OP ARTS AND SCIENCES. 



195 



Both of the nickel curves increase in steepness at first, but attain a 

 maximum height between 150° and 200° and then fall very rapidly. 



It is well known that certain marked chancres occur in two of the 

 physical properties of nickel in the region of 200° C. One of these is 

 a thermo-electric effect, a reversal of the so called " specific heat of 

 electricity " in the substance ; the other is a great diminution of the 

 magnetic permeability. 



The "specific heat of electricity " is supposed to be nearly constant 

 at temperatures below 200° C, and to suffer a second reversal of sign 

 at a point somewhat above 300° C, in which two particulars it ap- 

 pears to have no connection with the course of the Hall effect at 

 the same temperatures. 



150° 200° 

 Figure 2. 



In Figure 2 several curves are given to illustrate the changes of 

 magnetic permeability, with unchanging magnetic induction, which 

 nickel suffers with rise of temperature. Curves D, E, F, and G are 

 plotted with data taken from the curves given by Mr. C. A. Perkins 

 in the American Journal of Science, Vol. XXX. p. 218, to show how 

 the magnetic properties of very pure rolled nickel are affected by 

 changes of temperature. None of the curves given by IMr. Perkins 



