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CONTINUOUS VARIATION 15

they are very much more massive than the particles In the
cathode rays for which ejm = 1*7 x i o⁷. The displaced
particles In this experiment were spread out into a continuous
straight band, Indicating, according to the theory of the effect
of electric and magnetic fields on charged particles, that in the
positive rays there are particles giving all values of e\m from
zero up to about 10,000. This would Imply, assuming that
the charge on 'each particle Is the same, that the masses of the
particles vary continuously from a certain value comparable
with the mass of an atom of hydrogen up to a value which Is
very large in comparison with this mass. This continuous
variation In the value of efm is contrary to what might be ex-
pected, for, from the molecular theory of gases, the masses
available In the gas would not vary continuously but would
increase by finite steps, the smallest step being the mass of the
atom of hydrogen : again the results of many different lines of
investigation lead to the conclusion that e like m does not vary
continuously, but that all electrical charges are multiples of a
unit charge whose value in electrostatic measure Is 4*8 x 10 ~ ¹⁰.
Again it would appear from the uniformity of the luminosity
produced by the displaced positive rays that there is no special
kind of atom which Is predominant among these rays. For If
there had been a great excess of particles of one kind, these
would have produced a very bright spot on the glass If they
had all been moving with the same velocity, or a bright arc of
a parabola if they had been moving with varying velocities.
The experiments which I will now describe, which I made in
1906, show that the discrepancies between the theory and the
experiments are due to the pressure of the gas In the discharge
tube in Wien's experiments having been so high that the
particles forming the positive rays collided with the molecules
of the gas whilst they were passing through the electric and
magnetic fields. The effect of these collisions is to ionize the



	*CONTINUOUS* VARIATION 15 they are very much more massive than the particles In the cathode rays for which ejm = 17 x i o⁷. The displaced particles In this experiment were spread out into a continuous straight band, Indicating, according to the theory of the effect of electric and magnetic fields on charged particles, that in the positive rays there are particles giving all values of e\m* from zero up to about 10,000. This would Imply, assuming that the charge on 'each particle Is the same, that the masses of the particles vary continuously from a certain value comparable with the mass of an atom of hydrogen up to a value which Is very large in comparison with this mass. This continuous variation In the value of efm is contrary to what might be ex- pected, for, from the molecular theory of gases, the masses available In the gas would not vary continuously but would increase by finite steps, the smallest step being the mass of the atom of hydrogen : again the results of many different lines of investigation lead to the conclusion that e like m does not vary continuously, but that all electrical charges are multiples of a unit charge whose value in electrostatic measure Is 4*8 x 10 ~ ¹⁰. Again it would appear from the uniformity of the luminosity produced by the displaced positive rays that there is no special kind of atom which Is predominant among these rays. For If there had been a great excess of particles of one kind, these would have produced a very bright spot on the glass If they had all been moving with the same velocity, or a bright arc of a parabola if they had been moving with varying velocities. The experiments which I will now describe, which I made in 1906, show that the discrepancies between the theory and the experiments are due to the pressure of the gas In the discharge tube in Wien's experiments having been so high that the particles forming the positive rays collided with the molecules of the gas whilst they were passing through the electric and magnetic fields. The effect of these collisions is to ionize the