78 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



of melting ice to be 79.25, this corresponds to a conductivity for each 

 slab of 0.000311. 



Experiment (b). — Plate A with two thermal elements, enclosed by- 

 two other sheets of hard rubber, was made into a prism with three plates 

 of glass. In the final state the temperatures of the elements on the 

 faces of A were 60°. 1 and 24°. 9 respectively. In 11,220 seconds 154.8 

 grams of ice were melted. This again corresponds to a conductivity 

 between 60° and 25° of 0.000311. 



Two other experiments in which the 

 final gradients on the axes of prisms built 

 lip of disks about 20 cm. in diameter 

 made of this rubber were determined, 

 failed to show any sensible variation of 

 the conductivity with the temperature 

 between 65" and 16°. 



Experiment (c). — A compound slab 

 made of A and a plate, C, of the same 

 dimensions as A, but purporting to come 

 from another maker, with their thermal 

 elements and " guard plates " of rubber, 

 were used to form a prism for the large 

 apparatus. In the final state the indica- 

 tions of the elements on the warm side 

 of A, between A and C, and on the cool 

 side of C, were respectively 69°. 8, 41°. 1, 

 and 13°. 1, so that the conductivity of 

 C between 41° and 13° appears to be 

 0.000319. 



After this a number of disks 20 cm. 

 in diameter, which seemed alike in their 

 physical i:»roperties, were cut from the 

 standard rubber and used with other 

 disks to form prisms for the smaller 

 apparatus. 



Experiments (d) to (p). — By the aid 

 of these standard disks the conductivities of twelve other specimens were 

 easily obtained. I give in the next table the results, not in the order 

 in which the experiments were performed, but, for convenience; in the 

 order of the conductivities of the specimens. 



Figure 3. 



