illustrated by the Behaviour of Electric Vacuum Valves. 7 



carrying power of positive and negative ions will be equal : 

 that is to say, neu will be the same for both. And, since e 

 is undoubtedly the same for both, this means that raz = NU, 



7X1111 t 7111L 



while the ratio of their aggregate energies, „„ n2 = vjyt» 



is the same as the ratio of their individual momenta. 



If the same propelling force acts on both sets for the same 



time, it may be supposed that the individual momenta are 



, TP n U m 

 equal. It so, ^ = — = rrj-. 



Now if the gas be (say) nitrogen, the ratio of the mass of 

 an atom to that of an electron is M/m=14 x 1700 = 23,800; 

 or the speed of the atoms is less than the twenty thousandth 

 of that of the electrons, though the}^ are more than twenty 

 thousand times as numerous. 



But though the individual momenta of opposing bodies — 

 electrons and atoms — are equal, so that they can stop each 

 other on collision, it is plain that the aggregate electronic 

 momentum is the smaller of the two, and that matters can 

 be so arranged that a large part of it can be absorbed close 

 to the cathode, or can be coaxed into regions, such as the 

 interior of hollow spaces, where its violence will be mecha- 

 nically inoperative, while a fairly unobstructed path is left to 

 the effective carriers ; and this is what is arranged in an easy 

 tube, or in the easy direction of a valve. 



Although the positive carriers are spoken of as compa- 

 ratively leisurel\ r , it is not to be supposed that they are what 

 in ordinary speech is called " slow/' Their speed appears to 

 be of the order of a kilometre per second. 



General Remarks. 



Incidentally it may be worth explicitly noting that whereas 

 in vacuum-tubes the positively-charged atoms are the main 

 conveyers of the current, in metals the conduction is almost 

 certainly due to the free migration of electrons ; while in 

 liquid electrolytes the conduction is distributed in approxi- 

 mately equal proportions, or rather in perfectly known nume- 

 rical proportions, between the positive and negative ions. 



The fact that the conveyers of electricity have to change 

 in sign when a current passes from a metal to a gas, or 

 vice versa, which exchange can only be effected by a neutrali- 

 zation or combination of the opposite charges at the bounding 

 surface, suffices to account for some of the heat which is there 

 developed. 



University of Birmingham. 



