1904 - 5 .] Mr J. Fraser on Electricity based on Bubble Atom. 711 
by all molecules at the same temperature and pressure is pro- 
portional to the square of their speed, and so here, if we look 
upon the particles as molecules, the mean space which they occupy 
is proportional also to the square of their speed. Again, in the 
kinetic theory the lighter atoms make up for their lightness by 
their speed, so in the solid state, if they are also small, they make 
up for their smallness by their greater amplitude of vibration. 
Remember in weighing this point that their maximum volumes 
are equal , but that their minimum volumes may be greatly 
different, being always less for the lighter elements, so that their 
mean volumes may be greatly different. 
36. We are now in a position to test whether and in what 
degree the radiation of heat affects the electrical conduction of 
bodies. For the radiation of heat by solid bodies depends upon 
the amplitude and period of vibration, and the strength of the bonds 
uniting the molecules ; and, since bodies of the same atomic 
volume must, according to my theory, have the same elasticity 
or resistance to compression, they must also have the same period 
of vibration.* We have then in our hands, in order to calculate 
their radiation of heat, the atomic weight, the amplitude of 
vibration (the periods not being necessary since we are choosing 
conditions under which these are the same), and the strength of 
their bonds, which is measured by their melting points. The 
rule, then, according to these assumptions, for calculating their 
radiation of heat and consequent resistance to electrical con- 
duction is as follows : — 
Rule to Find the Electrical Resistance of Metals. 
1st. It is inversely as the square of the cube roots of the atomic 
weights ; 
2nd. Directly as the melting points in the scale of absolute 
temperature ; and 
3rd. Directly as the atomic volume. 
I found when I tried this rule that it answered admirably in 
the case of silver, copper and aluminium ; their resistances 
* Pendulums of the same length have the same period of vibration irre- 
spective of amplitude or weight of bob. 
