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44 RAYS OF POSITIVE ELECTRICITY

will be strongly attracted towards the magnet. If we take the
needles off the needle points and lay them on the disk,
the friction will prevent their rotation relative to the disk. If
we now put the magnet In the same position as It was before
It will be found that the attraction has been very much
diminished.

Thus we should expect the attraction between a neutral
atom and a corpuscle to be very much Increased by the
presence In the atom of corpuscles which can move freely re-
latively to the atom. If these freely moving corpuscles are
which are near the surface and which give rise to the
forces which bind the atoms In the molecule together, we can
readily understand why a neutral molecule should not attract
a corpuscle as vigorously as a neutral atom. For when two
atoms in a molecule are held together by the forces which
they exert on each, the corpuscles in each atom will take up
definite positions in their atoms, and will resist any displace-
ment. Their mobility will thus be diminished and they will
therefore not exert much attraction on a charge of electricity
outside them. We Infer that those atoms which like helium
do not occur among the positive rays with a negative charge
have very few free corpuscles. It is.remarkable that so far as
we know the atoms of the monatomic gases never occur with
a negative charge in these experiments; this Is consistent with
the preceding theory, for the attraction between two atoms de-
pends on the presence of these mobile corpuscles, and If these
are few or sluggish the force may be Insufficient to keep two
atoms together. It would, as we have seen, require a strong
attraction between an atom and a corpuscle to enable the atom
to capture the corpuscle In experiments like these we are con-
sidering, when the atom moves past the corpuscle with a very
great velocity. Franck¹ has shown that even when this

, "Verhand. cL D. Pfays. Ges." 12, 613, 1910.



	44 RAYS OF POSITIVE ELECTRICITY will be strongly attracted towards the magnet. If we take the needles off the needle points and lay them on the disk, the friction will prevent their rotation relative to the disk. If we now put the magnet In the same position as It was before It will be found that the attraction has been very much diminished. Thus we should expect the attraction between a neutral atom and a corpuscle to be very much Increased by the presence In the atom of corpuscles which can move freely re- latively to the atom. If these freely moving corpuscles are which are near the surface and which give rise to the forces which bind the atoms In the molecule together, we can readily understand why a neutral molecule should not attract a corpuscle as vigorously as a neutral atom. For when two atoms in a molecule are held together by the forces which they exert on each, the corpuscles in each atom will take up definite positions in their atoms, and will resist any displace- ment. Their mobility will thus be diminished and they will therefore not exert much attraction on a charge of electricity outside them. We Infer that those atoms which like helium do not occur among the positive rays with a negative charge have very few free corpuscles. It is.remarkable that so far as we know the atoms of the monatomic gases never occur with a negative charge in these experiments; this Is consistent with the preceding theory, for the attraction between two atoms de- pends on the presence of these mobile corpuscles, and If these are few or sluggish the force may be Insufficient to keep two atoms together. It would, as we have seen, require a strong attraction between an atom and a corpuscle to enable the atom to capture the corpuscle In experiments like these we are con- sidering, when the atom moves past the corpuscle with a very great velocity. Franck¹ has shown that even when this , "Verhand. cL D. Pfays. Ges." 12, 613, 1910.