440 RECENT PROGRESS IN PHYSICS. 



By lengthening the circuit the rise of temperature is dimin- 

 ished. If, instead of metallic wire, a piece of moistened wood, or a 

 glass tuhe filled with water, be introduced, the most powerful charges 

 of the battery are not al^le to produce a depression of even 0.1 line. 

 Here the discharge of the battery is no longer instantaneous, as with 

 the interposition of the longest copper wire ; it requires a perceptible 

 time. Hence it is inferred that a difference might be observed in the 

 time of discharge when a long or short wire was used if we were 

 endowed with keener senses. The heating of the platinum wire in 

 the thermometer appears to be in simple inverse ratio with the time 

 during which the discharge lasts, A temperature a being observed, 

 while a certain quantity of electricity of a given density is discharged 

 in the time 1, the time of discharge will be prolonged by h ?., if a wire 

 of the length X is introduced ; and the temperature is now 



a 

 h = 



l-}-hX 



or the heating of a wire hy the discharge of on electrical battery is in- 

 versely proportional to the duratien of the discharge ; the duration of 

 the discharge is prolonged hy lengthening the ivire of the circicit by a 

 time luhich is proportional to the length of the loire added. 



§ 45. Influence of the thickne,?s op tue connecting wire upon its 

 TEMPERATURE. — In Order to investigate the influence of the thickness 

 of the connecting wire Eiess removed the interposed copper wire 

 which he had used in the previous experiments, and in its stead 

 placed, in succession, platinum wires of various dimensions between 

 the arms oi^ Henley's discharger. The result was that the thermome- 

 ter indicated temperatures as much lower, as the platinum wires of 

 like lengths were thinner. The data thus obtained admit of the 

 formula 



Expressed in words this 



The heating of a wire hy electrical discharge is inversely proportional 

 to the duration of the discharge ; hy interposing homogenous quires the 

 discharge is prolonged hy a time which is directly 2y^opo7'iioncd to the 

 length of the interposed ivire, and invei^sely prc^ortional to its section. 



§ 46. Temperature in the :\iain conductor of a branched circuit. 

 Having determined how much retardation of discharge is produced by 

 a wire a introduced into the circuit, the value of retardation by a 

 second wire /9 is obtained in like manner ; and it may be asked now 

 how much retardation is produced by introducing both wires at the 

 same time as branches in the circuit. 



The annexed diagrams may serve to show more clearly how this 

 question is to be understood. 



