ON THE CONDUCTIVE POWEES OF VAEIOUS SUBSTANCES. 
813 
and therefore - — -125 
(2) In the next experiment, the two portions of the divided block were cemented 
together with plaster of Paris, applied moist and left to dry and harden, and forming a 
layer of about -^th of an inch in thickness. I thus obtained 
and 
(3) Fine dry powdered clay was 
block. The result was 
and 
then put between the two portions of the divided 
^=• 415 , 
L—t 
(4) Moist clay was then used to cement the two portions of the block, which were 
pressed together for twelve hours. In this case we had 
4 ^^=- 384 , 
and 
^=•069. 
9 
These experiments were made with a temperature nearly equal to that of boiling 
water. To ascertain whether q was independent of the temperature, experiments (3) 
and (4) were repeated at lower temperatures, being about 150°. The first gave 
and the second. 
These values are respectively about one-sixth less than those obtained in experiments 
(3) and (4). They may be considered as corroborating the approximate truth of the 
assumed law that the coefficient q is independent of the temperature, at least when the 
difference of temperature is not too great. 
Hence, then, the values of in the four cases above stated, are 
.(1) 
8, 
p 
(2) 
II 
to 
p 
( 3 ) 
23=10, 
P 
( 4 ) 
^=14. 
P 
5 0 
MDCCCLVII. 
