3G Messrs. K. Honda and T. Terada on the Change of 

 AVe hope to apply before long tlie method of § 128 to 



calculate, by aid of the formula ' dqyjr(cV — vq, z, t — q), the 



Jo 

 initiation and continued growth of Canal Ship-waves, due to 

 the sudden commencement and continued application of a 

 moving, steady surface-pressure, ^(a.-, 1, 0). We hope also 

 to apply (139) of the present paper to the fulfilment of my 

 old promise (§ 30, June 20, 1904, R.S.E,) to deal with the 

 beautifully varying procession seen circling outwards from 

 the place of a stone thrown into deep water. 



II. On the Change of Elastic Constants of Ferromagnetic 

 Substances by Magnetization. By K. Honda and T. Terada, 

 Lecturers in Physics in the Tokyo Imperial University*. 



[Plates l.-V.] 



§ 1. Introduction. 



THE elastic constant of a substance in a magnetic field 

 is here defined as the ratio of the stress applied to the 

 strain caused thereby, the magnetic force constantly acting 

 on the substance. The change of elasticity is then the dif- 

 ference of this quantity, when the magnetic field is on, and 

 when it is off. In the case of ferromagnetic substances, for 

 which the hysteresis is considerable, the change of elasticity 

 so defined may, or may not, coincide with that of the same 

 ratio when the stress is first applied and then the field. 

 However, little attention seems to have hitherto been paid to 

 this point. Thus, in many! of the experiments hitherto 

 made regarding the change of elastic constants by magneti- 

 zation, the right order of properly applying the stress and 

 the field was inverted. In some experiments J the effect of 

 tension on the magnetic elongation was observed, and the 

 change of the modulus of elasticity was deduced on the 

 assumption that the effect was due to the change of elasticity 



* Communicated "bv the Authors. 



t Guillemin, C. R. xxil pp. 264 & 432 (1«46> : J. S. Stevens & H. G. 

 Dorsey, Phys. Rev. (2) ix. p. 116 (1899) ; G. Wiedemann, Electncitiit, 

 iii. p. 796; C. Barus, Amer. Journ. xxxiv. p. 175 (1887), Phys. Rev. 

 xiii. p. 257 (1901) ; Day, ' Electrician,' xxxix. p. 480 (1897) ; J. S. 

 Stevens, Phys. Rev. (3) x. p. Ill (1900) ; K. Honda & S. Shimizu, Journ. 

 Sc. Coll., Arts. 12 & 13, vol. xvi. (1902). 



T Bock, Wied. Ann. liv. p. 442 (1895), Phil. Mag-. (5) xxxix. p. 548 

 <189o) ; K. Tangl, Ann. de Phys. vi. p. 34 (1901) ; K. Honda & S. Shimizu, 

 loc. cit. 



