712 



KECOKD OF CURRENT RESEARCHES RELATING TO 



Fig. 59. 



only in tlie case of Trichince, but also for vegetable tissues. It is a 

 Microscope combined with a compressorium. The latter consists of 

 a metal ring c, wliich is pressed upon the stage by a spring /, and 

 can be released by pressing the lever d. The ring being raised, the 

 object to be examined (placed between two glass plates) is laid upon 



the stage, and the ring is 

 then allowed to descend 

 gently upon the plates. 



Schmidt and Haenscli's 

 (shown in Figs. 60 and 61) 

 also includes a combined stage 

 (E) and a compressorium (C) 

 (acted upon by two screws), 

 but has in addition a special 

 arrangement for coarse and 

 fine adjustment of focus. The 

 inner tube carrying the eye- 

 piece and objective, which 

 slides within the outer tube 

 attached to the pillar of the 

 Microscope, is provided with 

 a projecting pin which moves 

 in a slot cut obliquely in the 

 outer tube like the thread of 

 a screw, so that by rotating 

 the milled rim (B) of the inner 

 tube it is made to slowly as- 

 cend and descend as desired. 

 It is claimed * for this 

 plan that it obviates a defect 

 in centering found to exist 

 in Microscopes with the ordi- 

 nary sliding adjustment, with 

 which it constantly happens 

 that after the tube has been 

 drawn up to change the 

 " powers, a suspicious spot 



which it was desired to examine is found to have disaj^peared from 

 the field of view. The objection to the arrangement will probably be 

 found in the tendency of the tube to " run down " ; at least that was 

 found to be so in the case of an arrangement somewhat analogous 

 in principle, proposed by Mr. Fiddian some years ago. 



The second improvement claimed is the movement of the stage 

 in two rectangular directions by the lever A and rack and pinion D. 

 It is pointed out that it is impossible even for a practised micro- 

 scopist to move the object in the absence of mechanical apjiliances 

 without missing any portion of the surface. By means of a test 

 plate consisting of a photograph (a square German inch in size) of 

 the numbers 1 to 700, small enough to be clearly legible under a 

 high power, it was found that the error was as much as 30 per 

 * Sco ' Imliishie-lilaltcr,' xvi. (1879) p. 289. 



