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’.” 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 Réntgen 
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. 
