124 
DE. JOULE OjST SOME THEEMO-DTjS'AMIC PEOPEETIES OF SOLIDS. 
111. When the same block was pressed, in a direction perpendicular to the grain, with 
a weight of 1792 lbs. communicated by the lever, a deflection of 37'-3 was produced; 
but when the pressure was removed, the deflection in the reverse direction amounted onl% 
to 31'-2. I believe that the excess in the result of pressure is owing to frictional evolution 
of heat through the imperfect elasticity of wood cut crossways to the grain. The mean. 
34'-25, represents a thermal efi'ect of 0°-0461. Theory gives 
H= 
288-6 
1690 
X 
1792 1 1 1 
1 ^ 20160 ^- 4 ^ 1 - 766 “" 
0°-0261. 
112. A second experiment gave a thermal efiect of 0°-016, the theoretical result being 
0°-0264. In this latter experiment the position of the block was reversed. I attribute 
the discordance between the two results to the difficulty I experienced in obtaining with 
my lever apparatus a perfectly even distribution of pressure over so large a surface as 3 
inches square. 
113. On exposing the block, still crossways to the grain, to a greater pressui-e b) 
means of the hydraulic press, I obtained a deflection of 40'-5, indicating a rise of 0 1 
whenever a weight of 4154 lbs. was laid on, but observed no perceptible effect what- 
ever when the pressure was removed. In this case the bulging of the wood under 
pressure extended to about half an inch. It was evident that frictional heat incieased 
to a great extent the thermal effect of pressure, and that a similar though smaller fl-ic- 
tional effect diminished the cooling effect on removal of pressure. The theoretical 
result, if bulging had not taken place, and supposing perfect elasticitj^ is 
H= 
290 4154 
y ^ __L_ X A X -rf— = 0°-0609. 
^ 1 ^ 20160^ -4 1*766 
1390 
114. Vulcanized India-rubher . — A pillar, 1*92 inch long, 1*22 inch in diameter, and 
weighing 692 grains, had a thermo-electric junction of thin copper and non wires in- 
serted into its centre. On applying pressure, the multiplier showed a rise of temperature, 
and when the pressure was removed, a depression took place, sensibly equal to the pre- 
vious rise. The following is a Table of the results : — 
Weight laid on the pillar, 
in pounds. 
Deflection. 
Heat by laying on the weight, ^ 
or cold by removing it. 
28 
0 / 
3 
6-0058 
33 
3-7 
0-0072 
47 
6-7 
0-0131 
62 
16 
0-0312 
93 
32 
0-0625 I 
124 
i 
1 4-3 
0-1254 i 
With the pressure of 124 lbs. the pillar was compressed to the length 1-05 inch, and 
returned to 1*78 when the weight was removed. 
115. The expansion of the pillar by heat, in the direction in which the pressure was 
applied, was found to be about ^ per degree Cent. Hence the theoretical result for 
a pressure of 124 lbs. would appear to be 
