492 



gram on the back side of the door is shown in Fig. 3 (A). The mica is 

 held in place by means of four pices of brass, 1.7 mm. thick and 1.5 cm. 

 wide. These pieces are screwed onto the door in such a way that they not 



K~ w 



only hold the mica in place over the window but they also form a close 

 fitting rabbeted joint of the door to the box. 



The back side of the electroscope is constructed like the front side, 

 with a mica window of the same dimensions for illumination. This side 

 may be either hinged to the box or it may be held iu place by means of 

 two little hooks. 



