6 Schwartz & Kemp, Physical Properties of Rubber. 



reverse action with weak tensile forces did not take place, 

 but that there was, on the contrary, a very shght heating 

 effect." Fig. i is a diagram of his apparatus, reproduced 

 from his original papers. The experiments performed by 

 the authors were conducted at the temperature of melting 

 ice, in order to secure the advantages of constancy which 

 can be thus obtained. 



Fig. I. Joule's Apparatus. 



The method of measuring the temperature employed 

 by the authors was substantially the same as that used 

 by Joule, namely, by means of a thermo-junction inserted 

 in a longitudinal slit near the middle of the specimen. 

 The differences in detail consisted in the use of a single 

 pair of copper and iron wires in the case of Joule, and 

 ten pairs of copper-eureka junctions used with a sensitive 



