THE METHOD OF POSITIVE RAYS 525 



I would suggest that these two types of ionization may result from the 

 two different types of collision which the atom must experience. The 

 first type is collision with a corpuscle ; since the corpuscle is an exceed- 

 ingly small hody moving with a very great velocit}*, it can pass freely 

 through the atom, and the collision it makes with the atom is really a 

 collision with a corpuscle inside the atom; this may result in the cor- 

 puscle it strikes acquiring such a great velocity that it is able to escape 

 from the atom ; this type of collision will result in the detachment of a 

 single corpuscle. The second type of collision is when the atom collides 

 with another atom and not with another corpuscle; the result of this 

 collision may be that the atom suffers a sudden change in its velocity. 

 This change is not at first shared by the corpuscles, so that these just 

 after the collision may have a very considerable velocity relative to the 

 atom. If there are several corpuscles which are comparatively loosely 

 attached to the atom, these may all be detached from it and leave it 

 with a positive charge corresponding to the number shaken out. It is 

 this type of collision which we regard as giving the multiply-charged 

 ions, and we see that the magnitude of the charge is a measure of the 

 number of corpuscles in an atom which are readily 'detachable from it. 

 We have seen that the greater the atomic weight the greater the charge 

 it can acquire, the maximum charge being roughly proportioned to the 

 square root of the atomic weight, hence the heavy elements have a 

 larger number of detachable corpuscles than the lighter ones. 



Another application of the method I should like to bring before you 

 is the use of it for the discovery and investigation of a new substance. 

 I have in previous lectures said that sometimes there apj)eared on the 

 plates a line corresponding to a particle with an atomic weight 3 ; this 

 must either be a new element or a polymeric modification of hydrogen, 

 represented by H 3 . The other possibility that it is a carbon atom with 

 four charges is put out of court by the fact that it frequently occurs 

 when the carbon line is exceedingly faint, and when there is not a trace 

 of a carbon atom with even two charges, though the doubly-charged car- 

 bon atom occurs readily under certain conditions. In addition to this, 

 the carbon atom parabola never approaches the vertical near enough 

 to allow of its having four charges. I thought the study of the sub- 

 stance producing this line would be of interest, and I have for some time 

 been working at it. and although the research is by no means completed, 

 I have obtained some results which I should like to bring before you. 



At first I was greatly hindered by not knowing the conditions under 

 which the line occurred ; although it appeared from time to time on the 

 plates, its appearance was always fortuitous and sometimes for weeks 

 together the plates would not show a trace of the line. The line some- 

 times appeared, but why it did so was a mystery, and I could not get 

 it when I wanted it. I began an investigation, which proved long and 



