ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



103 



If the apparatus is to be used for megascopic projection the right-hand 

 side wall is provided with an opening into which the plate with mirror 

 and objectives is inserted. This opening is also covered with a lid when 

 the apparatus is out of use. 



Instead of a glass condenser a hollow parabolic mirror is used. This 

 arrangement offers great advantages. The light-source is an arc lamp 

 with regulators and automatic control. It takes a current strength up 

 to 40 amperes with a slightly adjustable tension of 65 volts. The carbons 



v^ 



Fig. 21. 



are horizontal, the carbon of the positive being turned towards the mirror 

 in the lamp chamber. The mirror can be moved forwards and backwards 

 by means of a pole-shaped handle projecting through the box ; in this 

 way a greater or less convergence is communicated to the l)eam of rays. 

 The reflector is vertically adjustable on a strong fork. For episcopic 

 projection it is sloped about 18° upwards ; for diascopic projection al)out 

 15° downwards. In both cases a catch gives the right position. A 

 similar contrivance also secures the true horizontal adjustment as required 

 for microscopic and megascopic projections. 



