ON BODIES SMALLER THAN ATOMS. 331 



thus be diffused tliroiiijli the metal swarms of these corpuscles, these 

 will be moving about in all directions like the molecules of a gas and, 

 as they can gain or lose energy by colliding with the molecule of the 

 metal, we should expect by the kinetic theory of gases that they will 

 acquire such an average velocity that the mean kinetic energy of a 

 corpuscle moving about in the metal is equal to that possessed by a 

 molecule of a gas at the temperature of the metal; this would make 

 the average velocity of the corpuscles at 0° C. about 10^ centimeters per 

 second. This swarm of negatively electrified corpuscles when exposed 

 to an electric force will be sent drifting along in the direction opposite 

 to the force; this drifting of the corpuscles will be an electric current, 

 so that we could in this way explain the electrical conductivity of 

 metals. 



The amount of electricity carried across unit area under a given 

 electric force will depend upon and increase with (1) the number 

 of free corpuscles per unit volume of the metal, (2) the freedom with 

 which these can move under the force between the atoms of the 

 metal; the latter will depend upon the average velocity of these cor- 

 puscles, for if they are moving with very great rapidity the electric 

 force will have very little time to act before the corpuscle collides 

 with an atom, and the effect produced by the electric force annulled. 

 Thus the average velocity of drift imparted to the corpuscles by the 

 electric field will diminish as the average velocity of translation, 

 which is fixed l)y the temperature, increases. As the average velocity 

 of translation increases with the temperature, the corpuscles will 

 move more freely under the action of an electric force at low 

 temperatures than at high, and thus from this cause the elec- 

 trical conductivity of metals would increase as the temperature dimin- 

 ishes. In a paper presented to the International Congress of Physics 

 at Paris in the autumn of last year, I described a method by which 

 the number of corpuscles per unit volume and the velocity with 

 which they moved under an electric force can be determined. x\pply- 

 ing this method to the case of bismuth, it appears that at the tempera- 

 ture of 20° C. there are about as many corpuscles in a cubic centimeter 

 as there are molecules in the same volume of a gas at the same tem- 

 perature and at a pressure of about 14 o^ ^^ atmosphere, and that the 

 corpuscles under an electric field of 1 volt per centimeter would travel 

 at the rate of about 70 meters per second. Bismuth is at present the 

 only metal for which the data necessary for the application of this 

 method exists, but experiments are in progress at the Cavendish Labor- 

 atory which it is hoped will furnish the means for applying the method 

 to other metals. We know enough, however, to be sure that the cor- 

 puscles in good conductors, such as gold, silver or copper, must be 

 much more numerous than in bismuth, and that the corpuscular pres- 



