106 
DE. JOULE ON SOME THEEMO-DTNAMIC PEOPEETIES OP SOLIDS. 
Tensile 
force in 
pounds. 
14 
Temperature 
successively 
raised. 
Length 
in inches. 
Temperature 
successively 
lowered. 
Length. 
; Mean tempe- 
I rature of the 
I two series. 
13-4 
4-899 
9-2 i 5-008 
O 
11-3 
22-5 
4-894 
21-5 1 4-979 
22 
32 
4-888 
30-8 4-952 
31-4 
48-6 
4-888 

48-6 
Mean 
length. 
4-953 
4-936 
4-920 
4-888 
Shortening 
per degree 
Cent, from 0^ 
51. The above results completely justify the anticipation of Professor Thomson, and. 
as we shall presently see, afford a remarkable confirmation of his theory. Before, how- 
ever, instituting a comparison between theory and experiment, it ^viU be pioper to 
observe that the length of the rubber at the low temperatm-es beginnmg and endmg eac i 
experiment show a gradual elongation. To this circumstance chiefly is it owing that so 
considerable a shortening effect took place with 7 lbs. tension ; for a tensile force o 
14 lbs having been just previously tried, a certain amount of mcreased lengt o e 
nature of set was produced, which being taken out by heatmg the rubber under less 
tension, caused a greater apparent contraction by heat. On lowering the temperature 
again, a small contraction took place, which, being corrected for the gradual elongation 
of the rubber, gave me Wo 9 a® the expansion by heat under the tension of / bs. 
52. The following Table gives the theoretical estimate, compai-ed with the experi- 
mental result, for each additional tensile force of 7 lbs. 
