56 PROCEEDINGS OP THE AMERICAN ACADEMY. 



Arranging the results in the order of the couductivities of the speci- 

 mens, we get the subjoined table. We call attention to the two groups 

 of fine-grained marbles, which have conductivities of about 0.0068 and 

 0.0076 respectively, at about 30° C. 



Variety of Marble. Conductivity. 



« Carrara Statuary " 0.00501 



0.00509 



« Mexican Onyx " . 0.00556 



" Vermont Statuary " 0.00578 



" American White " 0.00596 



"Egyptian" 0.00623 



"Sienna" 0.00676 



" Bardiglio " 0.00680 



"Vermont Cloudy White" .... 0.00681 



" Vermont Dove Colored " . . . . 0.00684 



"Lisbon" 0.00685 



" American Black " 0.00685 



"Belgian" 0.00755 



" African Rose Ivory " 0.00756 



"Tennessee Fossiliferous" .... 0.00756 



"Knoxville Pink" 0.00757 



" St. Baume " 0.00761 



We reserve for a second paper the results of observations made upon 

 other materials. 



Our acknowledgments are due to the American Academy of Arts and 

 Sciences, which has made an appropriation from the Rumford Fund in 

 aid of our work. 



Jefferson Physical Laboratory, 

 Cambridge, Mass. 



