DEFLECTION OF POSITIVE RA YS 25

ray particles which were charged before they entered the
electric and magnetic fields have their charges neutralized
before they pass through them, and thus do not experience
the full deflection. On the other hand others which had got
neutralized before they entered the field strike against an
electron or atom and, losing an electron, get ionized by
the collision. In this way they acquire a positive charge in
the field and are deflected by an amount-which depends
upon the stage in their journey at which they picked up the
charge. Thus the quantities we denoted by A and B (see
p. 21) vary from particle to particle, and the values of
ejm cannot be obtained from equation of the type (3) and (4)
where A and B are calculated on the supposition that the
particles are charged for the whole of the time they are
between the poles of the magnet and the plates of the
condenser.

In my first experiments * on this subject the arrangement
was as follows: The cathode K (Fig. 10) had a hole bored

M

FIG. 10.

through it and in this hole a tube F with a very fine bore was

firmly fixed; it is essential to the success of the experiment

that the bore of the tube should be exceedingly fine so as to

1 J. J. Thomson, " Phil. Mag.," VI, xiii, p. 561, the same velocity,