Closing Years of the Nineteenth Century. 457 



that at any temperature the ratio of the thermal conductivity 

 of a body to its ohmic conductivity is approximately the same 

 for all metals, and that the value of this ratio is proportional 

 to the absolute temperature. In fact, the conductivity of a 

 pure metal for heat is almost independent of the temperature; 

 while the electric conductivity varies in inverse proportion to 

 the absolute temperature, so that a pure metal as it approaches 

 the absolute zero of temperature tends to assume the character 

 of a perfect conductor. That the two conductivities are closely 

 related was shown to be highly probable by the experiments 

 of Tait^ in which pieces of the same metal were found to exhibit 

 variations in ohmic conductivity exactly parallel to variations 

 in their thermal conductivity. 



The attempt to explain the electrical and thermal properties 

 of metals by aid of the theory of electrons rests on the assump- 

 tion that conduction in metals is more or less similar to 

 conduction in electrolytes ; at any rate, that positive and 

 negative charges drift in opposite directions through the sub- 

 stance of the conductor under the influence of an electric 

 field. It was remarked in 1888 by J. J. Thomson,* who must 

 be regarded as the founder of the modern theory, that the 

 differences which are perceived between metallic and electro- 

 lytic conduction may be referred to special features in the two 

 cases, which do not affect their general resemblance. In 

 electrolytes the carriers are provided only by the salt, which 

 is dispersed throughout a large inert mass of solvent ; whereas 

 in metals it may be supposed that every molecule is capable 

 of furnishing carriers. Thomson, therefore, proposed to regard 

 the current in metals as a series of intermittent discharges, 

 caused by the rearrangement of the constituents of molecular 

 systems a conception similar to that by which Grothussf had 

 pictured conduction in electrolytes. This view would, as he 

 showed, lead to a general explanation of the connexion between 

 thermal and electrical conductivities. 



* J. J. Thomson, Applications of Dynamics to Physics and Chemistry, 1888, 

 p. 296. Cf. also Giese, Ann. d. Phys. xxxvii (1889), p. 576. t Cf. p. 78. 



