LONDON, ED^$!^h|(nd DUBLIN 



PHILOSOPlj|^^MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



MARCH 1846. 



XXX. On the Determination of the Temperature and Con- 

 ducting Power of Solid Bodies. By Chr. Langberg of 

 Christiania *. 



TVTOTWITHSTANDING the important progress which 

 -^ has been made in the mathematical theory of the phe- 

 nomena of heat by the analytical researches of Fourier, Pois- 

 son and others, it is not to be denied that the influence which 

 these have exerted upon the extension of our physical know- 

 ledge of the phaenomena is very limited, and that only a few 

 of the results obtained from mathematical theory have been 

 demonstrated and proved by experiment. The reason of this 

 is in a great measure owing to the want of accurate modes of 

 ascertaining changes of temperature in solid bodies, without 

 militating against too many of the conditions required by the 

 mathematical theory. 



Thus we are taught by mathematical analysis that one of the 

 most important elements in the theory of heat, namely the con- 

 ducting power of solids, can be ascertained by placing in con- 

 nexion with a constant source of heat the end of a long, thin, 

 homogeneous, cylindrical or prismatical rod, composed of the 

 substance to be examined, and observing the temperature of 

 this rod at different distances from the heated end ; the differ- 

 ence between the observed temperatures on the rod and that of 

 the surrounding air decreases in geometrical progression when 

 the points of observation are at equal distances from each other. 



For establishing these laws experiments have been instituted 

 by Biotfj and more lately by Despretz \ ; those of the latter 



* Being an abstract from Poggendorff's Annalen, 1845, No. 9; commu- 

 nicated by Dr. Ronalds. 



\ Traite de Physique, torn. iv. p. 670. 



j Annates de Chimie et de Physique, torn, xxxvi. p. 422. Traite Elhnen- 

 taire de Physique, p. 210. 



Phil. Mag. S. S. Vol. 28. No. 186. March 1 846. N 



