118 SUMMARY OF CUERENT RESEARCHES RELATINa TO 



The Briicke lens consists of two achromatic objective lenses and 

 a concave eye-lens. The objective lenses can be moved apart or 

 brought nearer to one another by turning the ring E. In the same 

 way the eye-lens can bo placed at various distances from the objective 

 by pushing the tube N up or down. This tube is so sprung in the 

 inner fastening that by a somewhat firm pressing together of the 

 two knobs Tc, the friction of the two tubes is lessened and an easy 

 and smooth movement is obtained. For very low powers the lower 

 objective lens can be removed. By this combination and also two 

 stronger eye-pieces all gradations of power, in the given limits, can be 

 obtained. The extent of the field of view is in inverse ratio to the 

 power within the limits of 65 to 7 mm. 



For convenient drawing a camera lucida is attached, which like 

 Zeiss's allows the drawing surface to be inclined about 22° to the 

 table. On turning the ring E, or on moving the 

 Fig. 15. tube to alter the power the camera always remains 



in the same position with regard to the ocular and 

 the drawing surface, which is claimed to be "an 

 advantage not to be undervalued, and not considered 

 in many instruments." 



In order to use the instrument for dissecting 

 there are hand-rests, made to be easily removed. 

 They consist of two hollow boxes (fig. 14) about 2/3 

 the height of the stage. They are attached by the 

 button-headed screws c to the foot of the instru- 

 ment, being inserted in the holes c^ and Cg 

 (fig. 13) and the hinged tops can be set at different 

 inclinations by the support and rack. 



Zeiss's Micrometer Eye-piece. — This (fig. 15) 

 is noticeable for the manner in which the micro- 

 meter disk is inserted. The eye-piece divides a 

 little below the middle of its length, and has an 

 additional piece between the upper and lower portions to which they 

 are screwed. In this the micrometer disk is placed. The eye-lens 

 is also in a sliding tube for adjustment to different sights. 



Bulloch's Objective Attachment. — Mr. W. H. Bulloch has de- 

 vised the objective-attachment shown in figs. 16 and 17. A is the 

 nose-piece adapter to screw on the Microscope, and B is the 

 ring, provided with three wedge-shaped studs, to be screwed on 

 the objective. Three slots are cut in the body of the lower 

 cylinder of the nose-piece A, and three similar slots in the inward 

 projecting rim of a rotating collar. When the two sets of slots 

 correspond, the ring B, with the objective attached, can be slid 

 into the nose-piece, and then the studs are locked firmly by a slight 

 turn of the rotating collar, which causes its projecting rim to slide 

 over the outer halves of the studs. By reason of the wedge form 

 given to the studs, the collar can be made to press down upon them 

 with more or less force. The objective cannot be removed from the 

 nose-piece until the rotating collar is turned back to the normal posi- 

 tion, releasing the studs. 



