

Strong Fields at Different Temperatures. 303 



of a hyperbola towards its asymptote P Q will be very nearly 

 I P tangentially produced. These curves of course have 

 nothing to do with those representing the permeability, 

 /* = funct. (290) which have been shown by Messrs. Ewing 

 and Low to tend towards the asymptote /* = 1, for 25'ssco . 



§ 16. The general conclusions of these physicists are 

 entirely corroborated by the present experiments, conducted 

 on altogether different lines, I believe all doubts, that have 

 occasionally arisen as to the existence of a limit of Magnetiza- 

 tion, will thereby be dissipated. In fact this quantity appears 

 about to regain its physical importance, which has lately been 

 perhaps too much transferred to Induction. This I will 

 now endeavour to show, without thereby in the least wishing 

 to contest the great advantages of induction in the mathe- 

 matical theory, as well as in the practical applications of 

 electromagnetism . 



In 1842 the late James Prescott Joule * enunciated the 

 law that the elongation of unstrained iron is proportional to 

 the square of the magnetization applied. The same has 

 recently been shown by M. Goldhammer to hold for the 

 decrease of electric conductivity f ; and it can hardly be 

 doubted that thermal conductivity varies in the same manner. 



I have shown the optical rotation to be entirely dependent 

 on and directly proportional to the magnetization on reflexion 

 as well as on transmission (loc. cit. § 23, and Phil. Mag. JSTov. 

 1887). Hall's effect probably follows the latter law f, and it 

 is natural to suppose that the three analogous phenomena 

 discovered by Messrs. v. Ettingshausen and Nernst will prove 

 no exceptions. 



§ 17. I therefore entirely agree with M. Goldhammer, 

 where he points out the probability of this general law : — 



" Magnetization affects all physical properties of metals in 

 a way generally depending on its direction. Whenever the 

 ensuing changes are odd functions of the magnetization (both 

 simultaneously reversing their sign), they are simply propor- 

 tional to it. In the case of even functions (always having 

 the same sign) , they are proportional to its square/' 



This statement is an expansion of ideas put forth by Sir 



* Joule, Reprint of Papers, i. p. 215. 



t Goldhammer, Wied. Ann. xxxvi. p. 823 (1889) ; Proces-verbmix, 

 Paris Electr. Congress, Aug. 30, 1889. 



\ This statement, well worth safely establishing "by experiment, is 

 based on the following evidence: — 1. By Hall, curve for Ni, Phil. Mao;. 

 [5] xii. p. 166 (1881) ; 2. Residual effect in steel, Phil. Mag. [5] xix. 

 p. 419 (1885) ; 3. Behaviour of conducting strips of various thicknesses, 

 tSillim. Journ. [3] xxxvi. p. 131 (1888) ; 4. By v. Ettingshausen and 

 Nernst, table for Co and Ni, Wien. Per, xciv. 2. pp. 585, 587 ^1886). 



