﻿61 Dr. W. F. Gr. Swann on the Effects of Uniform Motion 



is given as about that corresponding to a potential difference 

 of 3 volts. Examination of the form of the curve when the 

 potential difference is so large that the current is nearly 

 saturated probably does not give any information as to the 

 maximum speed of the rays. 



It is shown that there is considerable evidence that the 

 speed of the rays is independent of the speed of the alpha 

 rays by which they are excited. Such evidence as there 

 is — but there is not very much — shows that the speed is 

 also independent of the material from which the rays are 

 emitted. It can be confidently asserted that there is no such 

 difference between the secondary delta radiation from 

 aluminium and gold as there is, for example, between the 

 secondary Rontgen radiations from those metals. 



It is also difficult to compare with any certainty the 

 quantity of the emergent and incident radiation. A con- 

 sideration of the experiments described in this paper shows 

 that the conclusion advanced in the previous paper that the 

 incident radiation is greater than the emergent is quite 

 unjustified ; there is no evidence that the amount of the 

 two radiations is not equal. 



The conclusion that polonium emits a irue delta radiation, 

 which is not merely a secondary radiation excited by the 

 aipha rays, is also withdrawn. 



In the final paragraphs of the paper considerations are put 

 forward to show that the magnetic method of measuring 

 the speed of the rays, at any rate in the form in which it 

 has been used by previous observers, is as untrustworthy as 

 the method which has been attempted in these papers. 



The University, Leeds. 

 July, 1911. 



Y. A Deduction of the Effects of Uniform Translator y 

 Motion, from the Electrical Theory of Matter, without the 

 Employment of a Transformation of the Electromagnetic 

 Equations. By W. F. GL Swann, D.Sc, A.R.C.S., 

 Assistant Lecturer in Physics at the University of Sheffield *. 



IT is generally recognized that when a piece of matter is 

 set in motion with velocity r, it contracts in the ratio 



( 1 — tt 2 ) wnere Q i s the velocity of light. This fact has 



been explained by Sir Joseph Larmor, and by Lorentz, as 

 following; from the electrical constitution of matter, and other 



* Communicated by the Author, 



