May 29, 1913] 



NATURE 



i35 



graph of the heavier gases in the atmosphere. You 

 will notiee that the parabolas corresponding to many 

 of the elements start from points which are all in the 

 same vertical line ; this indicates that the atoms or 

 molecules which form these parabolas all carry the 

 same charge. Several of these lines, however, do not 

 follow this rule; you will notice, for example, that 

 the neon line has a prolongation which comes nearer 

 than the normal line to the vertical line drawn through 

 the undeflected spot. Measurement of the photograph 

 shows that the neon line begins at a distance from 

 this vertical line which is only half the normal dis- 

 tance; this shows that some of the neon atoms in 

 the positive rings possess two charges of electricity; 

 the majority of them, however, only possess one. If 

 you examine the argon line you will find that it comes 

 even nearer to the vertical than the neon line ; in 

 fact, it begins at a distance from the vertical only 

 one-third of the normal distance; this proves that the 

 argon atom can have as many as three charges of 

 electricity. If now you examine the krypton line 

 you will find that it comes nearer to the vertical line 

 than even the argon ; its least distance is one-fourth 

 of the normal distance, showing that the krypton 

 atom mav have as many as four charges. The mer- 

 cury line comes so close to the vertical line that it is 

 only on large photographs that it can be seen that 

 there is in reality an interval ; this interval is only 

 one-i ighth of the normal interval, showing that mer- 

 cury may acquire eight positive charges, i.e. that it 

 may lose eight corpuscles. The mercury atom when 

 it is on this line must have only the normal charge, 

 i.e. it must have regained all but one of the corpuscles 

 it previously lost ; if it had retained two positive 

 charges it would have been on the line corresponding 

 to the atomic weight 200/2 or 100; if it had retained 

 3, or 4, 5, 6, 7, S on the lines corresponding to the 

 atomic weights, 200/3, 200 /4> 200 /Si 2 oo/6, 200/7, 

 200 /S respectively. All these except the last have 

 been detected on the plate. The lines corresponding 

 to the multiple charges on krypton, argon, and neon 

 have also been detected. It appears, then, that in 

 a vacuum tube a mercury atom, for example, may 

 be ionised in two ways ; in the one way the atom 

 loses one corpuscle, in the other it loses eight. 



I would suggest that these two types of ionisation 

 mav 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 exceedingly 

 small bodv moving with a very great velocity, it can 

 I it" freely through the atom, and the collision it 

 makes with the atom is really a collision with a cor- 

 puscle inside the atom ; this may result in the corpuscle 

 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. 

 1 <md 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 propor- 

 tioned to the square root of the atomic weight, hence 



NO. 22/4, VOL. 91] 



the heavy elements have a larger number of detach- 

 able 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 appeared 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 11... 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 exceed- 

 ingly faint, and when there is not a trace of a carbon 

 atom with even two charges, though the doubly- 

 charged carbon atom occurs readily under certain con- 

 ditions. 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 substance 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, 1 

 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 appear- 

 ance was always fortuitous and sometimes for weeks 

 together the plates would not show a trace of the 

 line. The line sometimes 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 

 tedious, to find the conditions under which the line 

 appeared. I tried filling the discharge-vessel with all 

 the gases and vapours described in the books on 

 chemistry without success. At last I tried bombard- 

 ing various substances with kathode rays. Under this 

 treatment the substances give off considerable quali- 

 ties of gas the greater part of which is hydrogen, 

 carbonic acid, or carbon monoxide. When I came to 

 analyse by the positive rays the gases given off in this 

 way, I found that with a large number of substances 

 these gases contained the substances giving the_ three 

 lines, so that I was now in a position to get this line 

 whenever I wanted it, and investigate the properties 

 of the gas to which it owes its origin. The question 

 of the "gases absorbed and given off by solids is an 

 extremely interesting one, and a considerable number 

 of investigations have been made on it. In all these, 

 so far as I know, the method has been to heat the 

 solid to a high temperature, and then measure and 

 analyse the very considerable amount of gas which 

 is driven off bv the heating. So far as I know, no 

 experiments have been made in which the gases were 

 driven off bv bombardment with kathode rays. This 

 treatment, however, will cause the emission of gas 

 even when ordinary heating fails to do so. 



Belloc, who has' recently published 2 some interest- 

 ing experiments on this subject, after spending about 

 six months in a fruitless attempt to get a piece of iron 

 in a state in which it would no longer give off gas 

 when heated, came to the conclusion that, for practical 

 purposes, a piece of iron must be regarded as an 

 inexhaustible reservoir of gas. There are some in- 

 teresting features about the emission of gas from a 

 heated solid. If the body is kept for a long time in a 

 vacuum at a high temperature, the emission of gas 

 becomes too small to be detected; if after this treat- 

 ment the temperature is raised considerably, there will 

 be a further copious emission of gas, which again 

 diminishes as the heating continues. After it has 

 fallen to zero, all that is necessary is to raise the tem- 

 perature again and vou will get a fresh supply of 

 gas; and so far as "my experience goes, after you 



-' Ann. ,/,■ Chimit <•• dt Physique [8), xviii., p. 569. 



