ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



687 



The author adds some remarks as to the special objectives necessary 

 for a Microscope with telescopic eye-pieces. It must not be expected, 

 he says, that proper images can be obtained with objectives which are 

 suitable for ordinary Microscopes ; for not only does the bisecting of 

 the rays influence the quality of the images, but the course of the rays is 

 quite different. We must have, therefore, objectives specially corrected 

 for parallel pencils. The lenses of an ordinary objective are placed 

 closer together, as though to suit very thick cover-glass. The object 

 is of course at the focus of the objective instead of being outside it, as 

 in the ordinary compound Microscope, or within it, as in the simple. 

 The results already obtained justify, it is said, the hope that the mode- 

 rate magnifying powers hitherto reached (scarcely above 200) can be 

 considerably increased. With a power of 120 the striae on the scales of 

 Hipparchia Janira were well seen, with an eye-piece power equal only 

 to the weakest now used ; with stronger eye-pieces the power could 

 easily be doubled. 



Fig. 76. 



Fig. 77. 



Holmes's Isophotal Binocular Microscope. — This is shown in fig. 76. 

 The optical principle of the instrument was described at p. 870 of 

 Vol. III. (1880). A peculiarity of the mechanical arrangement is that 

 the tubes are made to rock from side to side on a socket. The object 



