710 Proceedings of Royal Society of Edinburgh. [sess. 
high enough, I do not see why even insulators should not become 
good conductors. For the heat vibrations, even without the 
pockets and corners, which resist the free circulation of the 
ether, must trap a good deal of the new motion of electricity. 
That is, the particle-speed produced by the condensations must 
be increased by the electrical motion, and consequently the heat 
vibrations increased, and a good deal of the electrical motion 
transformed into heat. But at the zero temperature, when all 
vibration has ceased, and the pressure of the ether throughout 
the body has become constant, and especially where there is 
free circulation of the ether, so that any small tremors which 
might possibly be generated by the electrical motion would have 
very little effect, it is easy to see that ordinary conducting bodies 
would become perfect conductors. For then none of the motion 
could be trapped and absorbed in the vibrations, because none 
of the latter existed. 
35. While trying to puzzle out the enigma of conduction I 
came to the conclusion, whether rightly or wrongly, that com- 
munity of atomic volume involved also community of mean 
particle-speed. It does not necessarily follow that because their 
apparent volumes are the same their real or mean volumes are 
so, for the latter are proportional to the cubes of their mean 
radii, and the former is a combination of this with their amplitude 
of vibration. Every atom while executing a complete vibration 
passes from a state of expansion to a state of compression, and back 
again ; and its radius will pass through all stages from a maximum 
to a minimum, and back again. We can only measure the volume 
of any body at the maximum phase of its vibrations, not at the 
minimum ; therefore when testing the specific gravity it is the 
maximum volume which counts. In two bodies of the same 
atomic volume that body whose atoms possess the greater 
number of particles will have the greater mean atomic volume, 
but it seems to me, and my reasoning is supported by analogies 
from the kinetic theory of gases, the body with the less massive 
atoms occupies the same extreme or maximum space by reason 
of its atoms’ greater amplitude of vibration. I mean, of course, 
these remarks to apply to bodies in the solid state. In the 
gaseous state we know, of course, that the mean space occupied 
