to anode rays; the difference is exceptionally well
marked in helium, where the cathode ray luminosity is blue while that
due to the positive rays is red. The luminosity produced when the rays
strike against solids is also quite distinct. The cathode rays make the
body emit a continuous spectrum, while the spectrum produced by the
positive rays often shows bright lines. Thus lithium chloride under
cathode rays gives out a steely blue light and the spectrum is
continuous, while under the positive rays the salt gives out a brilliant
red light and the spectrum shows the red helium line. It is remarkable
that the lines on the spectra of the alkali metals are much more easily
produced when the positive rays fall on the oxide of the metal than when
they fall on the metal itself. Thus when the positive rays fall on a
pool of the liquid alloy of sodium and potassium the specks of oxide on
the surface shine with a bright yellow light while the untarnished part
of the surface is quite dark.

W. Wien (_Wied. Ann._ 65, p. 445) measured the values of e/m for the
particles forming the positive rays. Other measurements have been made
by Ewers (_Wied. Ann._ 69, p. 167) and J. J. Thomson (_Phil. Mag._ 13,
p. 561). The differences between the values of e/m for the cathode and
positive rays are very remarkable. For cathode rays whose velocity does
not approach that of light, e/m is always equal to 1.7 X 10^8, while for
the positive rays the greatest value of this quantity yet observed is
10^4, which is also the value of e/m for the hydrogen ions in the
electrolysis of dilute solutions. In some experiments made by J. J.
Thomson (_Phil. Mag._, 14, p. 359) it was found that when the pressure
of the gas was not too low the bright spot produced by the impact of a
pencil of these rays on a phosphorescent screen is deflected by electric
and magnetic forces into a continuous band extending on both sides of
the undeflected position. The portion on one side is in general much
fainter than that on the other. The direction of this deflection shows
that it is produced by particles charged with negative electricity,
while the brighter band is due to particles charged with positive
electricity. The negatively electrified particles which produce the band
c.c are not corpuscles, for from the electric and magnetic deflections
we can find the value of e/m. As this proves to be equal to 10^4, we see
that the mass of the carrier of the negative charge is compa