ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



321 



imposes on condensers have been carefully borne in mind. Fig. 42 

 shows the path of the light-beams issuing from the condensers into a 

 fluorescent uranuim glass. The good spherical and chromatic correction 



l.sxVk'JvV.W.'.'s'JS 



' -.~^'- -sVkVs^'.tkvkvk ' Wiy 



Fig. 40, 



Fig. 41. 



and the satisfaction of the sine-condition furnish such an illumination 

 of the object in the dark ground that the images appear undistorted, 



Fig. 42. 



colour-clean, and free from disturbing reflexions and refractions. The 

 dark ground is obtained by placing a central diaphragm in the usual 

 way on the carrier of the iris. Fig. 41 shows the ray-paths through the 



