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University of California Publications. [Geology 



tional to the distance from the point source of the heat to the 

 point whose temperature is under consideration. 



We have, then, for one direction, It =K/d-s; 



and for another direction, Tc'=K' /d-s; 



and, since density and specific gravity are not directed quanti- 

 ties, and are constants for any one specimen, we have k:k'= 

 K:K'. 



The rest of Senarmont's question was first answered by Duha- 

 mel* on the basis of a theory which he had worked out in 1828. 

 The foundation of this theory was the hypothesis that heat is 

 conducted within a solid body by radiation from one molecule to 

 another. Duhamel came to the conclusion that the ratios of the 

 axes of an isothermal ellipsoid are equal to the ratios of the 

 square roots of the thermometric, and hence also thermal, con- 

 ductivities in the corresponding" directions. 



In the same year, G. G. Stokesf came to the same conclusion 

 from a perfectly general discussion of the conduction of heat in 

 crystals, in which no assumption was made as to intermolecular 

 radiation or any other means by which the heat might be con- 

 ducted. His differential heat equations and the beautiful line 

 of reasoning by which he finally gets his result would be out of 

 place in this paper. His result is that the axes of the ellipse 

 are proportional to the square roots of the thermal conductivi- 

 ties, and accurately so, for the shape of the ellipse is unaffected 

 by the losses from the surface. 



The removal of the theoretical difficulties which had pre- 

 vented the interpretation of the laboratory results, at once gave 

 good opportunities for satisfactory research work. 



E. JannetazJ found that boring holes into the sections was 

 a tedious and unsatisfactory business, so he used a small 

 platinum bullet through which he sent an electric current by 



* J. M. Duhamel. Sur les equations generales de la propagation de la 

 chaleur dans les corps solides dont la eonductibilite n 'est pas la meme dans 

 tons les sens. Jour, de l'eeole polyteeh. 13, 356, 1832. 



t G. G. Stokes. On the conduction of Heat in crystals. Cambridge and 

 Dublin Math. Journal. 6, 215, 1851. 



t E. Jannetaz. Des Surfaces Isothermes en mineralogie et en geologic 

 Notice sur les travaux scient. de M. E. Jannetaz. Meulan, 1882. 



E. Jannetaz. Sur la propagation de la chaleur dans les corps cristallises. 

 Annal chim. phys. (4) 29, p. 5, 1873. Bull. Soc. Geol. de France, 1873- 

 1878; 1881. Journ. de Physique, (1) 5, pp. 150, 247, 1876. 



