ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 



503 



Fig. 88, 



as flickering cannot be avoided when an automatic regulator is 

 used. 



The general arrangement of the instrument is shown in fig. 88. 

 It stands on a table 96 cm. high, running on wheels, so as to be 

 readily movable. The case 

 (with wooden sides) in- 

 closing the carbons is 90 

 cm. high by 74 cm. deep 

 by 45 cm. wide. It is pur- 

 posely made large, to pre- 

 vent the sides getting too 

 hot, and to allow of the 

 carbons being some dis- 

 tance from the lenses. The 

 wooden parts are also lined 

 with asbestos. 



The carbons can be 

 inclined and also moved 

 in three directions by the 

 three milled heads at B, 

 C, and D ; B raising or 

 lowering them, C moving 

 them from right to left, 

 and D backwards or for- 

 wards. The regulator is 

 at A, turning a rod with 

 differential screws, so that 

 the upper carbon moves 

 twice the distance of the lower to compensate for the difference in the 

 rate of consumj^tion. 



The special feature of the optical part (fig. 89) is that between the 

 two plano-convex condensing lenses L and the stage D is interposed 



Fig. 89. 



a conical reservoir R, 30 cm. long, filled with water, to cool the rays 

 from the lamp. It is filled by the tube at T, those at T' T' allowing 

 the air to escape. Experiments proved that practically nothing was 



