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NATURE OF POSITIVE I?AYS 7

RECTILINEAR PROPAGATION OF THE POSITIVE

RAYS.

This can be shown by placing a solid obstacle in the path
of a pencil of positive rays: this casts a shadow on the part of
the tube which was phosphorescing under the impact of these
rays. Comparing the shape of the shadow with that of the ob~
stacle, it is found that the shadow is very approximately the
projection of the outside of the solid on., the walls of the tube
by lines passing through the hole in the cathode through which
the pencil of positive rays emerges.

ON THE NATURE OF THE POSITIVE RAYS, THEIR DEFLEC-
TION BY ELECTRIC AND MAGNETIC FORCES.

As cathode rays were proved to be negatively electrified
particles by the study of the deflections they experience when
acted on by magnetic and electric forces, and as these deflec-
tions gave the means of finding the mass arid velocity of the
cathode particles, it was natural to attempt to apply the same
methods to the positive rays. It was not, however, until
twelve years had elapsed since the discovery of the rays that
any effect of a magnetic field on them was detected. A small
permanent magnet held near a bundle of cathode rays produces
a very appreciable effect; it has, however, no apparent action
on the positive rays : as a matter of fact the deflection due to
a magnetic field on the positive rays is at most about 2 per
cent of the deflection of the cathode rays, the deflections be-
ing measured at equal distances from the cathode. In 1898,
however, Wien, by the use of very powerful magnetic fields,
proved that the positive rays were deflected by magnetic
forces.¹

Before discussing Wien's experiments it will be convenient

*W. Wien, « Verb. d. phys. Gesell.," 17,1898.



	NATURE OF POSITIVE I?AYS 7 RECTILINEAR PROPAGATION OF THE POSITIVE RAYS. This can be shown by placing a solid obstacle in the path of a pencil of positive rays: this casts a shadow on the part of the tube which was phosphorescing under the impact of these rays. Comparing the shape of the shadow with that of the ob~ stacle, it is found that the shadow is very approximately the projection of the outside of the solid on., the walls of the tube by lines passing through the hole in the cathode through which the pencil of positive rays emerges. ON THE NATURE OF THE POSITIVE RAYS, THEIR DEFLEC- TION BY ELECTRIC AND MAGNETIC FORCES. As cathode rays were proved to be negatively electrified particles by the study of the deflections they experience when acted on by magnetic and electric forces, and as these deflec- tions gave the means of finding the mass arid velocity of the cathode particles, it was natural to attempt to apply the same methods to the positive rays. It was not, however, until twelve years had elapsed since the discovery of the rays that any effect of a magnetic field on them was detected. A small permanent magnet held near a bundle of cathode rays produces a very appreciable effect; it has, however, no apparent action on the positive rays : as a matter of fact the deflection due to a magnetic field on the positive rays is at most about 2 per cent of the deflection of the cathode rays, the deflections be- ing measured at equal distances from the cathode. In 1898, however, Wien, by the use of very powerful magnetic fields, proved that the positive rays were deflected by magnetic forces.¹ Before discussing Wien's experiments it will be convenient *W. Wien, « Verb. d. phys. Gesell.," 17,1898.