Magnetic Properties of Iron and Nickel. 367 



These experiments, I think, throw some light on the meaning 

 of the critical temperature, and make it unlikely that it is 

 due to a chemical or allotropic modification of the metal. 



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(9) Grerosa and Finzi"^ were among the earliest to make 

 experiments on the reduction of hysteresis by alternating- 

 current methods, and they showed that the curves so ob- 

 tained can be fairly well represented by Frolich's equation. 

 This equation may be put in the form 



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where T is the limit of magnetic intensity and P is a 

 constant. Reducing the observations of Table I. by [the 



* Rendiconti del Reale Istituto Lombardo, serie ii. vol. xxiv. p. 677 

 (1891). 



