78 



PROCEEDINGS OF THE AMERICAN ACAD1..MY. 



of melting ice to be 79.25, t lii> corresponds to a conductivity for euch 



slab of 0. 31 1. 



Experiment (6). — Plate A with two thermal elements, enclosed liv 

 two other Bheets of hard rubber, was made into a prism with three plat - 

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



faces of A were 60 .1 and :_' I .9 respectively. In 11,220 set Is 1"»4.8 



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

 between GO and 25° of 0.000311. 



Two other experiments in which the 

 final gradients on the axes of prisms built 

 up of disks about Jo cm. in diameter 

 made of this ruhber wen determined, 

 failed to Bhow any sensible variation of 

 the conductivity with the temperature 

 between 65 and 1G°. 



Experiment (<•>. — A compound slab 

 made of A and a plate, ( '. of the same 

 dimensions as A, hut 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 Btate the indica- 

 tions of the elements on the warm Bide 

 of A, between A and ('. and on the cool 

 side of C, were respectively 69 .8, 11°. 1, 

 and 13°. 1, so that the conductivity of 

 C between 41° and \o° appears to he 

 0.000019. 



After this a number of disks 20 cm. 

 in diameter, which seemed alike in their 

 physical properties, were" cut from the 

 standard rubber and used with other 

 disks to form prisms for the -mailer 

 apparatus. 



Experiments (<h to (o). — By the aid 

 of these standard disks the conductivities of twelve other specimens were 

 easily obtained. [ give in the next table the results, nol in the order 

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

 order of the conductivities of the specimens. 



Figure 3. 



