RECENT PROGRESS IN PHYSICS. 429 



the wire retards the discharge, and in consequence of this delay there 

 is less elevation of temperature. 



His first experiment showed him, that when the length of the wire 

 in the globe Avas increased the temperature was somewhat lower. 



§ 38. Influence of the length of the wire in the thermometer. — 

 When the wire in the thermometer was made longer, a slight decrease 

 in the heating was observed, Avhich indicated a delay of the dis- 

 charge. But when the closing wire of the circuit remained in all 

 respects the same, and the temperature at diflerent parts of it was 

 examined, it appeared that the rise of temperature was independent 

 of the length of the wire. 



For instance, a piece of platinum wire in the air thermometer and 

 another equally thick and double the length in Henley's discharger 

 closing the circuit, a discharge of the battery produced a certain 

 depression. The platinum wires being now exchanged, the one in 

 the thermometer for that in the discharger, and inversely, the circuit 

 evidently remains the same in lengthy the same discharge now pro- 

 duced a double depression. The double mass of platinum was in the 

 thermometer in this case, and it had given off a double quantity of 

 heat ; hence, the temperature of the long platinum wire was the 

 same as that of the short one. 



We shall now consider more closely one of the experiments, by 

 means of which Biess proved this. The radius of the wire in the 

 thermometer was 0.036 lines; its length 59.7 lines. The diameter 

 of the wire in the discharger was 0.058 ; its length 100.4 lines. A 

 series of experiments were made with different numbers of jars and 

 variable charges, which gave as their result 



h = 0.91^- 

 s 



The wires were then exchanged. A similar series gave the result 



h = 0.5G^- 

 s 



If the wire last placed in the thermometer had been exactly as long 



as the other^ the depressions, according to the previous paragraphs, 



should be as the square of the diameters ; hence, the last case should 



give 



h =z 0.35^' 

 s 



This coefficient of ^^ is to the coefficient 0.56, as 1 is to 1.6. But 



the length of the second wire is nearly in the same proportion, viz :. 

 in the jDroportion of 59.7 to 100.4, or 1 to 1.67 longer. 



The depression in the second series, considering the different diam- 

 eters, is greater in proportion to the increase of length of the wire ; 

 hence, the heating of the separate pieces of wire is independent of 

 their length. 



This can be shown better when the actual temperatures of the wire 

 in the thermometer are computed. How this can be done will be 



