312 Prof. J. J. Thomson on Cathode Ray s. 



molecules in the crowd, but to the number of the individual 

 corpuscles. The mean free path is inversely proportional to 

 the number of collisions in unit time, and so is inversely pro- 

 portional to the number of corpuscles in unit volume; now as 

 these corpuscles are all of the same mass, the number of 

 corpuscles in unit volume will be proportional to the mass of 

 unit volume, that is the mean free path will be inversely 

 proportional to the density of the gas. We see, too, that so, 

 long as the distance between neighbouring corpuscles is large 

 compared with the linear dimensions of a corpuscle the mean 

 free path will be independent of the way they are arranged, 

 provided the number in unit volume remains constant, that is 

 the mean free path will depend only on the density of the 

 medium traversed by the corpuscles, and will be independent 

 of its chemical nature and physical state : this from Lenard's 

 very remarkable measurements of the absorption of the cathode 

 rays by various media, must be a property possessed by the 

 carriers of the charges in the cathode rays. 



Thus on this view we have in the cathode rays matter in a 

 new state, a state in which the subdivision of matter is carried 

 very much further than in the ordinary gaseous state : a state 

 in which all matter — that is, matter derived from different 

 sources such as hydrogen, oxygen, &c. — is of one and the 

 same kind ; this matter being the substance from which all 

 the chemical elements are built up. 



With appliances of ordinary magnitude, the quantity of 

 matter produced by means of the dissociation at the cathode 

 is so small as to almost to preclude the possibility of any direct 

 chemical investigation of its properties. Thus the coil I used 

 would, I calculate, if kept going uninterruptedly night and 

 day for a year, produce only about one three-millionth part 

 of a gramme of this substance. 



The smallness of the value of m/e is, I think, due to the 

 largeness of e as well as the smallness of m. There seems to 

 me to be some evidence that the charges carried by the cor- 

 puscles in the atom are large compared with those carried by 

 the ions of an electrolyte. In the molecule of HC1, for 

 example, I picture the components of the hydrogen atoms as 

 held together by a great number of tubes of electrostatic 

 force; the components of the chlorine atom are similarly held 

 together, while only one stray tube binds the hydrogen atom 

 to the chlorine atom. The reason for attributing this high 

 charge to the constituents of the atom is derived from the 

 values of the specific inductive capacity of gases : we may 

 imagine that the specific inductive capacity of a gas is due to 

 the setting in the electric field of the electric doublet formed 



