578 Professor J. J. Thomson [April 19, 



In fact, in every case in which the transport of negative electricity 

 through gas at a low pressure (i.e., when the corpuscles have nothing 

 to stick to) has been examined, it has been found that the carriers of 

 the negative electricity are these corpuscles of invariable mass. 



A very different state of things holds for the positive electricity. 

 The masses of the carriers of positive electricity have been deter- 

 mined for the positive electrification in vacuum tubes by Wien and 

 by Ewers, while I have measured the same thing for the positive 

 electrification produced in a gas by an incandescent wire. The 

 results of these experiments show a remarkable difference between 

 the property of positive and negative electrification, for the positive 

 electricity, instead of being associated with a constant mass T * of 

 that of the hydrogen atom, is found to be always connected with a 

 mass which is of the same order as that of an ordinary molecule, 

 and which, moreover, varies with the nature of the gas in~which the 

 electrification is found. 



These two results, the invariability and smallness of the mass of 

 the carriers of negative electricity, and the variability and compara- 

 tively large mass of the carriers of positive electricity, seem to me to 

 point unmistakably to a very definite conception as to the nature of 

 electricity. Do they not obviously suggest that negative electricity 

 consists of these corpuscles, or, to put it the other way, that these 

 corpuscles are negative electricity, and that positive electrification 

 consists in the absence of these corpuscles from ordinary atoms ? 

 Thus this point of view approximates very closely to the old one-fluid 

 theory of Franklin ; on that theory electricity was regarded as a fluid, 

 and changes in the state of electrification were regarded as due to the 

 transport of this fluid from one place to another. If we regard 

 Franklin's electric fluid as a collection of negatively electrified cor- 

 puscles, the old one-fluid theory will, in many respects, express the 

 results of the new. We have seen that we know a good deal about 

 the " electric fluid " ; we know that it is molecular,or rather corpuscular 

 in character ; we know the mass of each of these corpuscles and the 

 charge of electricity carried by it ; we have seen, too, that the velocity 

 with which the corpuscles move can be determined without difficulty. 

 In fact, the electric fluid is much more amenable to experiment than 

 an ordinary gas, and the details of its structure are more easily 

 determined. 



Negative electricity (i.e., the electric fluid) has mass ; a body 

 negatively electrified has a greater mass than the same body in the 

 neutral state ; positive electrification, on the other hand, since it in- 

 volves the absence of corpuscles, is accompanied by a diminution in 

 mass. 



An interesting question arises as to the nature of the mass of 

 these corpuscles, which we may illustrate in the following way. When 

 a charged corpuscle is moving, it produces in the region around it 

 a magnetic field whose strength is proportional to the velocity of the 

 corpuscle ; now in a magnetic field there is an amount of energy pro- 



