158 HOW TO SEE WITH THE MICROSCOPE. 



difficulties. It is best suited to thin and flat objects ; 

 with those that are thick and irregular, distortion is 

 unavoidable. Although specially designed as a dark 



ground illuminator, good effects can with care [and by 

 the use of suitable objectives], be obtained lor such ob- 

 jects as difficult diatoms, in balsam or dammar. But 

 the effect is that of very oblique transparent illumination" 

 We have preferred to give the above description from 



