DE. JOULE ON SOME THEEMO-DTNAMIC PEOPEETIES OP SOLIDS. 
115 
order, in wood which is taking up water. It does not immediately assume the length 
due to the state of hygrometry, but if heated the set is taken out, and the wood expands 
to its proper length. 
77. Inasmuch as at a certain degree of humidity wood contracts in every direction 
with a rise of temperature, it might be inferred that on weighing it in water its specific 
gravity would be found to increase on the elevation of temperature. Such, however, is 
not the fact. A piece of saturated wood, being part of the specimen employed in the 
last series of experiments, was found to weigh 392'6 grs. in air, 42'26 grs. in distilled 
water at 0°, and 42 '01 grs. in distilled water at 8°. Hence the cubical expansion was 
•0000892 per degree, but calculated on the wood considered apart from the water in its 
pores, •000396. Therefore on raising the temperature a decrease of specific gravity 
occm's simultaneously with a diminution in the external dimensions of the wood. This 
can only take place in consequence of a contraction of the surfaces of the walls of the 
cellular structure, while the actual bulk of the material of which they are composed is 
increased, a certain minute quantity of water exuding at the same time. 
78. The phenomenon in question is therefore, I believe, owing to capillary attrac- 
tions, which, diminishing with elevation of temperature, has the effect of removing a 
part of the swelled condition due to that action. Dr. Young has given - 5^-5 as the 
descent of water in a narrow tube due to a rise of temperature of 1° Cent. The fraction 
arrived at by M. C. Wolf is To apply the latter estimate to the foregoing- 
results, we find from the last Table that between extreme dryness and perfect humidity 
the wood increased in length from unity to 1’068. Hence, on the hypothesis that the 
contraction by heat is owing to diminution of capillary attraction, it ought to be equal 
to •0001293 minus the expansion in the dry condition. An examination of the fore- 
going Tables will be found to afford ample support to this view. 
79. Itatan Cane . — My observations of the expansion and elasticity of this substance 
are comprised in the following Table. The length exposed to thermal influence was 
33 inches. 
Medium of 
Young’s modulus of 
1 Remarks on the condition 
Weight 
comraunica- 
Limits of tempera- 
Linear contrac- 
elasticity, or length of 
of rod per 
tion of heat 
Tension in 
ture between which 
tion or expan- 
rod, weighing 1 lb. per 
^ of the wood. 
foot in 
between the 
pounds. 
the experiments 
sion per degree 
foot, which would be 
grains. 
glass tube and 
were made. 
Centigrade. 
extended unity by 1 lb. 
i 
the rod. 
tension. 
i 
r 1094242 at 10-6 
Dried by placing it before a 1 
fire for a short time ... J 
150-2 
Mercury ... 
f 35 
191 
25-3 and 11-67 
28-05 and 12-09 
•000024750 E. 
•000027000 E. 
918179 at 34 
956720 at 29 
^ 1048546 at 12 
Wettedbyimmersion under 1 
water for a few hours... j 
208 
Water 
35 
26-6 and 11-04 
•000001436 C. 
Dried by exposure before a 1 
fire for several hours ... J 
145 
Mercury ... 
35 
27^8 and 11-1 
•000016740 E. 
1214179 at 12 
80. The following are the results of my experiments on rose, vine, and poplar. These 
Avere sprouts of recent growth, selected for their straightness. They were cut from 
