224 Prof. E. Taylor Jones on most Effective Primary 



could not be detected with the experimental arrangement 

 employed. 



I wish to express my sincere thanks to Sir Ernest 

 Rutherford for bis help and advice. 



Physical Laboratory, 

 The University, Manchester. 

 July 1914. 



Note. — While these experiments were in progress, H. 

 Richardson (Proc. Roy. Soc. A. xc. p. 521, 1914) has 

 examined the secondary radiation excited in different 

 elements by the /3 rays from an inLense source containing 

 radium B and radium C. The method he used was the same 

 by which Chadwick* in 1912 had proved the existence 

 of this radiation, but the experimental arrangement was 

 more suitable to detect soft radiations. The mass ab- 

 sorption coefficient for the secondary rays excited in a large 

 number of elements has been determined in this way. 

 The values found for eleven comparatively light elements 

 (atomic weights 58"8-137'4) show the same striking resem- 

 blance with the corresponding values obtained by Barkhi for 

 the "K - " series of characteristic X rays, which has been 

 pointed out in the present note. Six heavier elements 

 (195*3-238) gave results very close to those found for 

 the " L " series of characteristic rays. The few results 

 obtained in the present investigation by using radium D and 

 radium E, in addition to those obtained by Richardson, who 

 used a, quite different source of ft radiation, leave no doubt 

 as to the identity of secondary rays excited in the different 

 substances by any stimulus, whether by ft or X rays. 



XIX. On the most Effective Primary Capacity for Induction- 

 coils and Testa Coils. By E. Taylor Jones, JJ.Sc, 

 Professor of Physics in the University College of Nortli 

 Wales, Bangor^. 



IN the theory put forward in recent papers J by the writer 

 the induction-coil is regarded as an oscillation trans- 

 former, in which the two circuits are closely coupled, 

 and in which the secondary potential arises from the 

 superposition of two oscillations differing in amplitude, 



* J. Chadwick, Phil. Ma£. vol. xxiv. p. 594 (1912). 

 ] Communicated by the Author. 



J Phil. Mag. xxii. p. 706 (1911^ [with D. E. Roberts]; xxvii. p. 565 

 (1914); xxix. p. 1(1915). 



