130 Messrs. A. S. Russell and F. Soddj on the 



In the case o£ nickel, the change of resistance shows a 

 tendency towards a constant minimum which is reached in a 

 field of about 24,000 c.G.s. units. For the first specimen the 

 total decrease in the value of A<£ after the maximum is 

 reached is 0*0030, and for the second specimen 0-0042. 



There is no tendency towards a constant minimum shown 

 in iron in the fields examined, the fractional change of 

 resistance steadily diminishing as the magnetic field increases. 



Comparing these results with those of Barlow, we find that 

 the diminution in the value of A(£ for nickel between the 

 field strengths 2000 c.G.s. and 18,000 c.G.s. units, is about one 

 half that observed by him. It is possible, therefore, that the 

 diminution o£ A<j) observed by him in strong fields is not 

 entirely to be accounted for by the end elements of his coil, 

 which were magnetized transversely, but was made up of the 

 decrease due to both longitudinal and transverse effects 

 acting together. 



According to the electron theory of metallic conduction as 

 given by Drude *, the change of resistance due to a longi- 

 tudinal magnetic force is proportional to the square of the 

 strength of the field in which the electrons are moving. In 

 a magnetic metal this is presumably to be identified with 

 the magnetic induction, and the change of resistance should 

 therefore be proportional to the square of the magnetic 

 induction. The results of the present experiments are thus 

 not in accordance with this form of the electron theory. 



All the above experiments were carried out in the Physical 

 Laboratory of the University College of North Wales. In 

 conclusion, I desire to express my thanks to Professor E. 

 Taylor Jones for the interest he has taken in the work, and 

 for much valuable help and advice. 



XVII. The y-JRays of Thorium and Actinium. By Alex- 

 ander S. Russell, M.A., B.Sc, and Frederick Soddy, 

 ALA., F.R.SA 



SIMILAR investigations to those described in two previous 

 papers % on the 7-rays of uranium X and radium C have 

 been carried out with the 7-rays of actinium C (or possibly it 

 may prove to be actinium D) and with the two types of 

 powerful 7-radiation in the thorium series, namely that given 



* Drude, Ami. der Phys. iii. p. 378 (1900). 

 f Communicated bv the Authors. 



% Phil. Mag. 1909 [6] xviii. p. 620: 1910, xix. p. 725. For brevity 

 these two papers will be referred to throughout as I. and II. respectively. 



