PRESIDENT’S ADDRESS. 15 
contains enormous stores of energy ; this energy is fortunately kept fast 
bound by the corpuscles; if at any time an appreciable fraction were 
to get free, the earth would explode and become a gaseous nebula. 
The matter of which I have been speaking so far is the material 
which builds up the earth, the sun, and the stars, the matter studied 
by the chemist, and which he can represent by a formula; this matter 
occupies, however, but an insignificant fraction of the universe, it forms 
but minute islands in the great ocean of the ether, the substance with 
which the whole universe is filled. 
The ether is not a fantastic creation of the speculative philosopher ; 
it is as essential to us as the air we breathe. For we must remember 
that we on this earth are not living on our own resources; we are 
dependent from minute to minute upon what we are getting from the sun, 
and the gifts of the sun are conveyed to us by the ether. It is to the 
sun that we owe not merely night and day, springtime and harvest, but 
it is the energy of the sun, stored up in coal, in waterfalls, in food, that 
practically does all the work of the world. 
How great is the supply the sun lavishes upon us becomes clear 
‘when we consider that the heat received by the earth under a high 
sun and a clear sky is equivalent, according to the measurements of 
Langley, to about 7,000 horse-power per acre. Though our engineers 
have not yet discovered how to utilise this enormous supply of power, 
they will, I have not the slightest doubt, ultimately succeed in doing so; 
and when coal is exhausted and our water-power inadequate, ib may be 
that this is the source from which we shall derive the energy necessary 
for the world’s work. When that comes about, our centres of industrial 
activity may perhaps be transferred to the burning deserts of the 
Sahara, and the value of land determined by its suitability for the recep- 
tion of traps to catch sunbeams. 
This energy, in the interval between its departure from the sun and 
its arrival at the earth, must be in the space between them. Thus this 
space must contain something which, like ordinary matter, can store up 
energy, which can carry ab an enormous pace the energy associated 
with light and heat, and which can, in addition, exert the enormous 
stresses necessary to keep the earth circling round the sun and the 
moon round the earth. 
The study of this all-pervading substance is perhaps the most fas- 
cinating and important duty of the physicist. 
On the electromagnetic theory of light, now universally accepted, 
the energy streaming to the earth travels through the ether in electric 
waves; thus practically the whole of the energy at our disposal has at 
one time or another been electrical energy. The ether must, then, be 
the seat of electrical and magnetic forces. We know, thanks to the 
_enius of Clerk Maxwell, the founder and inspirer of modern electrical 
theory, the equations which express the relation between these forces, 
