On Variation of Thermal Conductivity of Metals, 251 



tricity-motion, as well as for the application of electrical dis- 

 charges to the study of the spectra of gases, is reserved 

 for separate investigations. Meanwhile so much is even now 

 evident, that the different spectra in the parts of different 

 width of discharge-tubes are not to be referred alone to the 

 different temperatures of the gases, but depend essentially 

 upon the amounts of electricity the passage of which condi- 

 tions the oscillatory motions of the aether envelopes of every 

 individual atom or molecule. 



By means of such calorimetric measurements we might in- 

 deed succeed in determining the quantities of heat which are 

 necessary in order so to alter the state of the molecules and 

 atoms that the band spectrum shall change into the line spec- 

 trum ; or, in other words, if we adopt the views developed in 

 the former paper, we must be able to ascertain the amount of 

 heat which is set free at the formation of the molecule of a 

 simple body out of its atoms. 



I shall shortly communicate something further upon these 

 subjects. 



Leipzig, January 1879. 



XLI. On the Determination of the Variation of the Thermal Con- 

 ductivity of Metals with Temperature, by means of the perma- 

 nent Curve of Temperature along a uniform thin Rod heated at 

 one end. By Oliver J. Lodge, D.Sc, Lecturer on Applied 

 Mathematics and Mechanics at University College, London. 



[Concluded from p. 211.] 



Lntroduction of the experimental Values of the Variables into 

 Equation (3) and the first Lntegration of it. 



16. "TYTHAT we have accomplished so far is:— the writing of 



▼ t the fundamental equation (1) by help of equation (2) 



in the form (3), which involves the ratio of rate of cooling 6 to 



k 



thermometric conductivity — ; and then the expression of these 



two quantities as functions of the temperature — the one as a 

 complex function (5), the other as an inverse linear func- 

 tion (4). The latter contains Centigrade temperature t ; but 

 if we reckon temperature from the temperature of the enclo- 

 sure v instead of from the Centigrade zero, it will only affect 

 the value of the constant b. So writing v Q -\-b — 27 4: = m, we 

 get (4) in the form 



k - A - mk o /qx 



cp m + c Q p (m + dy "•••-■• \ J ) 



