848 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



A stronger eye-piece would give a larger image, as at F F 4 . 

 The lower part of the tube, which carries at L the incandescent 

 electric light, is shown in perspective as well as in section. 



Cramer's Movable Stage.* — Dr. C. Cramer's movable stage (figs. 

 170 and 171), is described with a wealth of detail which seems in- 

 separable from the descriptions of similar apparatus by Continental 

 writers. It fits over the fixed stage, and acts as a finder. 



Fig. 170 shows the apparatus as seen from above. It is so fitted to 

 the stage that the screw S is at the right hand of the Microscope. 



Fig. 170 



Fig. 171. 



Fig. 171 is a section as seen from the left end. The apparatus consists 

 of a frame R of lacquered brass about 14 cm. long and 2 ■ 5 mm. 

 thick, the long sides of which are bowed out in the middle to prevent 

 any collision between the objective and the frame. The two cross- 

 pieces L' L" project over the edge of the stage, so that the apparatus 

 can be pushed forwards and backwards as required. L' is the longer 

 of the two and has a line and letter o marked on its lower end. 



This index is intended to be used in 

 conjunction with a millimeter scale 

 on the edge of the stage. The cross- 

 pieces L' and L" are not united 

 directly to the frame R, but by 

 means of two rectangular brass slips ; 

 the dotted lines sch fig. 170 show 

 their extent in horizontal projection, and fig. 171 gives them in section, 

 and shows that they slope inwards and downwards, forming a kind 

 of groove for the reception of a slide, moving parallel to the long 

 axis of the apparatus. This slide consists of a blackened brass 

 plate t not more than 1/2 mm. thick, provided in the middle with a 

 square opening, the sides of which are 24 mm. long. It is stiffened 

 with a thin blackened framework r. The long side pieces of the 

 frame r are sloped inwards so as to fit accurately in the groove. The 

 slide is therefore firmly held in its movements to and fro. According 

 as the screw S is turned one way or the other the slide t will be 

 moved to the right or the left, the extent of the movement being 

 24 mm., the width of the quadrangular central aperture. 



* Zeitschr. f. Wiss. Mikr., iii. (1SSG) pp. 5-14 (2 fi^s.). 



