Magnetostriction of Steel, Nickel, Cobalt, and Nickel-Steels. 45 



e being expressed in electromagnetic units. As the velocity ' 

 increases m 2 increases ; hence m, what is usually taken to be 

 the mass o£ an ion consisting of the ordinary mechanical 

 mass together with the apparent mass due to the moving 

 charge, is greater than m 2 . 



Hence 2 e 2 



m> 



3 



P' 





P> 



2 



e? 





> 



4 



3 



io- 



13 



i. e. 



The value therefore that we have calculated for p lies 

 between the limits that can be assigned to it in other ways. 



The experiments described in this paper were carried out 

 in the Cavendish Laboratory, and I have much pleasure in 

 expressing my gratitude and best thanks to Professor 

 Thomson for many suggestions and kindly advice given 

 during the progress of the work. 



IV. On the Magnetostriction of Steel, Nickel, Cobalt, and 

 Nickel-Steels. By H. Nagaoka, Professor of Physics, and 

 K. Honda, Lecturer in Physics, Imperial University, Tokyo *. 



§ 1. Introduction. 



§ 2. M.ignetization of Steel, Nickel, Cobalt, and Nickel-Steels. 

 § 3. Change of Length by Magnetization in (a) Steel ovoid, (5) Nickel 

 ovoid, (c) Cobalt (cast and annealed) ovoids, (d) Reversible 

 Nickel ovoids containing 46, 30, 29, 25 per cent, of Nickel, 

 (e) Reversible Nickel-Steel wires containing 46, 35 per cent, of 

 Nickel in low fields. 

 § 4. Effect of Mechanically Elongating Cobalt and Nickel-Steels on 

 Magnetization, and the reciprocal relations with the change of 

 length. 

 § 5. Change of Volume by Magnetization in Steel, Nickel, Cobalt, 



and Nickel-Steel ovoids. 

 § 6. Wiedemann Effect in Iron, Nickel, and Nickel-Steel wires. 



(«) Twist produced by the interaction of circular and longitu- 

 dinal magnetizations, (b) circular magnetization produced 

 by twisting a longitudinally magnetized wire, (c) longi- 

 tudinal magnetization produced by twisting a circularly 

 magnetized wire, (d) application of KirchhofFs theory to 

 "Wiedemann effect and reciprocal relations. 

 § 7. Summary of the Results. 



§ 1. Introduction. 



IN the course of our researches on the magnetostriction of 

 different ferromagnetic bodies, questions of various cha- 

 racter presented themselves, both with regard to the method 

 * Communicated by the Authors. 



