Permanent Magnets. 



191 



In his paper on magnetic distribution. Prof. Rowland gives 

 the following formula for the linear distribution in a magnet 



§ (# 



in which R is the resistance of unit length of the rod, R r is the 

 resistance of the medium along unit length of the rod, 2h is 

 the length of the magnet, x is the distance from the center of 



the magnet, and r=4 



A B 



At li° C. the formula for magnet A may be written 



at 99°-5 C, 



4-A=16' 



4ttA=:161 



3 0-125«r_ e -0-125,r 



e 0-1256 + e 



0-1256 



e 0-i242.r_ e -0-1242.r 



0-12426 . - 0-12426 

 e -f-e 



III. Discussion of Results. 



The first series of experiments shows that the proportional 

 change in magnetic moment due to change in temperature is 

 greater for short than for long magnets ; and that the magnet 

 having the greater intensitv of magnetization suffers the less 

 proportional change. This last result is not in agreement with 

 the observations of Wiedemann given on page 180. A little 

 consideration will show, however, that Wiedemann's method 

 cannot be relied upon to give accurate results for the change 

 in magnetic moment. He placed a magnetometer needle before 

 the magnet and observed the deflection of the needle for two 

 temperatures of the magnet. If the center of magnetic attrac- 

 tion had remained at the same point of the magnet during the 



