Royal Society. 467 



only to motion due to the action of the second hemispherical 

 surface. 



Having brought the argument to this point, I reserve for the 

 next communication the deduction of inferences from the above 

 equation, and the application of results to the Theory of the Dis- 

 persion of Light. 



Cambridge, May 18, 1864. 



LXXI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 387-] 

 June 18, 1863,-^Major-General Sabine, President, in the Chair. 

 ^l^HE following communications were read : — 

 -*- " On the Influence of Temperature on the Electric Conducting- 

 Power of Alloys." By A. Matthiessen, F.R.S., and C. Vogt, Ph.D. 

 The subject of this paper has been divided into four parts, viz. : — 



I. Experiments on the influence of temperature on the electric 

 conducting-power of alloys composed of two metals. 



II. Experiments on the influence of temperature on the electric 

 conducting-power of some alloys composed of three metals. 



III. On a method by which the conducting-power of a pure 

 metal may be deduced from that of the impure one. 



IV. Miscellaneous and general remarks. 



In the first part, after having given the numerical results, we 

 proceed to explain the law which regulates this property. It is as 

 follows : — 



The observed percentage decrement in the conducting-power of an 

 alloy between 0° and 100° C. is to that calculated between 0° and 

 100° C. as the observed conducting-power at 100° C. is to that cal- 

 culated at 100° C. 



Or in symbols, Po : Pc : : X 10QO : X' l0QO , 



where Po and Pc represent the observed and calculated percentage 

 decrements in the conducting-power of the alloy between 0° and 

 100° C. ; and X and X' its observed and calculated conducting- 

 power at 100° C, Pe is equal in nearly all cases to 29*307*, the 

 exceptions being only in the instances of thallium and iron alloysf. 



The above law holds good for most of the alloys belonging to the 

 first and third groups, as well as for a part of those belonging to the 

 second group J. 



Now, if the above proportion, 



Po:Pc::A I00O :X V> ....... (1) 



be converted into terms of resistance, the following formula is 

 obtained, r^-r^r'^-r'^, (2) 



'ioo ' r o ' r 'ioo°' an( * r 'o° re P resent the observed and calculated 

 * Phil. Trans. 1862. f Phil. Mag. S. 4. vol. xxvi. p. 542. 



$ Phil. Trans. 18G0, p. 161. 



2H2 



