HISTORY OF THE MICROSCOPE. 



15 



in altitude and azimuth. Fig. 3a shows the instrument 

 inclined at about the usual position for working with 

 central lights ; and fig. 3& shows the section at the 

 lowest point in the horizontal position and with the 

 sub-stage removed. The principal movements of this 

 improved form of 

 B-oss-Wenham mi- 

 croscope were de- 

 scribed in the Jour- 

 nal of the Royal 

 Microscopical Soci- 

 ety, April, 1882, p. 

 255. Briefly stated, 

 the leading princi- 

 ple followed in the 

 construction of the 

 stand is that when 

 it is inclined back- 

 wards, or turned 

 laterally or horizon- 

 tally, or rotated on 

 the base-plate, a 

 pencil of light from 

 a fixed source will 

 always reach the 

 object, all the move- 

 ments, whether sep- 

 arate or combined, 

 radiating from the. 

 object or the pro- 

 longation of its axis 

 as a centre. 



The stage rotates 

 completely and is 

 a modification of 

 Tolles', in which 

 the rectangular motions are effected by milled heads 

 acting on the surface and entirely within the circum- 

 ference. This instrument, which is mounted on the 

 Ross-Zentmayer system, will be the microscope of the 

 future. 



FIG. 3&. 

 The Ross- Wenham Microscope. 



