Again, J. J. Thomson has brought forward evidence[69] that the positive residues of atoms which shoot through discharge tubes in a direction opposite to that of the cathode rays have suffered multiple ionization. Indeed, he thinks he has evidence that the act of ionization of atoms of mercury consists either in the detachment of one negative electron or else in the detachment of eight. His evidence for the existence [Pg 144] in the case of mercury of multiple charges from one up to eight is certainly very convincing, and it is possible, also, that under his conditions the act of ionization itself may consist in the detachment either of one or of eight electrons as he suggests. Further evidence upon this point must be sought. VI. SUMMARY The results of the studies reviewed in this chapter may be summarized thus: 1. The act of ionization by -rays seems to consist in the shaking off without any appreciable energy of one single electron from an occasional molecule through which the -ray passes. The faster the -ray the less frequently does it ionize. 2. The act of ionization by ether waves, i.e., by X-rays or light, seems to consist in the hurling out with an energy which may be very large, but which depends upon the frequency of the incident ether wave, of one single electron from an occasional molecule over which this wave passes. 3. The act of ionization by rapidly moving -particles consists generally in the shaking loose of one single electron from the atom through which it passes, though in the case of helium, two electrons are certainly sometimes removed at once. It may be, too, that a very slow-moving positive ray, such as J. J. Thomson used, may detach several electrons from a single atom. [Pg 145] CHAPTER VII BROWNIAN MOVEMENTS IN GASES I. HISTORICAL SUMMARY