ARRANGEMENT OP APPARATUS, ETC. 93 



advantage ; they require the employment of electri- 

 city in its most expensive form, this places them 

 beyond the reach of ordinary individuals. 



In the first the virtual image is transformed into 

 a real one by displacing the eyepiece, so that the 

 image, formed by the objective, falls on the opposite 

 side of the ocular ; this may answer with the one 

 inch and lower powers, but with higher powers the 

 light is so much diminished by the interposition of 

 four surfaces of glass between the objective and 

 image, that focussing becomes impossible. 



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 reminds us of a 

 person trying 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 of our Parisian 

 brethren are possible, as according to M. Tisandier 

 the highest magnification was eight hundred dia- 

 metres. 



It has been the custom with some microscopists 



