658 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



was assumed to be 126.70 sq. cm. : this includes a slight correction for the 

 thickness of the brass walls. The latent heat h of melting ice was as- 

 sumed to be 79.25. 

 If, then, 



r =. rate of melting of ice in the pot, in grams per second, 

 t —■ temperature of difference between the faces of the slab, 

 d= thickness of the slab, 

 k = mean thermal conductivity of the slab, 



k = 



r • d • h 



t ' a 



TABLE I. 



Table I gives some of the data of my final determinations. It would 

 have been easy to give the value of k with greater apparent accuracy, 

 but, in view of the lack of homogeneity in some of the slabs, this would 

 have been misleading. The trustworthiness of results obtained with the 

 apparatus described above is discussed in these Proceedings for August, 

 1898. 



Table II shows the results of other determinations of the thermal 

 conductivities of different specimens of rock. Many of these, as will be 

 seen, were made by Messrs. Herschel, Lebour, and Dunn for the British 

 Association for the Advancement of .Science. The names of the dif- 



