This result is not an hypothesis but a very great probability. This
probability increases when it is noted that the same value for the
constant is met with in the study of very varied phenomena; for
example, in certain theories on radiation. Knowing the mass and energy
of a molecule, it is easy to calculate its speed; and we find that the
average speed is about 400 metres per second for carbonic anhydride,
500 for nitrogen, and 1850 for hydrogen at 0 deg. C. and at ordinary
pressure. I shall have occasion, later on, to speak of much more
considerable speeds than these as animating other particles.
The kinetic theory has permitted the diffusion of gases to be
explained, and the divers circumstances of the phenomenon to be
calculated. It has allowed us to show, as M. Brillouin has done, that
the coefficient of diffusion of two gases does not depend on the
proportion of the gases in the mixture; it gives a very striking image
of the phenomena of viscosity and conductivity; and it leads us to
think that the coefficients of friction and of conductivity are
independent of the density; while all these previsions have been
verified by experiment.
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