80 PROCEEDINGS OP THfc AMERICAN ACADEMY. 



Stefan found for the thermal conductivity of a certain sheet of rubber, 

 0.787 cm. thick, the value 0.00026; this rubber had a somewhat greater 

 density (1.22) and a much lower specific heat (0.23) than any of my 

 specimens, so that the ratio of the conductivity to the specific heat per 

 unit volume was somewhat greater. Experimenting upon a thin disk of 

 "ebonite," 1.93 cm, in diameter and 0.0414 cm. thick, Lees determined 

 the conductivity to be 0.000403. 



The Jefferson Physical Laboratory, Harvard University, 

 Cambridge, Mass., July, 1899. 



