TEE KINETIC THEORY OF MATTER 433 



knocked out of a molecule at once, the residue of the molecule would 

 possess a corresponding number of unit charges, and if this residue were 

 caught by the oil drop, the latter should be seen to jump forward at the 

 instant of capture because of the destruction of the equilibrium between 

 gravity and the electric field ; and, furthermore, from the speed which it 

 assumed, as measured by the time which it took to move over a given 

 number of the divisions in the scale of the eye-piece of the observing 

 telescope, the size of the charge of the captured ions could be determined. 

 The experiment was found to be as interesting and as exciting as trout 

 fishing. The star under observation would often stand perfectly still 

 for five, ten, fifteen or even sixty seconds and then suddenly start 

 forward with a sjjeed which was big or little according to the size of 

 the catch and the size of the drop. When we were using large drops, 

 it was found that two or three adjacent molecules were in occasional 

 instances ionized at once, and therefore two or three separate ions were 

 thrown simultaneously upon the drop, but when the drops were very 

 small, we observed in the course of three months about 500 different 

 catches without finding a single one which corresponded with certainty 

 to the advent of an ion carrying more than one elementary electrical 

 charge, and not more than three or four out of the five hundred which 

 were in any way uncertain. This seems to prove conclusively that the 

 act of ionization by all the types of X-rays and gamma and beta rays of 

 radium which we have been able to try consists in the detaclwient from 

 a neutral molecule of one single electron. 



So far we have considered merely the proof afforded by the present 

 experiments of the atomic theory of electricity. I have not attempted 

 to tell " what electricity is," but have been content with demonstrating, 

 that whatever it is it always appears as an exact multiple of a definite 

 electrical unit. If you ask me to tell you what it is, I should answer by 

 asking you first to tell me what matter is, and if you responded that 

 matter is that out of which this world and the planets and the stars of 

 this universe are made ; that it is something which exists in the form of 

 about 100 different units, or atoms, of relative weights between 1 and 

 240, which atoms unite together in different ways to form molecules; 

 that the average diameter of one of these atoms is two hundred- 

 millionths of a centimeter, then I should answer. Very well, if you are 

 content with that sort of a definition of matter, I will define electricity 

 for you in a similar way and say that electricity is something which is 

 still more fundamental than your atoms of matter since it is a constit- 

 uent of every one of these hundred different types of atoms which you 

 have been describing. It is something too, which like matter is built up 

 out of definite units, but it is unlike matter, in that all of these units are 

 exactly alike so far as we are able to determine, save, however, that a 

 marked difference is found between the positive and negative units. For 



VOL. LXXX. — 29. 



