490 Magnetic Properties of Iron at High Temperatures. 



Drude is 4*25°, the theoretical value being 2'972°. When it is borne 

 in mind that the value of the magneto-optic constant derived from 

 reflection experiments has here been applied to test experiments on 

 transmission through films, with results not only of the same order 

 of magnitude, but identical within the limits of uncertainty of the 

 intensity of magnetisation, the agreement must be considered as a 

 Very satisfactory vindication both of the theory and of the 

 experiments. 



9. It is to be noticed that, as b u b 2) 6 3 are necessarily real, the 

 imaginary part of C e ix must be entirely accounted for by the Hall 

 effect. Hence the present theory involves the supposition that the 

 Hall effect is very much greater for exceedingly rapidly alternating 

 currents than for steady ones. There is nothing unnatural in this 

 supposition, which may be compared with the fact discovered by 

 Maxwell, that the ordinary coefficients of conductivity are very much 

 smaller in the optical circumstances. 



" Magnetic Properties of Iron at High Temperatures." By 

 J. Hopkinson, D.Sc.j F.R.S. Received June 10,— Read 

 June 17, 1897. 



The present note is for the purpose of correcting two points in my 

 paper in the ' Philosophical Transactions,' A, vol. 180. 



First. — I was of opinion that my experiments showed that heating 

 iron above its critical point did not entirely destroy the effects of pre- 

 vious magnetisation. Recent experiments I have made do not confirm 

 this opinion. I would therefore wish to delete the following sentences 

 in which the matter is referred to, viz. : — Page 414, lines 12 and 13 ; 

 the first paragraph on page 454 ; the first two lines on page 455 ; the 

 first paragraph on page 457 ; and from the words " two things " on 

 line 5 to the word " second " on the same page. Also in the 

 ' Proceedings of the Royal Society,' vol. 45, page 321, strike out the 

 two paragraphs at the top of the page. 



Second. — I have since been unable to obtain so great recalescence 

 with approximately pure iron as is shown in Curve XXXIX, and can 

 only conclude that I must have been in error as to the composition of 

 the sample examined. I therefore wish in the last paragraph of the 

 paper to speak of the sample as of unknown composition ; to strike 

 out the words " This shows why soft iron apparently does not 

 recalesce "; to substitute "this" for "the" and strike out " of the 

 soft iron " in the last line. 



I also take the opportunity of correcting an error in the joint paper 

 of myself and Mi . Wilson, vol. 189, pages 109 — 136. Delete the four 



