162 Lord Kelvin and Mr. J. R. Erskine Murray. [May 30, 



May 30, 1895. 

 The LORD KELVIN, D.C.L., LL.D., President, in the Chair. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



In pursuance of notice sent to the Fellows, an election was held to 

 fill the vacancj upon the Council occasioned by the retirement of 

 Professor A. H. Green. 



The Statutes relating to the election of the Council and the Statute 

 relating to the election of a Member of Council upon the occurrence of 

 a vacancy were read, and Dr. Armstrong and Mr. R. H. Scott having 

 been, with the consent of the Society, nominated Scrutators, the votes 

 of the Fellows present were taken and the Rev. Thomas George 

 Bonney was declared duly elected. 



The following Papers were read : 



1. "On the Temperature Variation of the Thermal Conduc- 

 tivity of Rocks." By LORD KELVIN, P.R.S., and J. R. 

 ERSKINE MURRAY, B.Sc.", 1851 Exhibition Scholar. Re- 

 ceived May 24, 1895. 



1. The experiments described in this communication were under- 

 taken for the purpose of finding temperature variation of thermal 

 conductivity of some of the more important rocks of the earth's crust. 



2. The method which we adopted was to measure, by aid of 

 thermoelectric junctions, the temperatures at different points of a flux 

 line in a solid, kept unequally heated by sources (positive and nega- 

 tive) applied to its surface, and maintained uniform for a sufficiently 

 long time to cause the temperature to be as nearly constant at every 

 point as we could arrange for. The shape of the solid and the 

 thermal sources were arranged to cause the flux lines to be, as nearly 

 as possible, parallel straight lines ; so that, according to Fourier's 

 elementary theory and definition of thermal conductivity, we should 



have 



KM, B) _ |>(M)-i;(T)]-i-MT 

 &(T, M; KB) u(M)]-4-BM ' 



where T, M, B denote three points in a stream line (respectively next 

 to the top, at the middle, and next to the bottom in the slabs and 

 columns which we used) ; v(T), v(M~), v(B) denote the steady tern- 



