so small that the holes in the medium were all closed up. For this case and for this case alone we know both from Stokes’s and Arnold’s work exactly the law of motion of the droplet.
CHAPTER VI
THE MECHANISM OF IONIZATION OF GASES BY X-RAYS AND RADIUM RAYS
I. EARLY EVIDENCE
Up to the year 1908 the only experiments which threw any light whatever upon the question as to what the act of ionization of a gas consists in were those performed by Townsend[56] in 1900. He had concluded from the theory given on [p. 34] and from his measurements on the diffusion coefficients and the mobilities of gaseous ions that both positive and negative ions in gases carry unit charges. This conclusion was drawn from the fact that the value of
in the equation
came out about
