104 ARRANGEMENT OF APPARATUS. 



The second method due to M. Vogel, consists in 

 placing a short focus photo lens, as well as the 

 ocular, between the objective and image. This 

 method is evidently worse than the first, as we have 

 eight fresh surfaces interposed. It is an endeavour 

 to do two things at the same time, which are better 

 done separately. 



In the third and last a considerable deviation from 

 the others is noticeable. The ocular being removed, 

 a short focus carte lens is substituted and the whole 

 apparatus is placed in the horizontal position. This 

 improves the illumination as the mirror is not re- 

 quired to reflect light on the object. The same ob- 

 jections, however, hold good with regard to this. But 

 if a sufficiently strong light can be obtained, we are 

 confident that results exceeding those obtained by 

 M. Tisandier are possible, as according to him the 

 highest magnification was eight hundred diameters. 



It has been the custom with some microscopists 

 when increased magnification is required to place a 

 concave, and we believe sometimes a convex lens, 

 between the objective and focussing screen. Mr. 

 Woodward was the first to suggest this practice ; it 

 is not to be recommended, as the increased mag- 

 nification is more easily obtained by enlarging the 

 negative; besides, any combination above the objec- 

 tive impairs the image. It is our firm conviction that 

 nothing has been such an obstacle to the practice of 

 Photo-micrography, as the failures consequent on 

 allowing the eyepiece to remain in its usual position. 



