1887.] MICROSCOPICAL JOURNAL. 9 
The eye-piece 1 is only made for the Continental microscope and 27 only 
for the English, as the former would be too large for the English body-tubes, 
while the latter would have an inconveniently short focus with the Continental. 
The eye-pieces of unusually low power designated ‘ Finders’ serve for the 
purpose of reducing to its lowest limits the available magnification with each 
objective, thus facilitating the preliminary examination of specimens and 
avoiding the labor of searching for particular points with high powers. The 
Finder eye-piece enables an objective to be employed with its own proper 
magnifying power, z. e., as if it were used as a magnifier without an eye-piece. 
In both, the diameter of the field of view amounts to fully a fifth of the focal 
length of the objective used with a relatively small angle, 12° in 1 and 24° in 
2. This is particularly favorable for rapid searches. 
These Finder eye-pieces are of special service for water and oil immersion 
objectives, where great inconvenience is caused by having to change an objective 
already adjusted for another of longer focus. 
The working eye-pieces for regular observation are likewise of entirely new 
construction. They commence in both series with a magnifying power of 4, 
and are convenient to work with, even inthe highestnumbers. The eye-point 
in all lies so high above the upper surface of the eye-lens and the diameter 
of the lens is so large that the usual inconveniences attending the use of the 
eye-piece of short focus are completely obviated. 
The ordinary drawing prisms, and particularly the Abbe camera, may be 
used without difficulty on Nos. 4 to 18 inclusive. 
All the eye-pieces are supplied in cylindrical mounts, the external diameter 
of which is 23.3 mm. for the Continental body and 35.0 mm. for the English. 
Adapters to fit them to larger bodies can be made by any workman. 
On each eye-piece is engraved the magnifying power, the focal length, and 
the tube length for which it is adapted, as well as the name of the firm. 
Table of magnifying porvers of the apochromatic objectives, with the compensating 
eye-pleces for a visual distance of 250 mm. 
Focal length Finder eye-piece. Working eye-piece. | 
| of obj. UES. hehe A ele the teal 
es nee 4 8 12 18 27 | 
| Lae ee ee) eee Pe 
21 42 83 125 187 281 
301 62 125 187 281 — 
42 83 167 250 375 562 
62 125 250 375 562 _ 
83 167 333 500 75° 1125 
125 250 500 750 1125 — 
167 333 667 1000 | 1500 _— 
200 400 800 £200 “1800 — 
250 500 1000 1500 2250 = 
Projection eye-pieces.—For such purposes as require the projection of a 
real image, but more particularly for overcoming the inconveniences which 
arise in photo-micrography when the objective alone is employed, as also in 
the use of the ordinary eye-piece or amplifier, a specially constructed projec- 
tion series is supplied, which externally resemble eye-pieces, and fit into the 
body-tube of the microscope in the same manner. 
They consist of a convex lens and a compound system, which, like the 
apochromatic objective, is most carefully corrected both spherically and chro- 
matically, and is entirely free from any secondary chromatic aberration, and 
free from difference of focus between the visual and chemical rays. Between 
the convex lens and compound system a diaphragm is introduced for limiting 
the field. The system can be made to approach or recede from the diaphragm. 
When used to project an image on a screen for demonstration, or upon a 
photographic plate, the objective of the microscope remains exactly in the 
