OF ARTS AND SCIENCES. 491 



i? = a (1 -|- .00503 6), 



6 being the temperature. 



If then Rq be the initial resistance of the strip, and R^ the resist- 

 ance after the passage of the current, 



R, = a{lJr^^\ 



R^ = a{\ + ^e,), 



and the rise in temperature is 



^1 ^0 



6y_ ^0 



a^ 



If w be the weight of the strip, and s its specific heat, the quantity of 

 heat imparted to it by the current, is 



h = .,s(e,-e,) = --^SE^. (1.) 



But if Q is the quantity of electricity transmitted, and E the difference 

 of potential between the ends of the strip, 



Jh= QE, 



where /is the mechanical equivalent of heat. "We have 



« = §W^2sto|-, (2.) 



where a is the first swing of the needle of the ballistic galvanometer, 

 G the galvanometer constant, T the period of a single vibration of the 

 needle, and i^the horizontal component of the earth's magnetic force. 

 G was determined by comparison of the deflections on the scale of the 

 ballistic galvanometer with the readings of a tangent galvanometer 

 whose constant was calculated, included in the same circuit. In the 



experiments, 2 sin — was considered as proportional to S, the deflec- 

 tion on the scale, and the value of (? for 5 = 1 cm. was found to be 

 7G9.4. A shunt was used with the galvanometer, so that the value of 



r 4- S 

 Q above given is to be multiplied by — - — , r being the resistance of 



o 



the galvanometer, and S that of the shunt. 



