76 



PROCKKIUNi;- OF THE AMERICAN ACADEMY. 



The present paper describes :i Beries of experiments on the thermal 

 conductivities of differenl specimens of hard rubber,* or " vulcanite," 

 made by tin- method which we described at length last year. 



I had at in v disposal fourteen different pieces of hard rubber thick 

 enough to he used conveniently in the apparatus, ami much of this \\ r as 

 in sheets about L20 cm. by 50 cm. So much of it as was bought for the 

 purposes of this investigation came from three well known makers. 

 Besides this new rubber, however, there were a number ol pieces from 



Figure 2. 



unknown sources, which had been lying in the laboratory for indefinite 

 periods. The specific gravities of the different specimens examined 

 differed slightly from each other, hut by not nearly so much as one per 

 cent in the extreme cases. The specific gravity of the rubber used as a 

 standard is about L.202, and its average specific heat hetweeu •_'"» ('. and 

 100° C. is 0.339. The specific heat of sheet ruhher usually increases 

 with the temperature, as may be inferred from the subjoined table, in 



* Stefan, Sitzungsberichte <lcr Wiener Akailemic <ler Wissenechaften, 1876; 

 Lees. Philosophical Transactions, 18'.»;). 



