662 



LABORATORY KXERCISES 



Fig. 236, when extended. Correct focus is determined by the observation of the 

 image upon a paper surface in place of the usual ground glass. 



Fig. 236. — Edinger's drawing apparatus with attachment for photo-micrography. 



The following tables have been prepared with the view of simplifying the use of 

 the apparatus as much as possible, and the best results can only be obtained when 



