ges of negative
electricity in rapid motion. By measuring the deflection produced by
magnetic and electric fields we can determine the velocity with which
these particles moved and the ratio of the mass of the particle to the
charge carried by it.

We may conclude from the experiments that the value of m/e for the
particles constituting the cathode rays is of the order 1/1.7 X 10^7,
and we have seen that m/e has the same value in all the other cases of
negative ions in a gas at low pressure for which it has been
measured--viz. for the ions produced when ultra-violet light falls on a
metal plate, or when an incandescent carbon filament is surrounded by a
gas at a low pressure, and for the [beta] particles given out by
radio-active bodies. We have also seen that the value of the charge on
the gaseous ion, in all cases in which it has been measured--viz. the
ions produced by Rontgen and uranium radiation, by ultra-violet light,
and by the discharge of electrification from a point--is the same in
magnitude as the charge carried by the hydrogen atom in the electrolysis
of solutions. The mass of the hydrogen alone is, however, 10^-4 times
this charge, while the mass of the carriers of negative electrification
is only 1/1.7 X 10^7 times the charge; hence the mass of the carriers of
the negative electrification is only 1/1700 of the mass of the hydrogen
atom. We are thus, by the study of the electric discharge, forced to
recognize the existence of masses very much smaller than the smallest
mass hitherto recognized.

Direct determinations of the velocity of the cathode rays have been
made by J. J. Thomson (_Phil. Mag._ 38, p. 358), who measured the
interval between the appearance of phosphorescence on two pieces of
glass placed at a known distance apart, and by Maiorana (_Nuovo
Cimento_, 4, 6, p. 336) and Battelli and Stefanini (_Phys. Zeit._ 1,
p. 51), who measured the interval between the arrival of the negative
charge carried by the rays at two places separated by a known
distance. The values of the velocity got in this way are much smaller
than the values got by the indirect methods previously described: thus
J. J. Thomson at a fairly high pressure found the velocity to be 2 X
10^7 cm./sec. Maiorana found values ranging between 10^7 and 6 X 10^7
cm./sec, and Battelli and Stefanini values ranging from 6 X 10^6 to
1.2 X 10^7. In these methods it is very difficult to eliminate the
effect of the int