ON THE CONDUCTIVE POWEES OF VAEIOUS SUBSTANCES. 
809 
4. Influence of Pressure. 
(1) A block of spermaceti, solidified under a pressure of 850 lbs. per square inch, 
gave 
-=•086. 
c 
Another block, solidified under a pressure of 7500 lbs. per square inch, gave so nearly 
the same value as only to admit the conclusion that pressure had no sensible infiuence 
on the conductive power of this substance. 
Instead of taking blocks solidified under the above pressures, I took another com- 
pressed, after solidification, rvfith a weight of 7500 lbs. per square inch. The result was 
identical with that obtained from the block solidified under the same pressure. 
(2) Wax. — This substance, when uncompressed, gave 
-=•072, 
c 
and when compressed by a pressure of 7500 lbs. per square inch, 
-=•079. 
c 
The increase is too small to exceed the probable limits of error. 
(3) Clay. — The results in this case were as follows: — 
-=•20 
C 
Uncompressed clay 
Compressed with a weight of 4300 lbs. per square inch 
Compressed Avith a weight of 7500 lbs. per square inch 
Here we have a considerable increase due to pressure. 
(4) Chalk. — No appreciable increase of conducthity was observed in this case with 
pressures equal to those above cited. 
(5) Mixture of sand and clay: — 
- = •30 
c 
-=•33 
c 
Compressed with a weight of 4300 lbs. per square inch 
Compressed with a weight of 7500 lbs. per square inch 
= •36 
^ = •378 
c 
5. Influence of Temperature. 
The experiments for determining the infiuence of temperature were confined to two 
substances which melt at low temperatures, bees’-wax and spermaceti. Denoting the 
temperatures of the lower and upper surfaces of the blocks respectively by t^ and C? I 
obtained the following results : — 
C = 105°-3| 
C= 85°-6J’ 
^ = •088 
c 
