240 BODIES SMALLER THAN ATOMS. 



lisions made by a corpuscle in a film will be greater than in the metal 

 in bulk, thus the mobilit}' of the particles in the film will be less and 

 the electrical resistance consequentl}^ greater. 



The corpuscles disseminated through the metal will do more than 

 carr}^ the electric current, they will also carry heat from one part to 

 another of an unequalh' heated piece of metal. For if the corpuscles 

 in one part of the metal have more kinetic energy than those in 

 another, then, in consequence of the collisions of the corpuscles with 

 each other and with the atoms, the kinetic energ}^ will tend to pass 

 from those places where it is greater to those where it is less, and in 

 this way heat will flow from the hot to the cold parts of the metal. As 

 the rate with which the heat is carried will increase Avith the number 

 of corpuscles and with their mobility, it will be influenced by the same 

 circumstances as the conduction of electricity, ^o that good conductors 

 of electricity should also be good conductors of heat. If we calculate 

 the ratio of the thermal to the electric conductivity on the assumption 

 that the whole of the heat is carried by the corpuscles we obtain a 

 value which is of the same order as that found by experiment. 



Wel)er many years ago suggested that the electrical conductivity of 

 metals was due to the motion through them of positively and nega- 

 tivel}^ electrified particles, and this view has recently been greatly 

 extended and developed by Riecke and by Drude. The objection to any 

 electrolytic view of the conduction through metals is that, as in elec- 

 trolysis, the transport of electricity involves the transport of matter, 

 and no evidence of this has been detected. This objection does not 

 apply to the theor}^ sketched above, as on this view it is the corpuscles 

 which carry the current; these are not atoms of the metal, but very 

 much smaller bodies, which are the same for all metals. 



It may be asked, If the corpuscles are disseminated through the 

 metal and moving about in it with an average velocity of about 10^ 

 centimeters per second, how is it that some of them do not escape 

 from the metal into the surrounding air'< We must remember, how- 

 ever, that these negatively electrified corpuscles are attracted by the 

 positively electrified atoms, and in all probability by the neutral atoms 

 as well, so that to escape from these attractions and get free a corpuscle 

 would have to possess a definite amount of energy. If a corpuscle had 

 less energy than this, then, even though projected away from the metal, 

 it would fall Ixick into it after traveling a short distance. When the 

 metal is at a high temperature, as in the case of the incandescent wire, 

 or when it is illuminated by ultra-violet light, some of the corpuscles 

 acquire sufficient energy to escape from the metal and produce electri- 

 fication in the surrounding gas. We might expect, too, that if we could 

 charge a metal so highly with negative electricity that the work done 

 by the electric field on the corpuscle in a distance not greater than the 

 sphere of action of the atoms on the corpuscles was greater than the 



