Radio-activity 569 



are led therefore to regard the corpuscle from one aspect as a dis- 

 embodied charge of electricity, and to identify it with the electron 

 of Lorentz and Larmor. 



Thus, on this theory, matter and electricity are identified; and 

 a great simplification of our conception of the physical structure 

 of Nature is reached. Moreover, from our present point of 

 view, a common basis for matter suggests or implies a common 

 origin, and a process of development possibly intelligible to our 

 minds. The idea of the evolution of matter becomes much more 

 probable. 



The question of the nature and physical meaning of a corpuscle or 

 electron remains for consideration. On the hypothesis of a universal 

 luminiferous aether, Larmor has suggested a centre of aethereal 

 strain "a place where the continuity of the medium has been broken 

 and cemented together again (to use a crude but effective image) 

 without accurately fitting the parts, so that there is a residual strain 

 all round the place 1 ." Thus he explains in quasi-mechanical terms 

 the properties of an electron. But whether we remain content for 

 the time with our identification of matter and electricity, or attempt 

 to express both of them in terms of hypothetical aether, we have made 

 a great step in advance on the view that matter is made up of 

 chemical atoms fundamentally distinct and eternally isolated. 



Such was the position when the phenomena of radio-activity 

 threw a new light on the problem, and, for the first time in the history 

 of science, gave definite experimental evidence of the transmutation 

 of matter from one chemical element to another. 



In 1896 H. Becquerel discovered that compounds of the metal 

 uranium continually emitted rays capable of penetrating opaque 

 screens and affecting photographic plates. Like cathode and Rontgen 

 rays, the rays from uranium make the air through which they pass 

 a conductor of electricity, and this property gives the most convenient 

 method of detecting the rays and of measuring their intensity. An 

 electroscope may be made of a strip of gold-leaf attached to an 

 insulated brass plate and confined in a brass vessel with glass 

 windows. When the gold-leaf is electrified, it is repelled from the 

 similarly electrified brass plate, and the angle at which it stands 

 out measures the electrification. Such a system, if well insulated, 

 holds its charge for hours, the leakage of electricity through the air 

 being very slow. But, if radio-active radiation reach the air within, 

 the gold-leaf falls, and the rate of its fall, as watched through a 



1 Larmor, loc. cit. 



