852 



LORD KELVIN. 



with only this différence, that the metallic atom must be so crowded 

 with electrions that some of them are always being spilt out of each 

 atom by the interinolecular and electrionic thermal motions, not only 

 at ordinary atmospheric températures, and higher, but even at tempe- 

 ratures of less than 16° Centigrade above the absolute zéro of tempe- 

 rature. I say 16° because in Dewar s Bakerian Lecture to the Eoyal 

 Society of London, June, 13, 1901, „The Nadir of Température", we 

 find that platinum, gold, silver, copper and iron have exceedingly high 

 electric conductivity at the température of liquid hydrogen boiling 

 under 30 mms. of mercury, which must be something between 20°5, 

 the boiling point of hydrogen at 760 mms. pressure, and 16°, the tem- 

 pérature of melting solid hydrogen, both determined by Dewar with 

 his hélium thermometer. There is no difficulty in believing that the 

 electrions in each of the metallic atoms are so numerous that though 

 they rest in stable equilibrium within the atoms, closely packed to 

 constitute the solid métal at 0° absolute, and may move about within 

 the atom with their wildly irregular thermal motions at 1° of absolute 

 température, they may between 1° and 2° begin to spill from atom to 

 atom. Thus, like glass or a Nkrnst filament below 300° absolute, a 

 métal may be an almost perfect insulator of electricity below 1° abso- 

 lute : may, like glass at 333° absolute, show very notable conductivity 

 at 2° absolute: and, like glass at 473" absolute as compared with glass 

 at 333° absolute, may show 8000 times as much electric conductivity 

 at 2°-8 as at 2°. And, like the Nernst filament at 1800° or 2000° 

 absolute, our hypothetical métal may at 6° absolute show high conduc- 

 tivity, comparable with that of lead or copper at ordinary températures. 

 The electric conductivity in the Nernst filament goes on increasing as 

 the température risestill the filament melts or évaporâtes. Nevertheless it 

 is quiteconceivable that in our hypothetical métal with rising température 

 from 2° to 16° absolute the electric conductivity may corne to a maxi- 

 mum and decrease with further lise of température up to and beyond 

 ordinary atmospheric températures. In fact, while some extent of ther- 

 mal motions is necessary for electric conductivity, too much of thèse 

 motions must mar the freedom with which an electrion can thread its way 

 through the crowd of atoms to perform the function of electric con- 

 duction. It seems certain that this is the matter-of-fact explanation 

 of the diminution of electric conductivity in metals with rise of tem- 

 pérature. 



