456 The Theory of Aether and Electrons in 'the 



If the constants of the metal are such that, for a certain range 

 of values of n, V Z K is small, while v~ (I - K 2 ) is negative, it is evident 

 that, for this range of values of n, v will be small and K large, 

 i.e., the properties of the metal will approach those of ideal 

 .silver.* Finally, for indefinitely great values of n, V~K is small 

 .and v 2 (1 - K 2 ) is nearly unity, so that v tends to unity and K 

 to zero : an approximation to these conditions is realized in 

 the X-rays.f 



In the last years of the nineteenth century, attempts were 

 made to form more definite conceptions regarding the behaviour 

 of electrons within metals. It will be remembered that the 

 original theory of electrons had been proposed by WeberJ for 

 the purpose of explaining the phenomena of electric currents 

 in metallic wires. Weber, however, made but little progress 

 towards an electric theory of metals ; for being concerned 

 chiefly with magneto-electric induction and electromagnetic 

 ponder omotive force, he scarcely brought the metal into the 

 discussion at all, except in the assumption that electrons of 

 opposite signs travel with equal and opposite velocities relative 

 to its substance. The more comprehensive scheme of his 

 successors half a century afterwards aimed at connecting in 

 a unified theory all the known electrical properties of metals, 

 such as the conduction of currents according to Ohm's law, the 

 thermo-electric effects of Seebeck, Peltier, and W. Thomson, 

 the gal vano- magnetic effect of Hall, and other phenomena which 

 will be mentioned subsequently. 



The later investigators, indeed, ranged beyond the group 

 of purely electrical properties, and sought by aid of the theory of 

 electrons to explain the conduction of heat. The principal ground 

 on which this extension was justified was an experimental result 

 obtained in 1853 by G. Wiedemann and K. FranzJ who found 



* Cf. p. 179. 



t Models illustrating the selective reflexion and absorption of light by metallic 

 bodies and by gases were discussed by H. Lamb, Mem. and Proc. Manchester Lit. 

 .and Phil. Soc. xlii (1898), p. 1 ; Proc. Lond. Math. Soc. xxxii (1900), p.. 11 ; Trans. 

 'Camb. Phil. Soc. xviii (1900), p. 348. 



+ Cf. p. 226. Ann. d. Phys. Ixxxix (1853), p. 497. 



