In using the mi croscope with the or dinary length of body or tube—some ten or twelve in ch e s--the field or size of pic ture obtainable is of ten restricted by the marginal rays strik ing the inside of the ocular end of the tube from which they are reflected, and pro duce a confused image or foggy picture. To obviate such defect the body of the microscope is made short, and is held in position by a firm arm of brass projecting from the metal sleeve, sliding on the square rod which carries the photographic parts of the instrument. This sleeve is kept in position by a set screw most plainly seen in Fig. 341. The back end of this sleeve is also fastened by a set-screw, one of the bars carrying the bearings for the adjusting rods here after mentioned. The back bearing for these rods is attached to the wood sleeve which carries the camera part of the device. This is held in position by a winged thumb-nut seen in Fig. 338 and 339, which clamps it to a sliding tongue held to the arm carrying optical or barrel part by hinged and hooked clamp seen in Figs. 34o and 341. The approximate focus is obtained by the telescoping box, which is held in position by a thumb-nut clasping a slotted tongue of brass on top of the box, as seen in Figs. 338, 339, and 34o. On the back end of the sliding box are_hooked plate holder carriers, extensions, or such other appliances as may be required. To the side of the bed carrying the camera box are secured adjustable slats, which provide means for tightening the belts passing over the larger pulleys which they carry, as seen in Figs. 338 and 339. These long belts put in action the spool pulleys which carry shorter belts for moving the mechanical stage across, or up and down the field of the objective, as shown in all the figures. The rod
on the right hand side of the instrument carries a pulley for making the fine adjustment, as best shown in Fig. 341.
The rod on the left carries a pulley for the band passing over a grooved ring attached to collar of the objective for cover-glass adjustment. The iron stand carrying the stage, sub stage, mirror, etc., is attached to the bar supporting camera-box and other parts by a strong screw worked by a short lever, as seen in Fig. 338. The head of this lever-screw serves another important purpose in preventing injury of objective or cover-glass by meeting the head of a long screw passing through the vertical arm which supports the optical parts as shown in Fig. 338. The use of adjustable support for back of camera-box is so plainly shown in the figures as to require no written description. In conclusion, a few words regarding some of the peculiar advantages of this instrument may not here be out of place. First, the mechanical and optical parts are so constructed that any slight vibration will not throw them out of ad justment, as all are firmly attached to one center, which admits of the whole being easily put in horizontal, vertical or angular position, as the work in hand may require. All parts are adjustable' for wear, atmospheric changes, and the various classes of work. The operator, seated at the back of the camera, can manipulate the whole instrument with ease and certainty, even to the adjustment for cover-glass, and searching the field for any particular object, or selecting the most suitable for his purpose. The whole apparatus is light and compact. Size of plates used, 3i x 44. The large Bellevue instrument, on this general plan, carries plates 8 x io.