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28 RA ¥S OF POSITIVE ELECTRICITY

the fields, attract a corpuscle whilst in them, get

and for the rest of its journey be free from electric

and magnetic deflections. This view of the origin of these

to me to be proved by the following experiments,.

As on this view these lines are due to particles which are
or discharged in the electric and magnetic fields ; their
intensity, as compared with that of*the parabolas, ought to
diminish If the length of these fields Is reduced. To test this
1 took a photograph with a tube when the lengths of the
electric and magnetic fields were reduced to I mm., the in-
tensity of the fields being Increased In proportion so as to get
deflections comparable with those in the longer fields. With
this very short field the straight lines disappeared, and nothing
except the parabolas and the undeflected central spot was to
be seen on the photographic plate.

Another way of testing this view Is to use magnetic and
electric fields, which are not coterminous. Let us suppose for
example that the magnetic field stretches beyond the electric,
on the camera side. There will be a part of the field where the
particles are exposed to magnetic but not to electric forces.
If a neutralized particle gets Ionized in this region, it will ex-
perience magnetic, I.e. vertical deflection but no electrostatic
or horizontal deflection. Thus with a field of this kind we should
expect the line due to particles which acquired their charge
whilst in the electric field to have the shape shown In Fig. 18.
The straight vertical stem near the origin Is due to the
particles Ionized beyond the electric field, a piece running up
to join the parabola to those ionized Inside this field, the
portion close to the parabola being due to particles which get
Ionized almost as soon as they enter the fields. Photographs
taken with the magnetic field overlapping the electrostatic
show this effect very plainly; one of them is reproduced in
Fig. 19, Plate L, another In Fig. 25, Plate II.



	28 RA ¥S OF POSITIVE ELECTRICITY the fields, attract a corpuscle whilst in them, get and for the rest of its journey be free from electric and magnetic deflections. This view of the origin of these to me to be proved by the following experiments,. As on this view these lines are due to particles which are or discharged in the electric and magnetic fields ; their intensity, as compared with that of*the parabolas, ought to diminish If the length of these fields Is reduced. To test this 1 took a photograph with a tube when the lengths of the electric and magnetic fields were reduced to I mm., the in- tensity of the fields being Increased In proportion so as to get deflections comparable with those in the longer fields. With this very short field the straight lines disappeared, and nothing except the parabolas and the undeflected central spot was to be seen on the photographic plate. Another way of testing this view Is to use magnetic and electric fields, which are not coterminous. Let us suppose for example that the magnetic field stretches beyond the electric, on the camera side. There will be a part of the field where the particles are exposed to magnetic but not to electric forces. If a neutralized particle gets Ionized in this region, it will ex- perience magnetic, I.e. vertical deflection but no electrostatic or horizontal deflection. Thus with a field of this kind we should expect the line due to particles which acquired their charge whilst in the electric field to have the shape shown In Fig. 18. The straight vertical stem near the origin Is due to the particles Ionized beyond the electric field, a piece running up to join the parabola to those ionized Inside this field, the portion close to the parabola being due to particles which get Ionized almost as soon as they enter the fields. Photographs taken with the magnetic field overlapping the electrostatic show this effect very plainly; one of them is reproduced in Fig. 19, Plate L, another In Fig. 25, Plate II.