PIERCE. — THE COOPER HEWITT MERCURY INTERRUPTER. 405 



time through the known resistance and the interrupter in series. Since 

 the heating of both resistances was produced by the same current, the 



Figure IX. Calorimeter A. 



heat developed in the two calorimeters was proportional to their 

 respective resistances. The calorimeters are shown in Figures IX and 

 X. Figure IX is the calorimeter about the mercury interrupter (calori- 



Figore X. Calorimeter 15. 



meter " A "). In its construction a glass bell-jar was put down over the 

 interrupter and cemented with fish-glue and plaster of Paris to a thick 

 glass plate provided with two holes, through which the leads to the 



