52 RAYS OF POSITIVE ELECTRICITY

some 100 volts, and as the original energy in these rays is
generally above 20,000 volts the diminution would have been
too small to be detected, The case, however, is very different
when we have 100,000 collisions as in the a rays ; here the
loss of energy is comparable with that possessed initially by
these rays.

Wien (/. £.) has determined the values of the quantities
we have denoted by 1^ A2 for hydrogen, oxygen, nitrogen,
Doth in the cases when the positive rays were made from
:he gas through which they passed and also when they were
nade from different gases. In the case of hydrogen rays
passing through hydrogen he finds that ^ (reduced to
atmospheric pressure on the supposition that it varies
inversely as the pressure) is

6 . 15 x io~5 cm.
and that V=34 • 8 X io"5 cm.

The beam of positive rays included both atoms and mole-
cules of hydrogen, so that these values are intermediate
between the values of I for atoms and molecules.

The mean free path of a molecule of hydrogen through
hydrogen is according to the kinetic theory of gases io~5cm.,
and that of an atom of hydrogen through molecules of
hydrogen about 2 X iO~~5cm, The values of 1, though greater
than the ordinary free paths, are of the same order of magnitude,
so that a positive ray particle could not make many collisions
of the type of those contemplated in the kinetic theory oi
gases without altering its electrical state. An interesting
point brought out by Wien's experiments is that the values
of 1 do not seem to depend upon the electro-positive or
electro-negative character of the gas. He found that the
values of I when hydrogen positive rays passed through
oxygen, which is strongly electro-negative, were much the same
as the values when these rays passed through nitrogen, whichgas, i. e. a quantity of the order of 10 volts; hence, if