CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL LABORATORY, 



HARVARD COLLEGE. 



ON THE THERMAL CONDUCTIVITIES OF CERTAIN 



PIECES OF ROCK FROM THE CALUMET 



AND IIECLA MINE. 



By B. O. Peirce. 



Presented April 8, 1903. Received April 9, 1903. 



Several years ago Dr. R. W. Willson and I presented to the Acad- 

 emy an account of some measurements of the conductivity for heat of 

 several kinds of marble, and we discussed at that time * the theory of our 

 method and described the apparatus we employed in our work. This 

 present paper gives the results of determinations, by the same method, of 

 the thermal conductivities of six representative slabs of rock from the 

 Calumet and Hecla mine, very kindly lent to me by Professor Alex- 

 auder Agassiz. These conductivities are interesting in view of the fact 

 that the rate of increase of mean annual temperature with the depth 

 seems to be very unusually small near the shaft where Dr. Agassiz's 

 measurements were made. 



Each of the slabs is a rectangular parallelopiped about four inches 

 thick and two feet scpiare : their average weight is a little over two 

 hundred pounds. There are two specimens of trap, two of amygdaloid, 

 and two of conglomerate. Each of the pieces of trap seems very homo- 

 geneous, and each piece of amygdaloid sutliciently so to make the result 

 of each measurement an excellent determination of the mean conductivity 

 of the slab in question : in the case of conglomerate, some variations in 

 conductivity are, of course, to be expected in different parts of any large 

 piece ; I hope, however, that the figures given below represent with some 

 accuracy the average conductivities of the slabs examined. The deter- 

 minations involved steady work for several months. 



The size of the blocks to be experimented on made some slight modi- 



♦ These Proceedings, August, 1898. Vol. XXX IV. 1. 



