574 



Dr. J. Larmor on the 



Nickel-Steel 24*04 per cent, 



*=_2°-0C. 



^=-64°-0C. 



^=-96°-0O. 



H. 



T xl ° 6 - 



H. 



fxlO, 



H. 



*X1C. 



40 9 

 124-4 



266 

 4(53 



01 



0-2 

 0-6 

 11 



43-5 

 114-0 

 217-3 

 402 



O-o 



20 

 3-7 

 66 



20-5 



44-2 



125-4 



216 8 



318 



412 



o-i 



1-0 

 34 

 5-6 

 7-7 

 9-3 



From these numbers, we find a parallelism between the 

 change of magnetization and that o£ the length-change. In 

 weak fields, the change of length gradually increases as the 

 temperature falls till it reaches a maximum, and then 

 decreases. As the field becomes stronger the maximum 

 elongation is displaced in lower temperatures, and at last 

 vanishes. These changes are common to nickel- steels o£ 

 percentages higher than 28 '32 per cent. ; for percentages 

 lower than 26'64 per cent, the elongation for a const nit 

 field at first increases gradually and then rapidly, soon 

 approaching an asymptotic value as the temperature falls. 



[To be continued.] 



LXIII. On the Constitution of Natural Radiation. 

 By J. Larmok, F.R.S. * 



THE recent paper by Lord Rayleigh on " The Origin of 

 the Prismatic Colours " t recurs to fundamental and 

 delicate points in the philosophy of Optics, first effectively 

 expounded by himself in 1881 and the following years {, on 

 which 1 desire to offer some observations ; especially as the 

 mode of exposition of the dispersive action of a prism which 

 was adopted by me several years ago § has been the subject 

 of criticism in the papers by Schuster and Ames, to which 

 Lord Rayleigh refers at the beginning of his paper. 



The first part of the following remarks would doubtless 

 bear condensation, as the full force of Lord Rayleigh's 

 comparison of the dispersion problem with that of a travelling 

 maintained source had not been grasped when they were 

 written ; but in a subject which so largely turns on the mode 

 of expression, condensation might involve obscurity. There 



* Communicated by the Author. 

 t Phil. Mao-. Oct. 1905, p. 401 . 



X Of. especially ' Wave Theory' § 7, Ency. Brit. 1888; Scientific Papers, 

 vol. iii. 



§ ' /Ether and Matter,' 1900, chap. xv. 



