RECENT PROGRESS IN PHYSICS. 



425 



that the excess of the inner coating, acting through the glass upon 

 what surrounds it, attracts the opposite electricity towards the outer 

 coating, so that it remains latent there, and the passage between the 

 knobs of the spark micrometer is consequently hindered. This ex- 

 planation serves also for the successive discharge at the striking dis- 

 tance. 



§36. Heating of the connecting wire op the electrical battery. — 

 For experiments on the heating of thin wires by the discharge of the 

 battery, Biess used Harris' arrangement of an air thermometer, 

 through the large globe of which the wire was stretched. The tube 

 of the thermometer, narrow in comparison with the globe, was turned 

 obliquely downwards and ended in a wider position, so that a small 

 quantity of colored liquid there could penetrate the tube. 



The scale of the thermometer was divided into lines. The instru- 

 ment is represented in fig. 51. 



Fiff. 51. 



TheVire, and consequently the air in the globe, being heated by 

 the discharge, the liquid in the tube is drivea back. The depression 

 of the column of liquid expressed in lines, is considered as the mea- 

 sure of the temperature. 



A more precise description of this air thermometer will be given 

 hereafter. 



The results of an experimental series, with a platinum wire 0.0547 

 lines thick, are collected in the following table : 



