ZOOLOGY AND BOTANT, MICROSCOPY, ETC. 



237 



on by a third clamping roller which conducts the current. The carbons 

 can during the lamp-burning be extracted without previously switching 

 off the current, and then replaced by fresh ones. As in the Liliput Arc 

 Lamp a condenser lens of short focal length is used, thereby furnishing 



Fig. 35. 



Fig. 30. 



a beam of rays of very high intensity. By movement of this lens the 

 beam is rendered parallel, convergent, or divergent. This movement 

 takes place in a laterally applied groove, whereby a broad space for ven- 

 tilation is left in front, and jamming of the heated condenser tube ren- 



