C 147 ] 



XVI. Note on Thermal Conductivity, and on the Effects of 

 Temperature-Changes of Specific Heat and Conductivity on 

 the Propagation of Plane Heat-Waves. By Professor 

 Tait *. 



IN the great majority, at least, of investigations (experi- 

 mental or mathematical) connected with conduction of 

 heat, it has been assumed that the known changes of specific 

 heat of metals do not require to be taken into account. Thus 



o 



Angstrom says, even in his paper on the Change of Conducti- 

 vity with temperature (Pogg. ^wn.cxviii. 1863): — " Da indess 

 diese Veranderungen, soweit man sie kennt, wenigstens in- 

 nerhalb der bei den Beobachtungen vorkommenden Tem- 



peraturgranzen, nicht bedeutend sind, so mussen 



dieselben den Werth des Warmecoefficienten nur unbedeu- 

 tend afficiren konnen." In my paper on " Thermal and 

 Electric Conductivity" (Trans. R. S. E., 1878), I said that 

 " the change of specific heat with temperature would increase 

 the values of k at higher temperatures, and thus reduce the 

 change in conductivity in iron, and increase the small changes 

 indicated for the other substances." But I had not at hand 

 the means of applying these corrections. Recent discussions 

 as to the comparative merits of different experimental methods 

 have led me to investigate the amount of this effect, by the 

 aid of the best data I could procure. A comparison of these 

 seems to leave no doubt that the specific heat of iron increases 

 by somewhere about t ^q of its amount for each degree of 

 rise of temperature, at least from 0° to 300° C, between 

 which limits the investigations of conductivity have hitherto 

 been carried on. 



Besides this result, which I have gathered from various 

 scientific journals, I may adduce from my laboratory book 

 for 1868 the following determinations, which were made with 

 great care by the late Mr. J. P. Nichol, by means of the 

 method of mixtures. The nature of the process employed is 

 such that the results must all err in defect, and the more so 

 the higher the temperature. The iron was heated sometimes 

 in oil, sometimes in paraffin. 



* From the Proceedings of the Koyal Society of Edinburgh, 17th 

 January and 7th February, 1881. Communicated by the Author. 



