THE 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XLVIII. FOURTH SERIES. 



LXV. The Heat -conducting Power of Mercury independent of the 

 Temperature. By Hermann Herwig*. 



ACCORDING to a proposition enunciated by Wiedemann 

 and Franz f, the metals have an approximately equal con- 

 ducting-power for electricity and heat. Now it would be of the 

 greatest importance to know if the correspondence between the 

 two conducting-powers is perfect, and especially whether it sub- 

 sists under all temperatures. If we wish to institute investiga- 

 tions in this direction, we must, in regard to their practicability, 

 distinguish two things. The first portion of the problem, to 

 demonstrate the exact equality of the two powers of any metal 

 at a determined temperature, is attended with the great difficulty 

 of obtaining metals perfectly homogeneous and, above all, unal- 

 tered by the experiments themselves. On the other hand, the 

 influence of temperature on the conducting-powers offers far 

 more favourable conditions for an investigation. From nume- 

 rous experiments, especially those made by ArndtsenJ, and 

 by Matthiessen and Von Bose §, it is known that, for the electric 

 conductivity, a very marked variability with the temperature 

 takes place, and indeed, for by far the greater number of metals, 

 in not very different degrees. There must, accordingly, if the 

 correspondence made known by Wiedemann and Franz were 

 really so widely valid, be found also for the heat-conducting 

 power of most metals a variability with temperature in about the 

 same degree ; and therein not only somewhat different qualities 

 of the same metal, but, as has been said, quite different metals 

 would be fairly equivalent. This side of the question is therefore 

 very suitable for investigation, and it also appears to me to touch 

 most deeply the essence of the entire ques'.ion. 



* Translated from a separate impression, communicated by the Author, 

 from Poggendorff's Annalen, vol. cli. pp. 177-1^4. 



t Pogg- Ann. vol. lxxxix. p. 531. % Ibid. vol. civ. p. 56. 



§ Ibid. vol. cxv. p. 38!). Phil. Mag. S. 4. vol. xxiv. p. 406, 



Phil. Mag. S. 4. No. 321. SuppL Vol. 48. 2 I 



