ZOOLOGY AND BOTANY, MICROSCOPY, ETC 



809 



firmly in a sleeve 2, which surrounds a slit adjustable by means of a 

 micrometer-screw 3. In this manner the image of the bright bar can be 

 made to fall sharp and clear upon the diaphragm of the Microscope- 

 condenser. The screw 4 is for centring the light-source with regard 

 to the axis of the collector. This screw raises and lowers the bright 

 bar, and thereby effects a corresponding perpendicular movement of its 

 image. A lateral movement is not necessary, for the image of the long 

 thread always covers in this direction the condenser-diaphragm, provided 

 that the height-adjustment is rightly attained. The bright bar lies in a 

 pillbox-shaped receptacle, whose under portion is shown in fig. 90 sepa- 

 rated from the upper part. In this lower part are seen the two electrodes, 



Fig. 90. 



connected by a platinum wire and secured by the small screws 5. The 

 front wall 6 of the receptacle is approximately square, and is provided 

 with a small opening opposite to the collector. A so-called parallelogram- 

 movement connects the opening with the pillar carrying the slit and 

 collector, and controls the above-mentioned vertical adjustment of the 

 light-source. The front and rear walls of the receptacle are provided 

 with ventilation openings, and the front wall has also wing-shaped 

 projections for assisting cooling-down. Between the receptacle and the 

 collector is a covering 8 for guarding the collector against radiation from 

 light-source and from receptacle. A rider 9 serves to cany the whole 

 on Zeiss' optical bench. The author also describes many of the details 

 connected with the current and with the management of the light. 



