to which observations of the kind alluded to have been extended. 

 The author was led to a careful examination of the existing deter- 

 niinations of the conducting powers of the metals for heat, by some 

 collateral trains of experiment in which he was occupied two years 

 ago. He points out the degree of confidence which may be placed 

 in the arrangement of conductors given by different authors ; for 

 we appear to be far fi-om reaching a correct estimate of their nu- 

 merical values. In viewing those of M. Despretz as the best, he 

 remarks, that the position of platinum, which is certainly errone- 

 ous, shews how insperfectly we can depend upon experiments on 

 this point, made with even more than usual care. Platinum is 

 placed by this writer almost at the top of the list, between gold 

 and silver, whilst the commonest experiments serve to shew that 

 it is really a very imperfect conductor. 



In order to verify the conclusions of previous observers, and to 

 determine the position of some metals upon which no experiments 

 seem to have been made, the author employed Fourier's Thermo- 

 meter of Contact, an elegant instrument, which he believes has not 

 before been practically applied. His experiments, however, being 

 only intended for the illustration of a subject of collateral inquiry, 

 were not made with the detail that they would otherwise have 

 been, nor are they presumed to be perfectly accurate. They 

 served, however, to confirm previous experiments on the order of 

 the metals as conducting substances ; to restore platinum to its 

 right place, and to fix the positions of antimony and bismuth. 

 From these and other data, he considers the following as the most 

 probable arrangement of conductors of heat, beginning with the 

 best : — Gold, Silver, Copper, Brass, Iron, Zinc, Platinum, Tin, 

 Lead, Antimony, and Bismuth. 



In like manner, by a careful comparison of the results of Harris, 

 Becquei el, and Pouillet, including some experiments on antimony 

 and bismuth, made at the author's request by Mr Harris, he con- 

 cludes, that the arrangement of the metals as conductors of elec- 

 tricity it the following, which he observes is probably better esta- 

 blished than the corresponding one for heat : — Silver, Copper, 

 Gold, Zinc, Brass, Iron, Platinum, Tin, Lead, Antimony, and 

 Bismuth. He observes, that the deviations from a common ar- 

 rangement only occur where it is agreed, by experiments on both 

 points, that the metals are extremely closely allied ; as, for exam- 



