134 £Jy$ *3F PCSlTirE ELECTRICITY

oxygen atoms which owed their charge to the decomposition of
a mo!ecule of v/ater \vould only be •] f of the maximum energy ;
while if th<2 r,?£at;ve!y electrified oxygen atoms owed their
charge to lh^ decomposition of the molecule of some alcohol of
high molecular v;e!ght their energy would be a much smaller
fraction of the maximum energy. The production of negatively
electrified atoms by the decomposition of molecules would thus
not affect the intensity of the heads of the parabolas corre-
sponding to atoms, they would produce an abrupt increase
in intensity at points on the parabolic arc at a distance from the
depending oa the type of compound from which the
liberated Some observers—for example, Wien,
Hammer—have observed that the negative
more pronounced when water-vapour was ad-
mitted to the tube than when pains were taken to exclude
it, and the suggestion has been made that the negative
constituents are due entirely to this source, I do not think
position is tenable, as I have found the negative oxygen
exceedingly strong after very elaborate precautions had been
to exclude water-vapour, and, moreover, the decom-
position of water-vapour cannot account for the presence
of negatively charged hydrogen atoms, one of the most
prevalent constituents of the stream of particles which form
the rays.

RETROGRADE AND ANODE RAYS

The rays we have hitherto been considering consist of
positively charged particles travelling in the direction in which
particles would be moved by the electric field in the
discharge tube. In addition to these there is another system
of rays travelling in the opposite direction. By far the
larger portion of these rays are cathode rays, i.e. streams ofetic energy due to the full fall of potential