320 



SUMJIARY OF CURRENT RESEARCHES RELATING TO 



Fig. 71. 



fact a triple achromatic combination (a triplet and two doublets) and 



when used without the ocular (also achro- 

 matic) the different combinations will give 

 amplifications of 15, 20, or 30 times. 

 When used with the ocular, amplifications 

 of 40, 60, and 100 can be obtained with 

 a working distance of 27, 16, and 9 mm. 

 Mr. E. M. Nelson informs us he has found 

 the power of 100 useful in finding parti- 

 cular specimens on slides, and for the 

 examination of slides such as Cole's series. 

 The field of view visible at one time is 

 small, but by moving the eye over the eye- 

 piece a considerable area can be looked 

 over. 



In this form there is no provision for 

 increasing or diminishing the power of 

 the combination as was effected in the 

 original Briicke lens,* by varying the dis- 

 tance of the ocular from the objective, a 

 device anticipated by the "objectif vari- 

 able " of C.Chevalier,f in which the lenses 

 Fig. 72. 



0* * 



M.m6£fisa J£M. 



* Si e this Journal, ii. (1882) p. 101. 



t Chevalier, C, ' Des Microscopes et de lenr usage,' 1839, p. 156 (2 figs.). 



