80 PROCEEDINGS OF THE AMERICAN A.CADEMY. 



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Stefaa fouud for the thermal conductivity of a certain Bheet of rubber, 

 7 cm. thick, the value 0.00026 ; this rubber bad a somewhat j^n-ater 

 density (1.22) and a much lower Bpecific heal (0.28) than any of my 

 specimens, bo that the ratio of the conductivity to the Bpecific heat per 

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

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

 the conductivity to be 0.000403. 



Thb Jefferson Physicai Laboratory, Harvard University, 

 Cambridge, Mass., .July, L899 



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