CH. VIII.-] PHOTO-MICROGRAPHY. 187 



Fig. 143. Walmsley's Improved Photo-Micrographic Camera. In this figure is 

 shown an excellent form of photo-micrographic camera for use with a horizontal 

 microscope. It has the advantage of the possibility of a very long bellows or a 

 shorter one as the need of the specal case demands. It is arranged for photo-mi- 

 crographic work with the microscope or a wide angled objective or for copying and 

 slightly enlarging or diminishing, drawing, etc., with an ordinary photographic 

 objective. It is also arranged for making lantern slides. A very simple arrange- 

 ment has been adopted for focusing when the bellows is pulled out so far that one 

 cannot reach the fine adjustment, and it works with great smoothness. "A groove 

 is turned in the periphery of the fine adjustment screw, around which a small cord 

 is passed, and carried through a succession of screw-eyes on either side of the base- 

 board to the rear, where a couple of small leaden weights are attached to its ends, 

 thus keeping the cord taut. A very slight pull on either side, whilst the eye is 

 fixed upon the image on the screen, suffices to adjust the focus with the utmost 

 exactness. If preferred, a rod running the entire length of the camera-bed, and 

 terminating at the rear end with a milled head, whilst on the other is a grooved 

 pulley, carrying a cord or belt which also passes around the groove in the milled 

 head of the fine adjustment, may be substituted for the cord and weights. This 

 arrangement \_shown in the figure] is more costly, and probably no better in actual 

 service than that with the cord and weights." (From Mr. Walmsley.) 



I 325. Work Room. — It is almost self-evident that the camera must be in some 

 place free from vibration. Frequently a basement room where the camera table 

 may rest directly on the ground or on a pier is an excellent situation. Such a sit- 

 uation is almost necessary for the best work with high powers. For those living 

 in cities, a time must also be chosen when there are no heavy vehicles moving in 

 the streets. For less difficult work an ordinary room in a quiet part of the house 

 or laboratory building will suffice. 



§ 326. Arrangement and Position of the Camera and the Microscope. — For the 

 greater number of photo-micrographs, a horizontal camera and microscope are to 

 be preferred as one may then vary the length of the bellows at will and still pre- 

 serve steadiness (Fig. 143). For some specimens, however, it is necessary to keep 

 the microscope in a vertical position, hence to photograph, the camera must also 

 be vertical. Very excellent arrangements were perfected long ago, especially by 

 the French. (See Moitessier). 



Vertical photo-micrographic cameras are now very commonly made, and by some 

 firms only vertical cameras are produced. They are exceedingly convenient, and 

 do not require so great a disarrangement of the microscope to make the picture. 

 Van Heurck advises their use, then whenever a structure is shown with especial 

 excellence it is photographed immediately. The variation in size of the picture is 

 obtained by the objective and the projection ocular rather than by length of bel- 

 lows (see below). (Fig. 144). It must not be forgotten, however, that penetration 

 varies inversely as the square of the power, and only inversely as the numerical 

 aperture ($ 29), consequently there is a real advantage in using a low power of 

 great aperture and a long bellows rather than an objective of higher power with a 

 shorter bellows. (See Carpenter-Dallinger, pp. 318-319). 



\ 327. Microscope. — For convenience and rapidity of work a microscope with 

 mechanical stage is very desirable. It is also an advantage to have a tube of large 

 diameter so that the field will not be too greatly restricted. In some microscopes 



