156 Dr. J. Kerr's Electro-optic 



thick with a square space worked out of it as shown iu the 

 fitmre. In contact with this frame, and covering its two faces, 

 are two panes of thin plate glass, which are kept closely and 

 firmly united to the frame by a small metallic press. The 

 conductors in the cell are two balls of brass, electroplated with 

 platinum, and attached each to a stiff wire, which passes 

 upwards through an insulating tube of gh 



These tubes 



are supported by a stand (shown in the figure). The cell and 

 stand are placed on an iron tripod, and enveloped by a wide 

 muffle of sheet iron, with an aperture at the top for the long 

 conductor, and two apertures at the sides for transmission of 

 the light. Under the floor of the tripod is an Argand gas- 

 burner, which supplies a current of hot air to the interior of 

 the muffle. 



In the course of some preliminary experiments on the fats 

 and waxes, the fusion-cell was found to be not nearly so deli- 

 cate as the plate cell, both instruments working under ordinary 

 conditions — the former at high temperatures, the latter at the 



