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  CATALOGUE No. 40.

  MICROSCOPES
  AND
  ACCESSORY APPARATUS.

  ERNST LEITZ
  WETZLAR
  GERMANY.

  Founded in 1850.

  Branch Offices:
  NEW-YORK:                CHICAGO:            BERLIN NW.
  411 West 59th Str.    32-38 Clark Str.    45 Luisenstrasse.
  30 East 18th Street.

  1903.

  ="Highest award"= Worlds Columbian Exhibition =Chicago 1893=.




  Contents.


  New constructions                            5
  Objectives and Eye-pieces                    7
  Stands                                      16
  Illuminating Apparatus                      20
  Complete Microscope Outfits                 24
  Microscopes for Mineralogical Research      57
  Dissecting Microscopes and Lupes            62
  Apparatus for Blood Examinations            70
  Micrometers                                 73
  Drawing Apparatus                           74
  Mechanical Stages                           78
  Photo-micrographic Apparatus                82
  Projection Apparatus (Edinger)              84
  The Large Projection Apparatus              87
  Microtomes                                  92
  Miscellaneous Accessories                   99
  Publications                               104
  Index                                      105




  Notice.


All previous editions of this catalogue are superceded by the present
one, which should be exclusively used in ordering.

Orders will be filled at once after their receipt.

In ordering care should be taken to give the =number= of each article
desired and to state listprice.

To avoid delay and misunderstandings, we request that name and address
be plainly written.

Goods are forwarded at the expense and risk of the purchaser.

Our instruments for use in =Universities, Colleges, Schools= &c. of the
=United States= are by law free of duty and we shall be pleased to make
specially low quotations for such orders.

  ERNST LEITZ.




  New Constructions.


Since issueing our last catalogue, a number of new apparatus and
accessories have been added. The following are the more important ones:

1. A completely =new stand "A"= with extra fine micrometerscrew
transmitting its movement directly to the tube. The stand is of elegant
appearance and large dimensions, making it especially well adapted for
work in photo-micrography.

2. =Stand I= is now fitted out with the new special fine adjustment (each
division {1/1000} mm).

3. =Stand II= with round centering stage.

4. =Stand IV= is replaced by a model of larger size.

5. =Photo-micrographic apparatus= for use in horizontal and vertical
position, having joint for inclination, large size bellows and
plateholder.

6. =Large projection-apparatus= for electric lamp of 30 Ampere with triple
collecting lens of 210 mm aperture.

7. =Objective 1 a= with adjustable mounting and changeable magnification.
It is an excellent objective of low power for general purposes, having a
comparatively short working distance.

8. =Objective 1 b= with changeable magnification of lowest power, as far
down as two diameters. It serves for drawing extended sections and
specimens.

9. =Saccharimeter after Mitcherlich= improved form.

10. =Trichinoscope=, projection-apparatus of strong and simple
construction.




  =Preface.=


Our American Branch house in New-York under the management of Mr. Wm.
Krafft has now been established for over 10 years. This period has
witnessed a gradual development of our business in the United States,
making it necessary to establish some years ago a Western Branch in
Chicago of which Mr. R. Gibson has charge.

The cordial reception our firm received has been most gratifying and we
take this opportunity to thank our many patrons for their kind
consideration.

It is our aim to co-operate with the scientists and construct new
apparatus to meet their needs or improve others wherever this is
possible.

The foregoing list of additions and improvements made since issueing our
last catalogue is proof that we spare no time nor labor to hold pace
with the increased wants of modern times.

We have now manufactured and sold over 71000 compound microscopes and
31000 oil immersion objectives, a large number of which are used in the
laboratories of Universities, Colleges, and other Educational
Institutions of the United States.

We are prepared at New-York and Chicago to repair our instruments or
make alterations at short notice and at lowest prices. The optical part
of a microscope should invariably be sent to the maker, as he is best in
a position to repair same and has an added interest to bring a lens back
to its original quality or even improve it.

Microscopes, bacteriological apparatus and all other scientific
instruments or preparations expressly imported for use in educational
institutions are exempt from duty.

Catalogues may be had on application by addressing:

  =ERNST LEITZ,=

  NEW-YORK               CHICAGO
  411 West 59th Street   32 Clark, Cor. Lake Street.




  =Objectives and Eye-pieces.=


In the manufacture of our objectives only such glass is employed as has
been subjected to the most rigid scientific tests. By these the exact
index of refraction and the exact degree of dispersion of the glass are
determined, and with these data available it is possible to very
perfectly correct both spherical and chromatic aberrations while still
making use of wide angular apertures in the objectives.

The precise mathematical calculation, combined with accurate
systematical working and testing methods, make it possible for us to
guarantee our objectives to be all of equal and excellent quality.

Every objective before leaving our hands, is subjected to the most
careful test, and only such lenses as are of the highest grade, are sent
out.

For the past seventeen years we have used glasses manufactured by Schott
& Co. of Jena. This glass has many points to recommend it for the
construction of optical instruments, and only such kinds are employed by
us, which have for many years been thoroughly tested as to their
durability.

Our lenses are therefore absolutely permanent. Objectives of the earlier
type which have become cloudy, we shall gladly repair.

[Illustration]

The three illustrations given above afford an idea of the plan of
construction of our achromatic objectives.

The first figure represents the plan of our low power objectives, and it
will be noted that they consist of two doublets, or triplets each
carefully corrected.

The central figure shows the construction of our high power dry
objectives. A hemispherical front lens is combined with two doublets or
sometimes triplets. The front lens is the chief magnifier of the
combination, while the other lenses serve to correct the various
aberrations.

The Oil-immersion, represented by the last illustration consists of a
front lens, hemispherical, behind which is a meniscus, which is in turn
followed by a doublet and a triplet, these latter acting as the
correcting lenses of the combination.

We manufacture both =Achromatic= and =Apochromatic objectives=. They differ
in that the glasses made use of in the apochromatics and the manner in
which they are combined permit a more perfect correction of chromatic
aberration. This advantage is not gained without a certain sacrifice of
simplicity in construction; by avoiding the use of flint glass having a
high refractive index and substituting materials to take the place of
crownglass. The apochromatics as a matter of fact do resolve the fine
markings of test objects (butterfly scales and diatomes) somewhat more
clearly than the achromatics, but the difference is slight and in
ordinary stained microscope preparations is hardly detectable.

The correction of both achromatics and apochromatics is complete. The
ordinary Huyghenian eye-pieces are consequently well adapted for use
with the objectives of either construction. Only with the highest powers
is it desirable to make use of the so-called "compensation" eye-pieces.

The achromatics and Huyghenian eye-pieces are also well adapted to the
requirements of photomicrography, special objectives being unnecessary
for this purpose. This statement is substantiated by the excellent
results obtained with our achromatic objectives, as shown in the
photomicrographs accompanying our brochure on
Photomicrography:--"Anleitung zur Mikrophotographie".

In making use of the higher power objectives--from No. 5 on--it should
be remembered, that the lenses are corrected for cover glasses of 0,17
mm in thickness and for a microscope tube-length of 170 mm. When using
the oil-immersion objectives it is particularly desirable, that this
exact tube length should be employed. With a view to facilitate the
adjustment of the tube-length the draw tubes of all our larger stands
are graduated in millimeters, the scale indicating the exact length of
the microscope tube in any given position of the draw tube. In this
connection it should be remembered, that the width of the collar of the
nose-pieces is 15 millimeters, and that consequently, when a nose-piece
is attached to the tube the reading of the draw tube scale should be 155
mm instead of 170 when the adjustment is proper.

[Illustration: Figure comparative merits of the dry and immersion
systems.]

The above sketch may serve to make clear the advantages of the immersion
objectives over those of the dry series. It is intended to represent
diagrammatically a section through a cover-glass and the front lens of
an objective, one half of the figure representing the conditions present
in the case of the Oil-immersion, the other those which are present in
the dry objectives. It will be noticed that by the interposition of a
drop of oil of the same index of refraction as the glass between the
cover-glass and the objective the refraction which occurs in the dry
system when the light leaves the upper surface of the cover-glass is
done away with. Since this second refraction is attended with much loss
of light it must be evident, that in the immersion system a much greater
quantity of light enters the objective than is possible, other things
being equal, in objectives of the dry system.

If we let _u_ represent one half the angular aperture of an objective,
represented in the diagram by _D'BN_ in the case of the immersion, and
_n_ the index of refraction of the medium interposed between the
cover-glass and the objective we have in the formula _n_ sin. _u_ a
mathematical expression of the optic power of the various systems of
lenses, or in other words for what is designated the numerical aperture.

The following table gives the numerical apertures of objectives of the
various systems and of various angular apertures. In the dry system
_n._, representing the index of refraction of air is taken as 1.00; in
the immersion systems _n_ equals 1.33 for water, 1.52 for cedar oil and
1.66 for monobromnaphthalin. A glance at the table will suffice to show
the great advantage which the immersion objectives have over those of
