ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 



281 



Movement of the plane of the image, and also of the Microscope end 

 of the camera is effected by pinions acting on a strong rack. Both 

 halves of the camera are arranged for plate-holders of 24 by 24 cm. 

 which, however, by the addition of frames can be used for plates of any 



smaller size. Two adjusting plates, one of ground glass, and the other 

 transparent, and provided with a cross on the Microscope side, serve for 

 the coarse- and fine-adjustment of the image. A third plate-holder can 

 be added, which for the purpose of ascertaining the best time of exposure, 

 permits a great number of proofs to be taken one after another on the 

 same plate. To this end the holder is movable in a guide, and is made 

 to pass in front of a slit which allows only a small strip of the image to 

 fall on the sensitive plate. The bellows of the camera can be drawn a 

 little away from the plate-holder, so as to permit the image to be viewed 

 from the front, it being thrown on a piece of white paper as in Nachet's 

 method. 



With regard to the choice of a room to serve as a laboratory for 

 photomicrographic work, and the setting up and adjustment of the 

 apparatus. Dr. Zeiss's very elaborate catalogue of photomicrographic 

 apparatus * should be consulted, in which valuable information is also 

 given on the nature of different sources of light and the manner of their 

 use for photomicrography, and on the special precautions required in 

 the chemical part of photomicrography. 



In photomicrographic work an objective of 75 mm. focal length has 

 been constructed which serves to take large objects (2 to 4 cm.) under a 

 magnification of ten to fifteen times. It possesses all the advantages of 

 the other apochromatic objectives. 



As illuminating apparatus, either an Abbe condenser of 1*20 to 



* C.Zeiss, ' Special -Catalog iiber Apparate fur Mikrophotographie,' 4to, Jena, 

 1888, iv. and 56 pp., 16 pis. and 9 figs. 



1889. U 



