1889.] Electrical Resistance of Iron at High temperature. 457 



quantity of heat liberated. The dotted lines in the curve show 

 the continuation of the first and second parts of the curve, the 

 horizontal distance between these approximately represents the time 

 during which the material TV as giving out heat without fall of tempe- 

 rature. After the bend in the curve the temperature is falling at the 

 rate of 0'21 C. per second. The distance between the two curves is 

 810 seconds. It follows that the heat liberated in recalescence of 

 this sample is 173 times the heat liberated when the iron falls in 

 temperature 1 C. With the same sample I have also observed an 

 ascending curve of temperature. There is in this case no reduction 

 of temperature at the point of recalescence, but there is a very 

 substantial reduction in the rate at which the temperature rises. 



V. " Electrical Resistance of Iron at a High Temperature." 

 By J. HOPKINSON. Received March 14, 1889. 



Auerbach, Callendar, and I think also Tait, have observed that the 

 temperature coefficient of electrical resistance of iron is abnormally 

 high. So far as I know no one has pushed his observations to the 

 temperature at which iron ceases to be magnetic. 



The accompanying curve shows the results of experiments made 

 upon a very soft iron wire. The abscissae are the temperatures as 

 estimated by the resistance of a copper wire, the ordi nates represent 

 the resistance of the iron wire having unit resistance at 20 C. It 



2 H 2 



