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26 RA FS OF POSITIVE ELECTRICITY

the carrier C until the tip of the needle NN comes just over

the in question. The carrier C has two movements, one

to the base BB, and the other, by means of the screw

S, at angles to this direction, the position of the point is

off on the two verniers. The plate is placed In the

so that the direction of the magnetic deflection Is

and that of the electrostatic deflection, at right angles,

to BB.

DISCUSSION OF THE PHOTOGRAPHS.

The appearance of a typical photograph produced by the
Impact of the cathode rays on the plate when the pressure on
the camera side of the apparatus Is reduced to about -ooi mm.
of mercury Is shown In Fig. 15, Plate I. In this and the
figures the deflection due to the magnetic field is
vertical, while that due to the electrostatic field is horizontal.
It -will be seen that the curves on the plate are of two
different types.

I. A series of separate parabolic arcs, often of consider-
able length. From the theory given on page 13 it will be
seen that each of these parabolas arises from particles having
the same value of e\m, and that these particles have retained
this charge throughout the whole of the journey through the
electric and magnetic fields. As the velocity of a particle is
by equation (3), p. 12 proportional to the tangent of the angle
which the line joining the origin to the point where the particle
hits the screen makes with the horizontal, It follows that there
is a considerable range of velocities among the particles having
the same value of ejm. In many cases we have velocities
among the same kind of particles differing as much as to make
the velocity of the slowest ones less than one fifth that of the
fastest In some cases the parabolas are of fairly uniform
intensity along the whole of their length. In others as In that



	26 RA FS OF POSITIVE ELECTRICITY the carrier C until the tip of the needle NN comes just over the in question. The carrier C has two movements, one to the base BB, and the other, by means of the screw S, at angles to this direction, the position of the point is off on the two verniers. The plate is placed In the so that the direction of the magnetic deflection Is and that of the electrostatic deflection, at right angles, to BB. DISCUSSION OF THE PHOTOGRAPHS. The appearance of a typical photograph produced by the Impact of the cathode rays on the plate when the pressure on the camera side of the apparatus Is reduced to about -ooi mm. of mercury Is shown In Fig. 15, Plate I. In this and the figures the deflection due to the magnetic field is vertical, while that due to the electrostatic field is horizontal. It -will be seen that the curves on the plate are of two different types. I. A series of separate parabolic arcs, often of consider- able length. From the theory given on page 13 it will be seen that each of these parabolas arises from particles having the same value of e\m, and that these particles have retained this charge throughout the whole of the journey through the electric and magnetic fields. As the velocity of a particle is by equation (3), p. 12 proportional to the tangent of the angle which the line joining the origin to the point where the particle hits the screen makes with the horizontal, It follows that there is a considerable range of velocities among the particles having the same value of ejm. In many cases we have velocities among the same kind of particles differing as much as to make the velocity of the slowest ones less than one fifth that of the fastest In some cases the parabolas are of fairly uniform intensity along the whole of their length. In others as In that