14 PRESIDENT’S ADDRESS. 
particles are much more readily deflected, and these have been interpreted 
as proving the existence of positive units comparable in mass with the 
negative ones. I have found, however, that in these cases the positive 
particles are moving very slowly, and that the ease with which they 
are deflected is due to the smallness of the velocity and not to that of 
the mass. It should, however, be noted that M. Jean Becquerel has 
observed in the absorption spectra of some minerals, and Professor 
Wood in the rotation of the plane of polarisation by sodium vapour, 
effects which could be explained by the presence in the substances 
of positive units comparable in mass with corpuscles. This, how- 
ever, is not the only explanation which can be given of these effects, 
and at present the smallest positive electrified particles of which we 
have direct experimental evidence have masses comparable with that 
of an atom of hydrogen. 
A knowledge of the mass and size of the two units of electricity, 
the positive and the negative, would give us the material for constructing 
what may be called a molecular theory of electricity, and would be a 
starting-point for a theory of the structure of matter; for the most 
natural view to take, as a provisional hypothesis, is that matter is just a 
collection of positive and negative units of electricity, and that the 
forces which hold atoms and molecules together, the properties which 
differentiate one kind of matter from another, all have their origin in 
the electrical forces exerted by positive and negative units of electricity, 
grouped together in different ways in the atoms of the different elements. 
As it would seem that the units of positive and negative electricity 
are of very different sizes, we must regard matter as a mixture containing 
systems of very, different types, one type corresponding to the small cor- 
puscle, the other to the large positive unit. 
Since the energy associated with a given charge is greater the smaller 
the body on which the charge is concentrated, the energy stored up 
in the negative corpuscles will be far greater than that stored up by 
the positive. The amount of energy which is stored up in ordinary 
matter in the form of the electrostatic potential energy of its corpuscles 
is, I think, not generally realised. All substances give out corpuscles, 
so that we may assume that each atom of a substance contains at least 
one corpuscle. From the size and the charge on the corpuscle, both of 
which are known, we find that each corpuscle has 8 x 10-7 ergs of 
energy; this is on the supposition that the usual expressions for the 
energy of a charged body hold when, as in the case of a corpuscle, 
the charge is reduced to one unit. Now in one gramme of hydrogen 
there are about 6 X 10?% atoms, so if there is only one corpuscle in each 
atom the energy due to the corpuscles in a gramme of hydrogen would 
be 48 x 10'* ergs, or 11 X 10° calories. This is more than seven times 
the heat developed by one gramme of radium, or than that developed by 
the burning of five tons of coal. Thus we see that even ordinary matter 
