ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
623 
the usual size, viz. 11 in. in diameter. The mount holding the mirror 
is gimballed in a stout ring of well-hammered brass. Between the 
gimbal and the screw is a brass collet which fixes the gimbal on to the 
sliding tube. The tail-piece on which the mirror slides is shown in 
fig. 64. 
The tripod (fig. 65) should be 5/16 in. thick. One of the holes of 
the tripod has a saw-cut at right angles, and is fitted with a screw to 
produce the required tension on the axial motion of the instrument. 
The lower field lens of the eye-piece should be 2^ in. solar focus, 
and the eye or upper lens in. focus. Length of tube and diameter of 
stop are given in fig. 66. 
(3) Illuminating- and other Apparatus. 
Koristka Camera Lucida after Nachet.* — In the camera lucida 
represented in fig. 67 the prism has one surface gilded and transparent 
according to the design of Prof. G. Govi. The layer of gold allows of 
Fig. 67. 
the transmission of the image given by the eye-piece, and at the same 
time reflects to the eye the image of the pencil and drawing paper. 
(4) Photomicrography. 
Koristka Photomicrographic Cameras.! — The large model seen in 
fig. 68 has a double bellows, each half of which has an independent move- 
ment. The stage supporting the stand is of cast iron and is provided 
with levelling screws. The arrangement for moving the micrometer 
screw at a distance is of special construction, and can be used for mag- 
nifications of more than 5000 diameters with as much precision as if the 
head of the micrometer screw were moved directly by hand. The camera 
is provided with a ground-glass plate and a transparent plate for more 
exact focusing, and with slides of sizes 9 by 12, 12 by 16, and 18 by 
24 cm. The total length of the camera when fully extended is 1*80 m. 
The small model, shown in fig. 69, has a base-plate with guides 
* F. Koristka, Catalogo Illustrate Descrittivo, N. 7, Milan, 1894. f Op. cit. 
2 u 2 
