DE. JOULE ON SOME THEEMO-DYNAMIC PEOPEETIES OF SOLIDS. 
117 
83. It will be observed that an increase in the expansibility by heat of paper and 
leather was produced by moisture. It is probable, however, that had they been more 
thoroughly saturated, the expansion would again diminish, as in the case of wood cut 
across the grain, in which, although the expansibility in the first instance increased with 
the application of moisture, it ultimately changed into contraction when the wood 
became more completely saturated. I think that a cause tending to increase the expansi- 
bility in consequence of the application of moisture exists in every case ; but that it is 
modified, and in wood sometimes completely overcome, by the effect of decreased capil- 
lary attraction with rise of temperature, to which I have already adverted, 
84. Upon the facility with which hot moistened whalebone can be moulded into 
form, and the permanency with which it keeps the shape in which it is cooled, much of 
its use in the arts depends. When heat is applied to whalebone, thus cooled in a con- 
strained state, it at once returns to its original shape. Even when cold moistened whale- 
bone is strained, it returns almost immediately to its original dimensions on the appli- 
cation of heat. The slip of moistened whalebone employed in the exj)eriments recorded 
in the last Table, 46 inches long and weighing 71 '8 grains to the foot, became rapidly 
stretched 7 inches longer by a tension of 64 lbs. Left to itself after the tensile force was 
removed, it began to return gradually towards its original length, which however it at 
once assumed on immersion in hot water. 
86. The apparent elasticity of whalebone is always somewhat less than the real, owing 
to the observed elongation, when tension is applied, consisting of a considerable amount 
of set as well as of elastic strain. Also when the tensile- force is removed, the contrac- 
tion which takes place consists of the return from set as well as of the elastic recoil. 
The interesting phenomena connected with imperfect elasticity might, I think, be very 
advantageously studied in this substance. The limits I had set myself did not, however, 
allow me to do more than obtain the following determinations of its elasticity in the 
dry state at two different temperatures, and with various intervals between the applica- 
tion or removal of tension and the corresponding observations. 
Time allowed to 
elapse between laying 
on or taking otf a 
tensile force of 35 lbs., 
and making the ob- 
servation of length. 
Young’s modulus of apparent elasticity, 
or length of rod, weighing 1 lb. per foot, which 
would be extended unity by 1 lb. tension. 
At 
At 30“-l. 
15" 
1176554 
962450 1 
30" 
1147383 
927100 
1' 
1119624 
894545 
2' 
1080415 
! 
4' 
1043860 
15' 
1028395 
U 
922481 
86. Thermal effect of tension on Wood . — My first experiment was tried on a square rod 
of straight-grained pine, dried, and weighing 132’4 grains to the foot. A thermo-electric 
junction of thin copper and iron wires having been inserted into it, its upper extremity 
MDCCCLIX. T? 
