198 



CLASS DEMONSTRATIONS 



[CH. VII 



FIG. 155. Compound Microscope with triple nose-piece and objectives and 

 ocular in position. The ring below the condenser is draivn to one side. This 

 ring is for blue glass or for a central-stop to use in dark-ground illumination 

 (| /oj). In demonstrations it is a great advantage to have a fine hair in the 

 ocular as shown in Figs. 153-154. (Cut loaned by Williams, Broivn & Earle > 

 Phila.} 



