ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 841 



glass, thus facilitating the adjustment of the illumination, the ar- 

 rangement of the object, &c. This consists of a rectangular box 

 containing a total reflecting prism, which can be raised or lowered 

 by rack and pinion. In the former case the rays will pass to the 

 camera, and in the latter are reflected upwards through the sub- 

 sidiary body-tube. 



The projection apparatus consists of a substantial wooden base, 

 having grooved flanges near the edges on which a bellows camera 



B, extensible to upwards of 6 feet in length, is fitted to slide 

 smoothly. 



The Microscope is placed at the free end of the base and in a 

 horizontal position ; the body-tube is then connected with the front 

 of the camera by adapter-tubes of special construction, by which the 

 focusing movements of the Microscope are not interfered with, and at 

 the same time all extraneous light is shut out at the junction. The 

 milled head of the fine-adjustment screw is provided with a groove in 

 which travels a cord connecting it with a grooved wheel A, to which 

 a rod F D (jointed at D) is attached, so that the focusing can be 

 actuated by the milled head at F, i. e. from the extreme length of 

 the camera. 



For the general class of photo-micrographic work the camera is 

 not required to be more than about half the total length of its 

 extension ; to reduce it, the end B is slid forward on the base within 



C, the focusing rod is divided at D, the portion F D being removed, 

 together with the pillar support below F, and the hinge C then 

 permits the tail-piece of the base to be folded beneath the front part, 

 and fixed by hooks at either side. 



For focusing, the image is received on the ground glass and 

 viewed in the usual manner, or a sheet of white cardboard is sub- 

 stituted for the ground glass and the image is viewed through the 

 opening at the side V. 



This plan of substituting a piece of white paper for the ground 

 glass is one that is very little used in England. It was, we believe, 

 originally suggested by M. Moitessier,* and was applied in the first 

 instance to a vertical camera and Microscope where the height of the 

 ground glass above the stage rendered it difficult to manipulate, but 

 by adding the box at the end of the bellows, the observer was able to 

 focus from the side, looking up at the image, and also to dispense with 

 the equally inconvenient use, in M. Moitessier's opinion, of long rods 

 or similar arrangements for focusing. In his view, also, paper is 

 decidedly preferable to ground glass, " the grain of which gives rise 

 to diffraction phenomena, which are extremely objectionable, and 

 which often prevent the proper focusing of delicate objects." " With 

 the paper the image will always be much sharper than when seen 

 after transmission through ground glass, and the adjustment for focus 

 can be made much more precisely and conveniently." 



* A. Moitessier, ' La Photographie appliquc'e aux recherches luierographiques ' 

 1866, pp. 128-9. 



