best performance.

It being possible that we may have time in the course of the
evening to practically discuss this point, I have brought here an
objective which, in any position of its collar, has plus 180° of
aperture ; its balsam angles are at " closed," 97i°; at half way
between " open " and ;i closed " 95° ; at open point, 85°. It will
be an easy matter to demonstrate that this glass is defeated by
the thin covers of the Moller plates, over which the glass will
" correct " near to " open point," and conversely, of the decided
increase of definition obtained (and angle also) when worked
through a supplemental cover of sufficient thickness to cause
adjustment with the systems at, or near " closed."

I have brought here another, and a totally different objective;

this glass has a constant bals.im angle of 100° through nearly

the whole run of its adjusting screw. Manifestly, when using

this glass, there need be less attention paid to the thickness of

"cover, a fact which is demonstrated in practice.

* In an article contributed by Mr. P. EL Wenhara— ?ee London Micro.scop-
ical Journal for March, 1876—1 read, as follows : "The adjustment seems to
be a stumbling block for those advocating- an extra immersion theory. We
have now in use thousands of serviceabla tm.nerdion object-glasses, capa-
ble of denning most tests, and whi'.n have no adjustment, as they are set
for an average thickness of cover. They answer well, because in the im
mersion system the errors of cover aberrations aro nearly eliminated, and
with a balsam intermedium they would be inappreciable." (II!)

— J. E. S.

392 HOW TO SEE WITH THE MICROSCOPE.

These two objectives were constructed expressly for me, and
were especially intended for conjunct use— they are in truth,
companion glasses; either of them will display the 19th band
by oblique use of artificial light, and also the markings of An-
gulata by central lamp illumination. Of the two, the first-
named has the greatest working distance, and, for reasons
already given, will work at maximum performance over covers
l-50th of an inch in thickness, and in the hands of one thor-
oughly conversant with its functions, it is, perhaps, the most
generally useful glass.

I have here still another objective of plus 180° of aperture.
This glass was intended to be a compromise, and to serve to a
great degree the purposes both of the l-6th and the l-10th before
mentioned. The glass I now refer to has at " closed " a balsam
angle of 97! ; at open point, 92. The compromise is thus appar-
ent : this l-6th was made to my order for the gentleman who tills
the executive chair of this society. It asks no favors of M.
Nobert, nor of a centrally posed Angulata, and when one is con-
fined to a l-6th alone, a glass of this construction will prove of
great value.

These conditions, which have still greater force when we
include the work of various opticians, need attention and study
in default of which you m:iy expect diffraction lines and dif-
fraction borders; and, perchance, our old friend, the t; Xas-
myth," may put in an appearance !

I repeat, that it was the dominant purpose of these desultory
remarks to call yoiir attention to the importance of microscope
instrumentation, and to the manipulations connected therewith.
To the fact that it is a study, a profession in itself, and an
accomplishment that must be fully mastered at the outset,
before one can investigate with precision, or have claim to the
confidence of others. In point of fact, the most expert manip-
ulator will constantly have something to learn— there is no
landing place where one can stop and rest. The world pro-
gresses, and so should the microscopist— pari passu.

I take it for granted that nothing I have said will lead you to
suppose that I am opposed to the legitimate use of low-angled
objectives ; nothing could be further from my purpose. When

SUPPLEMENT. 393

properly used, for preliminary examinations, they are convenient
and useful, but for advanced work they should be abandoned,
and in favor of more inconvenient glasses of wider apertures.

A wide-angled lens, incapable of receiving and utilizing cen-
tral beams, is a faulty and undesirable objective ; it is, in fact,
but half a glass. And on the other hand, a low-angled objec-
tive, incapable of receiving lateral beams, is. in my opinion,
equally undesirable, unless, indeed, when we are prepared to
sacrifice force of definition to convenience of handling.

It must be admitted that there are functional and character-
istic differences in the performance of the two classes of objec-
tives; for instance, a wide-angled glass of relatively shorter
focal length will not see so far around an object as will one of
narrow aperture and longer focal distance. This, as well as
other considerations which might be mentioned, offer no rebut-
ting testimony to the statement already advanced, that the
principal advantage presented by the low angles is their con-
venience in manipulation.

In conclusion, I have to thank you for your kind attention to
the rambling remarks I have had the honor of presenting. Dur-
ing the few short hours that I have been in your city, the earth
has not had time to make one rotation ; but I have had a plenty
of time to experience and enjoy a generous hospitality. I am
now ready to show you the promised objects, and shall be happy
to see what ijou have to offer. You will find me ready, willing
and ardent to be taught, and in microscope matters be assured
I arc as absorbent as a sponge.

A CHAPTER ON ELEMENTARY PHYSICS.
(Dedicated to Prof. Hitchcock.)

Part First — The Sun. — "The luminous orb, the light of
which constitutes day ; the central body around which the earth
and planets revolve ; a celestial body which can be seen almost
any fair day through a piece of smoked glass."

I beg my friend to read the above little monograph on ele-
mentary astronomy carefully. Assuming his compliance with
this request, I go on to say that just after sundown this evening,
my attention was called to his really kind notice of myself, as

394 HOW TO SEE WITH THE MICROSCOPE.

well as my Dunkirk lecture. Allow me to assure you, my dear
professor, that although we have been pulling at opposite end*
of the rope for some months, the generosity I have experienced
at your hands has been vastly in advance of what I could have-
returned, and has placed me in position to receive any criticism
that you might offer with the best possible grace.

I now propose to jerk my end of the rope in a manner that
will make things lively with you I The fact is, when I get
after you with a ** sharp stick " you become unusually brilliant
with the jerk responsive I I like it.

I admit that you are one " who demands accuracy of expres-
sion in every branch of science" — "that the scientist has no
right to say what he does not mean, and he has no right to pre-
sume that his readers will understand him if he uses incorrect
language." I therefore have placed the above little monograph
on elementary astronomy at your service, and in timely season,
fearing otherwise you might be led astray by my use of the-
word u sundown "—you will see the point. It's true that Joshua
of old commanded the sun and moon to stand still, and the
story is found in a book generally admitted to be a classic, but
— no matter.

Now, professor, I fear that you do not practice what you
preach ; for I read (page 92), " if this question were put to a
thorough physicist * * * knowing nothing about
balsam or fluid mounts, etc." Isn't there an " impossibility "'
here V A thorough physicist knowing nothing, etc. There's a
screw loose somewhere.

liight on your next line is another jumble. Here is a want of
accuracy or what not — which is it ? You say " Must the scien-
tist .be led by the nose," etc. If this expression is accurate, 1
want you to tell me just how this kind of a thing is accom-
plished ; give me the p-r-a-c-t-i-c-a-l details, just as it would be
done in the flesh, including the " adopt " and the " teach "
— before an audience, too, without " apology" — and the why of
it. " It's the right and duty of every man of science to ask this
little question whenever it occurs to him." " The scientist has no
nqlit to say what he does not mean." Let us have the facts.

Part Second.— 180°, plus 180°, 180° + 45.° It is true, my dear

SUPPLEMENT.

395

sir, that in my Dunkirk lecture I did use the words " plus 180°
of aperture/' Now that select and intelligent audience (com-
prising physicists who did know something about " balsam
angles,") so far from demanding an " apology," generously and
unanimously gave me a vote of thanks. Curious, wasn't it ? I
remember well my delight in there meeting the veteran Dr. J.
W. Armstrong, Principal of the Eredonia Normal School, and
one of the leading educators of your state; another physicist,
too, who can talk intelligently as to " balsam angles," and who-
has made the apertures of objectives an especial study, and
who afterwards became one of my most valued correspondents.
Nor did we have any quarrel about the "plus 180Q." Most of
the audience had read about Joshua, and doubtless would not
baulk at such expressions as " sunrise '' or u sunset."

After all, professor, admitting that the " plus 180° " might
have courted son..e such gentlemanly criticism as it finally got
from you, I reckon I was as near right as Joshua. But before I
can lift you over this stile, I must scoop you up ! get you
together in some shape, so you can be handled. First of all,
you seem to put the 180°, plus 180°, 180° X 45°, all in one boat
together; you regard them as synonyms. And, secondly, I
have to learn some things from you.

Messrs. Tolles and Spencer you denounce because they mark
their objectives 180°, which you say is not only " impossible,""
but " absurd," and that one of these gentlemen (you don't say
which) attempts to lead the scientist " by the nose." And you
further say that one ot them (I don't know which, again,)
" might as well add 45° to said 180°.

Well, here is material enough to commence on. Now, my
dear professor, you maintain it to be the " right and duty " even
of every man of science to ask this little question whenever it
occurs to him the " why" part you know). That I have been
engaged in a controversy with you for months, demonstrates
my claim as a " man of science." You can't dodge that, and
the "occur " part is present and up to the high-pressure notch.

Now, I want to know " why " it is that 180° of aperture is
impossible ; "why " that plus 180° of aperture is impossible and
absurd. We have your assertions, but minus the ghost of a dem-
onstration.

396 HOW TO SEE WITH THE MICROSCOPE.

Why do you accuse Messrs. Tolles and Spencer of perpetrat-
ing acts that are absurd and impossible ; and why do you ven-
ture to hint that one of these gentlemen attempts to " lead
scientists by the nose," (whatever that may mean). The names
of Spencer and Tolles are revered by American microscopists,
and their unrivaled efforts in the improvement of object-glasses
have won for them a world-wide reputation. The chances are
that they know more of microscope optics than you and I put
together; and these are the men who mark their objectives
*l 180°." Why should there be " a law to prevent it ?"

Now, professor, if this 180° is impossible and absurd, will you
kindly inform the readers of this journal what figures Tolles
and Spencer ought to engrave on their wide-angled objectives
in place of the awful " 180°." Will you be kind enough to
name the extreme angle immediately adjacent, but not contact-
ing the impossible and the absurd ?

Again I read, " plus 180° does riot mean 97° balsam." Did I
assert this ? Now, I ask what does 97° balsam mean ? Let's
have it, and the "why" thereof. Unless you can tell me exactly
what the 97° balsam angle is, I shall not take any stock in your
above assertion.

Once more, you say that " true apertures can be measured
and definitely stated." I wish that you would tell Mr. Wenham
how the thing is done ; he tried for a whole year to measure one
of Tolle's objectives, without getting any two results alike !
But I am after you, not Wenham. I desire to learn from you
precisely what " true aperture is." When thus taught, then 1
desire to know by what physical process the same can be meas-
ured— " definitely" you know. "Accuracy" is the thing we
scientists want.

Now, my dear sir, I call on you to answer all of these inter-
rogatories, and when you shall have proven that ]80°, plus 180°,
or 180° X 45a, are one and the same thing ; when you shall
show that Messrs. Tolles and Spencer are asserting absurd and
impossible things, and more, are trying to lead scientists " by
the nose ;" when you shall prove that a thorough physicist
can know nothing of balsam or fluid mounts ; when you shall
have demonstrated that I should have apologized to my Dun-

SUPPLEMENT. 397

kirk audience ; when you shall have proven what 97° of balsam
angle is ; ditto as to " true aperture," and how to "definitely
measure " the same— then and not until then will I take the
" plus 180° " under advisement. Meanwhile we will be good
friends, and with Gen. Grant say, " Let us have peace." Don't
omit reading the reprint of Wenham's article on angular aper^
ture, pages 74 and 75.

CHOICE OF OBJECTIVES.

Ed. Am. Jour. Microscopy.— It was with real pleasure that I read
the article entitled " Dr. Carpenter on Angular Aperture," by
W. G. Lapham, Esq., in your May issue.

First of all, it is very satisfactory, from the fact that Mr.
Lapham speakes from a practical standpoint. The gentleman i&
an entire stranger to me, but the fact that his conclusions are
drawn from his personal, and, I doubt not, protracted experi-
ence, is evident from the ability with which he handles his
subject.

Your readers are well aware that I have often complained
that I have been compelled to fight theory with practice and
that no effort on my part sufficed to induce my opponents to
abandon their theoretical ideas, and to examine practically as to
the truth of the positions advanced by myself. In Mr. Lap-
ham, however, I resognize a co-worker, and although the
results he arrives at are not in perfect coincidence with my own,
I find nothing to criticize, but am simply desirous of further
comparing notes with the gentleman, in the hope that some-
thing to the advantage of microscopy may be developed.

I propose to present a few thoughts for Mr. Lapham's con-
sideration, requesting the gentleman to give them whatever
study and attention he may elect, and to advise your readers
as to the conclusions he arrives at; and, as before intimated,
nothing that I have to say ought to be taken in the light of a
criticism of his really excellent paper.

First, I desire to ask if Mr. Lapham does not attach too much
importance to the so-called " penetration." Is there in esse, any
such thing as "penetrations?" Perhaps it will be well, first of
all, to settle this point.

398 HOW TO SEE WITH THE MICROSCOPE.

Now I hold as follows : We will take, for example, two glasses,
both possessing the same amplifications and the same apertures ;
now of these two glasses, the one having the greater working
distance will exhibit structures situated slightly out of the
precise focal plane, or what amounts to the same thing, will be
less susceptible to slight changes in the focal distance, or again,
to use the words of Dr. Carpenter, will have the greater pene-
tration. In extreme cases, the item of aperture may be dis-
regarded. For instance, as stated in my Dunkirk lecture, a
spectacle lens of sixty inches focal length will be endowed with
greater penetration than a ToUes duplex objective.

But in the Dunkirk address, I did not avail myself fully of
the demonstration afforded by the spectacle lens, but now
invite Mr. Lapham's attention, thus : If it so be that with the
spectacle lens I am enabled to see with perfect clearness of
vision objects across the road, it will surely occur that when I
.attempt to read fine print, that the lens will defeat me. I will,
to be sure, see the lines of the print, will recognize the contour
of the book, and larger objects in immediate proximity, etc.
Here is an example from everyday life, to-wit : The glasses
suitable for reading will not answer for observations at a dis-
tance. True it is that with such glasses, with which we read
with ease, we may also see the general forms of things across
the road, yet they suffice not to render clearly the details thereof.
Hence we have all of us observed that many persons wearing
convex glasses often use two pairs of spectacles, one for near
and one for distant vision.-

Now in this everyday case we are taught a lesson, that, from
some cause or other, has been a slow one to acquire. First
*' penetration," in its naked aspect, is simply a function depend-
ing upon working distance; and secondly that "penetration,"
wtless accompanied with a certain amount of definition* is practi-
cally worthless. I ask Mr. Lapham's close attention to this point,
one that has been terribly overlooked.

Now, if Mr. Lapham's one-sixth of 180° happens to just
** turn the corner," i. e. have balsam angle, say, about 85°, I
would feel sure that a little observation would lead him to the
same opinions I have arrived at, and I only fear that he has

SUPPLEMENT. 399

chosen one of the highest balsam angles, in which case he will
have to fall back on his four-tenths. Nevertheless, let him, if
he will, try the experiment, and report as to whatever is gained
in point of penetration by the use of his one-forth of 50° over
and above what can be obtained by the use of the one-sixth, or
the four-tenths. The point I have to make is this— the one-
fourth of 50° will have the greater penetration (so-called, like
the spectacle lens) but will lack definition, to the end that more is
lost in the latter element than is gained in the former.

I state as a matter of fuct, but with no desire to bias the
further observations of Mr. Lapham, that I have used just such
a one-fourth as he describes, but have ultimately discarded it,
and in favor of a one-sixth marked by the maker 180Q, which I
find will do all the work (penetration included) of the one-fourth
of 50° and a great deal more besides. But behind this one-sixth,
I hold a one-tenth of 100° balsam angle in reserve, for work
where " penetration" is ruled out.

As to the other point suggested. Is there not undue weight
attached to this "penetration?" "With me, I have often been
obliged to take special measures to get rid of this function, and
for this purpose use the Beck illuminator, which gives me only
surface structures. I mention the fact, but am willing to admit
that a certain amount of - penetration" is at times desirable,
and should be provided for as perfectly as possible.

Mr. Lapham recommends a four-tenths of 100°. I have often
thought that such a glass, or a half-inch of the same angle,
would be desirable, and, as a luxury, arn still of the opinion. It
must be remembered that he very properly rules out the item
of cost ; wnile on the other hand I have made it a study to avoid
expense, where my opinion has been solicited in the matter of
selection of objectives.

Mr. Lapham recommends a certain number of low-angled
glasses, all others to be of the highest angles, and of the best
quality and well corrected. Why not amend this by insisting
that all glasses have the highest attainable angles? selecting
of such the one suitable for the work in hand.

Again, Mr. Lapham states that we have no need to consider
•objectives of lower power than the half-inch for " they are not

400 HOW TO SEE WITH THE MICROSCOPE.

made with angles sufficiently high to injure penetration." Here
is involved an error in fact, one quite pardonable too. Not Jong
since a German gentleman remarked to the writer that it seemed
to him that when the London opticians demonstrated a certain
opticial law, some Yankee optician would be just mean enough
to make an objective that would upset the whole arrangementl
And it is perforce of this /ac£ that Mr. Lapham becomes involved
in his very pardonable error. Now I have in my possession a
two- thirds of the Messrs. Spencers of 48° aperture. They have
lately made to my order an inch of 47°. The clear diameter of
both glasses is about the same; the working distance of the
two-thirds is 25-100ths of an inch, while that of the inch is but
13-100ths of an inch, arid the " penetration" of the latter (so-
called) is less than that of the 2-3ds. In fact the penetration of
the inch is "injured," as compared with one of 30°. The reader
will notice that Mr. Wenham's pet theory gets also into grief.
I assure Mr. Lapham that this new inch is a glorious glass, pene-
tration or no penetration.

Finally, I desire to extend to Mr. Lapham personally my
thanks for his instructive and interesting article. It will be a
pleasure, and, I doubt not, profit to compare notes with himr
and, in the words of my very generous opponent, Prof Hitch-
cock, I will add that all I desire is ''the facts." Mr. Lapham T
by the way, will be pretty sure to catch it, about that 180°, from
Prof. II., on the u impossible" and the tw absurd."

It may be well enough to add that my first impulse was to
write Mr. Lapham privately for an interchange of personal
experiences, but on reflection chose this, the more public plan,
hoping to enlist the attention of others in the same direction.

OLEOMARGARINE AGAIN.

Ed. Am. Jour. Microscopy:— The article giving " The Micro-
scopical Examinations of Oleomargarine," by Prof. Michels,
which appeared in a recent issue of this journal, was perused
by me with much interest, and I at once resolved to repeat the
experiments as detailed.

The first thing requisite was to secure authentic specimens of

SUPPLEMENT. 401

oleomargarine. In order to do this, I solicited the friendly aid
of a prominent gentleman of this city, who is also well known
in business circles in Xew York. I also wrote, independently T
to a gentleman in your city, urging him to obtain for me the
samples required.

Desiring also to procure a spacimen of genuine dairy butter,
I applied to a well-known citizen of this city, who procures his
supplies directly from a farmer.

After an interval of ten days, I was, in response to my solici-
tations, in. possession of three samples of oleomargarine, and
one sample of pure dairy butter. The three samples of oleo-
margarine are directly from the manufacturers at New York
city, and will be referred to as Xos. J, 2, and 3.

The four samples were subjected to examination under the
microscope ; tha objectives used were a l-4th inch of 100° by
Tolles, and Spencers late duplex l-4th of 180°.

Samples Nos. 1, 2 and 3, and also the specimen of pure dairy
butter, showed many crystals of chloride of sodium ; the crys-
tals furnished by the pure butter were, however, cleaner, and
more acceptable generally than those exhibited by Nos. 1, 2
and 3.

Samples Nos. 1, 2 and 3, in addition to crystals of chloride of
sodium, displayed other crystals, those of nitrate of soda being
prominent; while forms closely resembling crystals of choleste-
nne were found in considerable numbers.

Regarding Kos. 1, 2 and 3, it may be remarked that Nos. 1
and 2 were, to outward appearance, tolerably fair imitations of
genuine butter, and might by the ordinary purchaser be accept-
ed and bought as such. N"o. 3 was a poorer counterfeit, and
would probably be rejected by most buyers; but if mixed in
equal parts with the genuine article, the mixture would be likely
to deceive the purchaser.

In samples Nos. 1 and 2 the microscope displayed the
•' feathery crystals" (margarine) described by Prof. Michels,
although these were not constantly present in every field exam-
ined. By moving the slide, other fields were brought to view in
which these crystals were much more prominent than those
given in the cut accompanying Prof. Michels' paper. The crys-

;?(i Microscopy.

402 HOW TO SEE WITH THE MICROSCOPE.

tals of nitrate of soda and cholesterine (V) were to be seen in
every slide prepared from the samples named.

Besides the crystals named, samples Nos. 1 and 2 gave " sus-
picious cells " in large numbers, accompanied by shreds and
tissue fibres, many in a broken down condition, while others
seemed to be in a tolerably normal state, sufficient almost to
establish the presence of voluntary muscle. Bundles of these
fibres were closely examined with the duplex l-4th, under powres
as high as 1,600 diameters, with the endeavor to bring out
the transverse markings ; this was not accomplished— owing,
doubtless, to the nature of the vehicle (my observations in this
direction will be continued). Many of the bundles seen were
completely broken down, and the elementary fibres detached.

Sample No. 3, when examined under the microscope, displayed
fewei f the "feathery crystals;" nevertheless, this was the
most " suspicious " specimen of the three ; there were multi-
tudes of " suspicious cells," shreds and patches of tissue, in a
more or less broken down state. In one field I felt tolerably
sure of finding encysted hydatids. This slide unfortunately,
was accidentally destroyed by the water getting under the
cover.

To give an intelligent description of this material (No. 3)
would require far more time to its study than I have at my com-
mand at present ; but I hope to attack it again, and at an earl^
day. Suffice it now to say that this specimen contains verymani
" suspicious " elements, and that its behavior under the objec-
tive (here I also include Nos. 1 and 2), is— with the exception of
the crystals of chloride of sodium, and the presence of a few
fatty globules— totally different from that of pure dairy butter.

The sample of pure dairy butter gave fields just as represented
by Prof. Michels, with the exception that crystals of the chlor-
ide were almost constantly present.

Having established, to my own satisfaction, at least, the in-
tegrity ot the observations of Prof. Michels, I therefore hold
that the gentleman should be regarded in the light of a public
benefactor ; the matter he has presented will be found worth
serious and careful investigation.
In one of my recent lectures before the medical class of this

SUPPLEMENT. 403

College, on the Entozoa, I quoted (substantially) from Dr. Rob-
erts, as follows :

" A marvelous light has been thrown in recent years on the
zoological position of the Entozoa, chiefly by the researches of
Siebold and Van Beneden. It has been ascertained that the hy-
datid worm found in man, constitutes the encysted phase in the
developement of a very minute tape- worm which infests the
dog. The tape-worm in question is the Tcenia echinococcus ; the
entire adult animal is so small that it scarcely exceeds the size
of a millet seed. It consists of but three segments, of which
three, the last only is fruitful. When this segment arrives at
maturity, it is cast off, and a new one developed in its place.
Myriads of these worms are sometimes found in the intestine of
the dog, and their eggs are discharged in countless numbers
with the excrements, the eggs so discharged are scattered far
and wide ; and some of them find their way with the food into
the stomachs of men and other creatures suitable for their de-
velopment. Arrived there, the embryo is liberated ; and after
penetrating the mucus membrane, it burrows its way, or is car-
ried by the blood current to some distant organ, where it is
arrested. Having thus lodged itself, it presently reappears as a
hydatid vesicle, in which are developed the echinococci, as be-
fore explained. Dogs in their turn become infested with the
corresponding tsenia by feeding on the offal of slaughtered
sheep, pigs, etc., which had been infested with hydatids. The
echinococci therein contained develop in their intestines into
thetsenia echinococci, and thus the circle of transformation and
development recommences."

By similar cycles of transformation and development, do we
arrive at a class of parasites known in medicine as the ectozoa.
This term may be said to include, or be applied to, worms or
larvae of insects that have been introduced into the intestinal
canal by accident. Animalcules, such as the hair worm, grub
of the fly, may be mentioned ; also the larva of the bee, the spi-
der, etc. Among animals, the disease known popularly as the
botts, to which the horse is frequently a victim, is caused by
such animals swallowing the ova of the oestrus or gad-fly.

That oleomargarine manufactured from refuse animal fata,

404 HOW TO SEE WITH THE MICROSCOPE.

in the manner described by Prof. Michels, and at a temperature
not above 120° F., may be a highway through which fct eggs so
discharged " find their way into the stomachs of men, is too pal-
pably evident to need further comment.

INDEX.

Acetate of soda, solution, 329.

.Verne microscope, 84.

Adjustable objectives, 148.

Adjustable glasses, 129.

American stands, 17.

American stands compared
with German, 18.

American histological stand, 39.

Analysis, chemicals for, 322.

Analysis, chloride of sodium,
328.

Analysis for albumen, 337.

Analysis for glasses, 103.

Analysis, earthy phosphates,
331

Analysis, phosphoric acid, 330.

Analysis, sugar, 332.

Analysis, sulphuric acid, 331.

Analysis, urea, 323, 325.

Analysis for sugar, 335.

Angular aperture, what is it? 93.

Angular aperture denned, 93,
370.

Angular aperture illustrated,
94.

Angular aperture, how to meas-
ure, 95.

Angular aperture, versus work-
ing distance, 115, 121.

Angular aperture and central
illumination, 361.

Angular aperture and penetra-
tion, 118.

Angle high glasses, 103.

Apparatus for micro-chemical
use, 320.

Apertures, angular, 93,

405

Aperture, angular balsam, 123.
Artificial light, 187.

Balsam apertures, 12S.

Balsam angles, advantages of,
141.

Balsam angle, management of
257,

Balsam angle, and working dis-
tance, 142.

Balsam angle, low objective 144.

Baryta solution, 324.

Bausch & Lomb's microscopes,
50.

Bausch & Lomb's microscope,
professional, 53.

Bausch & Lomb's microscope,
students, 66.

Bausch & Lomb's microscope,
stands, 344.

Bausch & Lomb's objectives,
346.

Beck's microscopes, 72.

Beck's microscope stands, 347.

Beck's vertical illuminator, 217.

Beck's vertical illuminator, how
to use, 221

Binocular, objections to, 30.

Binocular, versus monocular,
29.

Biological microscope, 68.

Bull's eye condenser, 225.

Bull's eye condenser, how to use,
227.

Bullock's microscope, first-
class, "A. 1." 59.

40(3

INDEX.

Bullock's microscope, 59.
Bullock's microscope, D stand,

57.
Bullock's microscope, small,

best, 67.
Bullock's microscope stands,

343.

Carbonate of soda, 324.

Carpenter on object glasses, 97.

Centennial stand, Zentmayers,
34.

Centennial stand and A. 1. com-
pared, 63.

Central light and high angles,
257

Choice of objectives, 397.

Choice of objectives for regular
work, 202,

Chemicals for analysis, 322.

Chloride of sodium, 327.

Chromate of Potash, 327.

Collar adjustment, objections
to, 208.

Concentric rotating stage, 25.

Condenser, Bull's eye, 225.

Condenser, small diameter, 308

Contributions to the Medical
^N"ews, 358.

Covering glass guage, 216,

Covering glass, selection of; 213.

Daylight, how to use it, 1*3.
Diatoms, examinations of, 255.
Diatoms tor test, 251.
Diatoms, order for test, 254.
Diatoms resolution as objective

test, 249.
Diatoms resolution, with high

powers, 245.
Diatoms resolution, with low

powers, 245.

Diatoms, resolution, 243.
Draw tube, advantages of, 136.
Dry mounts, list of, 305.
Dry mounts, with high objec-
tives, 298.
Duplex glass, the first, 9.

Essentials of a reliable stand,
21.

Examination of morbid pro-
ducts, 206.

Examination of urinary depos-
its, 203.

Examination of oleomargarine,
400.

Eye pieces, 256.

Eye pieces high, 146.

Eye pieces fittings, 33.

Eye pieces solid, 156.

Eye pieces should fit loosely 204.

Eye training, 287.

Eye training illustrated, 239.

Family microscope, 57.
Fasoldt's micrometer, 357.
Fehling's solution, 333.
Ferro cyanide of potassium so-
lution, 329.

Field, flatness of, 126.
Fighting objectives, 117. 140.
Flatness of field, 126.
Four system glasses, 9.

G

Glasses, high angle, 103.
Glasses, high angle history of

100,

Glasses, testing aperture, 192.
German stands compared with

American, 18.

INDEX.

407

German student lamp, 187.

Handling objectives. 2-59.

High angles, 103.

High angles balsam, 125.

High angles, discursionof, 359.

High angles, objectives, 100.

High, eye piecing. 146.

High objectives, with dry
mounts, 298.

Higher powers, work with, 235.

History of high angle objec-
tives, 100.

Histological stand, 39.

Illumination, artificial, 187.
Illumination, daylight, 183.
Illumination small best, 189.
Illumination, sunlight, 186.
Illumination, varieties of, 183.
Illuminator, Beck's vertical, 217
Illuminator, modified, 219.
Illuminator, Wenham's reflex,

157.
Illuminator, Wenham's with

sunlight, 191.

Illuminator, Woodward's, 163.
Immersion, 125.

Kerosene oil immersion lens,
316.

Lens, Tolles' traverse, 179.
Lessons on seeing with the mi-
croscope, 261.
Lesson first, 261.

Lesson second, 262.

Lesson third, 265.

Lesson fourth, 266.

Lesson fifth, 268.

Lesson sixth, 270.

Lesson seventh, 271.

Lesson eighth, 273.

Lesson ninth, 274.

Lesson tenth, 280.

Lesson eleventh, 282.

Lesson twelfth, 284.

Low balsam angles, 144.

Low powers, working with, 225.

Management of high angles,

257.
Manipulations, microscopic,

157.

Marais' approximate tubes, 330.
Measuring bottle, 324.
Medium power of glass 144.
Micrometer, necessity for, 252.
Micrometer,, Fasoldt, 357.
Micrometer,*Rogers', 356.
Micro-chemical apparatus, 320.
Micro-chemical examination of

urine, 318.

Microscope, Acme, 84.
Microscope, Bausch & Lomb,

51.

Microscope, Beck's, 72.
Microscope, Bullock's, 59.
Microscope, dissecting, Beck's

79.

Microscope, "D," 67.
Microscope, economic, 72.
Microscope, family, 57.
Microscope, first-class A 1, 59.
Microscope, international, 348.
Microscope, investigator, 345.
Microscope, new biological, 68.
Microscope, new histological,

79.

Microscope, monocular vs. bin-
ocular, 80.

408

INDEX.

Microscope, national, 29.

Microscope, popular, 72.

Microscope, professional, 53.

Microscope students, 56.

Microscope, Sidle's, 84, 351.

Microscope selection, 147.

Microscope, Tolles , 47.

Microscope, Zentmayer, 34.

Microscope, use and abuse of
375.

Microscopic manipulations, 157

Mirrors, concave, 32.

Mirrors, hangings strong, 38.

Mirrors mountings, 32.

Mirrors, plain, 31.

Mirrors used as condensers, 229.

Mirrors where attached. 226.

Monocular vs. binocular, 29,
80.

Moller's test-plates, measure-
ments of, 253.

Mounting of objectives, 129.

N

Names of microscopic dealers,

341.
Robert's test-plate, 254.

Objections to mechanical stages

24.

Objections to binoculars, 30.
Objectives, adjustable, 148.
Objectives, broad guage, 230.
Objectives, balsam, 141.
Objectives, choicetof, 397.
Objectives, Dr. Carpenter on

97.

Objectives, fighting, 117, 140.
Objectives, high angle, 97.
Objectives, high angle, testing

of, 107.
Objectives, low balsam angle,

144.

Objectives, one-sixth preferred

to one-fiftieth, 109.
Objectives, immersion, 125.
Objectives, experience with,

202.

Objectives, for physicians, 207.
Objectives for regular work,

202.
Objectives, test with diatoms,

249.
Objectives, testing aperture of

192.

Objectives, testing, 198.
Objectives, wide angle, what is

it V 137.
Objectives, working distance

of, 108.

Objectives, mounting, 129.
Objectives, oil immersion, 310,
Objectives, Spencer's, 353.
Objectives, Tolles', 354.
Objectives, performance of, 368.
Observer's position, 246, 289.
Oil immersion objectives, 309.
Oil immersion, objectives, expe-
rience with, 315.
Oil immersion objectives of

Zeiss, 310.
Oleomargarine examinations,

400.

Penetration and angular aper-
ture, 118.

Physicians, objectives best for,
207.

Physics, elementary hints on,
393.

Pod ura, scale resolution of, 299.

Position of observer, 246,289.

Professional microscope, 53.

B

Rising of the object, 276.

INDEX.

401)

Reaction of urine with tests,

339.
Rogers' micrometers, 356.

Selection of covering glass, 213.

Selecting a stand,

Sliding tube, advantages of, 44.

Short tube stands, 25.

Snuill light best, 189.

Small kerosene lamp, 189.

Society screw, 232.

Society screw not sufficient for
high angles, 88.

Specific gravity and tempera-
ture, 340.

Spencer's objectives, 353.

Spencer's one inch of 50°, 230.

Stage, thin, improvised, 39.

Stage swing and mirror best,
91.

Stage, concentric, rotating, 25.

Stage, mechanical objections to
24.

Stage, room necessary, 26.

Stage used by the author, 27.

Stand, Acme, 84.

Stand, American, 17.

Stand, American Centennial,
34.

Stand, Bansch & Lonib's, 50.

Stand, Beck's, 72.

Stand, Bullock's, 59.

Stand, essential of a reliable
21.

Stand, Economic, 72.

Stand, Histological, 79.

Stand, "D,"67.

Stand, Investigator, 345.

Stand, International, 348.

Stand, large and small, 26.

stand, large " BB," 47,

Stand, large " A," 48.

Stand, new biological, 68.

Siand, new National, 80.

Stand, first class " A. 1." 59.

Stand, small best, 67.
Stand, popular, 72.
Stand, Sidle's, 84.
Stand, Tolles', 47.
Stand, students', 49, 56.
Stand, small and cheap, best,

92.

Stands, with short tubes, 25.
Stands, Zentmayer's, 34.
Students microscopes, 49, 56.
Sunlight illumination, 186.

T.

Table for work, 229.

Temperature and Urine specific
gravity, 340.

Testing high angles, objective,
107.

Thin stage necessary, 90.

Tight fitting eye pieces, 204.

Tolles' first duplex, 9.

Tolle's microscopes and objec-
tives, 354.

Tolles' traverse lens, 179.

Tolles' large "• BB "stand, 47,

Tolles' large kt A " itand, 48.

Tolles' students' stands, 49.

Traverse lens, 179.

Tube casts,, no genuine seen,
319.

Tube sliding, advantages of,

U.

[Jrinnry constituents, propor-
tion of, 339.

Urinary deposits, examinations
of, 203.

Use and abuse of the microscope
375.

V.

Volumetric analysis, 318.

410

INDEX.

w.

Weights recognised, 321.

Wen ham 'a reflex illuminator
157.

Wide apertures, lessons in the
use of. 261

Wide apertures, management
of 258.

Wide angle objectives, 137.

Wide angle objectives and col-
lar adjustment. 139.

Wide angle objectives and illu-
mination. 140.

Wide angle objectives and
working distance, 137.

Work table, 229.

Working with higher powers,
235.

Working with lower powers,

Working distance of high an-
gles, 137.

Working distance of high bal-
sam angles, 143.

Working distance of objectives,
108.

Working distance vs. angle
aperture, 115,121.

Woodward's illuminator, 163.

Woodward's illuminator modi-
fied, experience with, 177.

Z.

Zentmayer's stands, 34, 355.

Zentraayer's American Centen-
nial, 34.

Zentrnayer's American Histo-
logical,39.

SPECTACELS ;

AND HOW TO CHOOSE THEM.

BY C. H. VILAS, A. M., M. D.

Professor of Diseases of the Eye and Ear in the Hahnemann Medical

College, and Ophthalmic and Aural Surgeon to

the Hahnemann Hospital,

Chicago, etc., etc.

This book is full of interest and instruction to readers of all
classes. Designed more especially for the profession, it never-
theless does not deal in technicalities or obscure terms and
will doubtless lind a large demand among non-professional
people.

In a clear and comprehensive manner it treats of a most
important subject, a subject concerning which, far too many er-
roneous and dangerous notions prevail. It's aim is to dissemin-
ate knowledge, and to prevent the common haphazard custom
of choosing Spectacles, a custom so often disastrous to vision or
fruitful to discomfort. The Author points out how, within a
comparatively recent period, what was once veiled in mystery,
has attained a sure place among the sciences ; how the know-
ledge of the proper construction, adaptation, and uses of Spec-
tacles has grown to great proportions, and has led to a revolu-
tion in the treatment of eye affections. Many popular delusions
will be dispelled by reading this book. It is valuable alike to
the physician and the layman. The former may utilize it in
practicing his profession ; the latter will prepare himself to
avoid errors fatal to vision.

All the new and useful cases of trial lenses are described and
illustrated and their respective merits and demerits are pointed
out. It is clearly shown how the low prices, at which a good
set of trial lenses can be obtained, will enable the physicians in
general practice to give attention to the fitting of Spectacles
and to treating ordinary defects of the vision, thus preventing
the frauds so often practiced by itinerant venders.

The Author's well known accomplishments in this depart-
ment of science, have eminently prepared him to skillfully
treat so important a subject. The work is illustrated and full
of practical hints.

Price bound in cloth, $1.00.

DUNCAN BROS., Publishers.

131 & 133 8. Clark tit., CHICAGO.

THE NURSE;

OK,

HINTS ON THE CARE OF THE SICK;

INCLUDING MOTHERS AND INFANTS, AND A DIGEST OF
DOMESTIC MEDICINE.

By CHARLES T. HARRIS, A.M., M.D.
Elegantly bound in Cloth - Price , 60 cents.

"Every Nurse should have a copy."

"Every Mother should possess this useful work."

4i It will not hurt physicians even to glance over the pages devoted to
mothers and nurses, and this little treatise ought to become one of the
tracts domiciled in every household." — North Am. Journal of Homoeopathy.

This is a valuable volume to professional nurses and mothers, the natural
nurses. The author strongly advocates the importance of intelligent, self-
sacrificing- nurses. The instruction the book contains is cle rly arid con-
scientiously given.— Boston Inventors & Manufacturers' Gazette.

Such a work is very much needed. It is simply and clearly writt en, giv-
ing hints on all the points which a nurse ought to know. We cordially
recommend this little work to the attention of mother-* and nurses who will
find it a valuable vade mecum.— Monthly Homoeopathic Review, London.

A neatly printed, handsomely bound work of over a hundred pages,
written with the endeavor, as stated in the preface, to make their scope
"broad»enough to cover the wants of two classes; the conscientious and
ambitious professional nurse, and .the faithful and loving mother." The
matter of the worK, from the introduction to the last page, seems well and
carefully written and very sensible. — Ypsilanti Sentinel.

It is written in simple and concise style and free from all technicalities,
and abounds in valuable facts and directions to those who have health as
well as to those who are called to nurse in the sick room. It is a book every
mother could read with profit. Skilled and trained nurses are not a ways in
reach, and the lives of those deartoihe family are of ten imperiled by simple
ignorance of what every intelligent person should know. Good nursing,
every intelligent physician will say, is of more value than drugs. The hand-
some lit tie volume should find its wav into many homes, and by the intelligent
observance of its rules, blessings alone will result.— The News.

K5^~May be ordered through your physician, or newsdealer, or will be sent
to you direct on receipt of price.

DUNCAN BROS., Publishers,

113 Madison and 131 & 133 Clark St., Chicago.

HOW TO BE PLUMP.

OR

TALKS ON PHYSIOLOGICAL FEEDING.

BY

T. C. DUNCAN, M.D.,

Author of a Professional Treatise on Diseases of Infants
and Children and their Homoeopathic Treat-
ment; Editor " United States Medical
Investigator, etc. etc."

Finely bound in Cloth .... Price, RO rents.

It is an admirable work on hygiene, as faras it relates to eating-Oftio.
Farmer.

These " Talks " have their own charm, for most of us like to be plump.
— Women's Journal, Boston.

Certainly all thin people should ponder well its suggestions and put them
into practice.— Voice of Masonry.

A brochure wh-ich many persons of lean inclinations will be glad to read
and may be able to profit by.— Banner of Light.

The little volume contains n uch sensible professional advice upon
healthy and morbid digestion, and the occasions of it.— Zion's Herald.

The book i? intended to indicate how anyone may become fat, fair and
jolly, and a careful perusal affords proof th--»t the author is fully conversant
with his subject, and that he has done it full justice.— The C-nOago Grocer.

It is a common sense volume, that believes in rational and practic I
methods of preserving- health, beautv and happiness. It is not a receipt
bock of impos ibilities; it is a bright, genial book, that understands itseif
from first to last.— The Chicago Cosmopolitan.

We do most warmly applaud its purpose, and especially commend its
philos phy to theunnaturahy 1 an, and sti.l mor • to mothers in the training
of delica e children whose physical stamina hardly equals that of a full-
grown rye-stalk. Theirs is a leanness to be built up into steady strength
and picturesque plumpness of limb and face.— The Standard.

CHICAGO, Sept 18, 1878.

The case referred toon page 45 of " How to be Plump" is our little boy,
who was certainly rescued from death's door. This summer he began to rim
down again. After Dr. Dun an had tried several medicines without benefit
he gain advised "inunction," and again with the same happy effect. The
little fellow is now plump and well. CHAM,KS WALKS.

8^~May e ordered through your physician, or newsdealer, or will be sent
direct on receipt of price.

DUNCAN BROS., Publishers,

113 Madison and 131 & 133 Clark St., Chicago.

" DOCTOR, WHAT SHALL 1 LA 7. r

~A~

HAND BOOK

or

DIET IN DISEASE.

BY CHAS. GATCHELL, M. D.,

Formerly Professor of Practice, University of Michigan.

It is highly endorsed by the Profession and Medical Press.

How often do we hear that same question, Doctor; what shall I eat? and
though there are textbooks enough on the Pathology and Treatment of
Diseases, there is hardly ever a word found in them about the Hygiene in
Disease. Gatchell as a tracher, found out this want, and thus piobably
originated this little treatise, for which we most heartily thank the
author. We consider the recipes in it a, little Materia Medica for itself, but
follow instructions closely ; not quantity, but quality of food deserves our
consideration. — North American Journal of Homwpathy.

MILWAUKEE, Wis.

"I consider your work on "Diet in Disease" to be the most practical, and

therefore the most useful, work on the subject with which I am acquainted.

No physician should be without it; every mother should have it. It is in

u se in many of the households in which I practice." C. C. OI.MSTEAD, M. D.

President of the Wisconsin Homozpathic Medical Society.

"This work is plain, practical and valuable, It is really a clinical guide
on diet, and one the profession will find reliable and correct."— United
States Medical Investigator.

"By far the best work on the subject in our literature. I find it of use
every day. I want one in every household in which I practice."
Oak, Park, III. F. G. FOLSOM, M. D.

"Evidently much investigation, thought and carefulness have entered
ipto the production of this work, and we believe it to be worthy a place in
every household." — The Magnet. .

* * * "We have carefully examined the work and svall cheerfully
recommend it for family use. The directions as to what food and drinks,
and modes of preparation are very judicious." * * * Resp. Yours,

Janesville, Wis. DR. G. W. CHIITENDEN & SON .

Professor Charles Gatchell's Manu&l of 'DIET IN DISEASE' is the best book
on the subject for the people. It contains in 160 pages an astonishing
amount of condensed information on a subject of great importance, and
one but little understood. Its style ia admirable, pithy and to the point.
The book has no padding about it and deserves an immense sale."

SAMUEL POTTER. M. D.,
President, Milwarikee Aeademy of Medicine,
Aathor of Index of Comparative Therapeutics, etc. etc.
ty Sent free on receipt of price, $1.OO.

DUNCAN BROS.,

131 & 133 S. Clark St. CHICAGO.

THE
FEEDING AND MANAGEMENT

OF

INFANTS AND CHILDREN,

AND THE

HOME TREATMENT OF THEIR DISEASES.

By T. C. DUNCAN, H. D.,

PRESIDENT OF THE AMERICAN P.EDOLOG"ICAL SOCIETY. CONSULTING PHYS-
ICIAN TO THE CHICAGO FOUNDLINGS' HOME. CLINICAL LECTURER
ON DISEASES OF CHILDREN. AUTHOR OF UA PROFESSIONAL
TREATISE ON THE DISEASES OF CHILDREN" (2 large
volumes). EDITOR OF THE UNITED STATES
MEDICAL INVESTIGATOR, 'ETC., ETC.

MRS. J. E. JOICE writes : "I find it a very useful book and full of practical
information, especially about diet for children."

L. PAULY M. D. writes : "I am glad to know that we are going to have a
German edition of The Feeding and Management of Infants and Children.
I know of no such book in German of a similar character and am confident
that it will be welcomed by all thinking German mothers."

MRS. T. WILCE, President of the Mother's Society of Chicago, says : "It
is the most instructive book for mothers and < specially young mothers,
that has come to my notice and I earnestly advise all prospective mothers
to read it. Would to God that I had had such a book years ago.

MRS. H. E. REDEKER of Kenosha, Wis., writes: "I think it is the bestwork
of the kind I have seen. lam glad that 1 shall have Dr. Duncan at hand
ready to consult at any moment for I have the greatest confidence iu all
that he says. It is a book that it seems to me every mother would like to
have."

DR. EDWARD CRANCH, Secy, of the American Paedological Society (com-
posed of the leading physicians interested in Children's Diseases), says :
*' I have carefully examined the work and unhesita ingly pronounce it a
most necessary book for all families. It ought to go into every intelligent
household where the health of the little ones is valued."

'•Prevention is better than cure," and many a babe will fare better if the
mother follows the advice given by 'hat great friend of our babies, T. C.
Duncan. It is a work, whose first part we can fully endorse, and since I
studied th< se alkaline and acid babies, my endeavors are to have my little
patients alkaline. The artificial feeding of children is a most interesting
study even to an old physician and only by following closely the rules laid
down, can we prevent the necessity of studying the secoud part. — North
American Journal of Homcepathy.

The Organon of London, Eng., says: "Paedology is Dr. Duncan's Specia-
lite and we may be sure that what he writes on this subject contains some-
thing worth reading. His Encyclopedia on Diseases of Infants and Child-
ren is a work for the profession ; this one is for the public, and a better
work on the subject we do not remember to have seen. * * Every day
rules for diet and regimen generally, are what the public should know, and
without these the skill of the physician is daily thwarted ; iu this respect
Dr. Duncan has performed his work admiiably. The book is elegantly
gotten up."

SOLD ONLY BY SUBSCRIPTION.

Price, Cloth, $2,00 ; Half Morocco, $2,75.

Agents wanted in every town. Ladies sell it rapidly. Address for terms
and territory,

DUNCAN BROTHERS,

131 <& 133 Clark 8t., CHICAGO.