108 DE. JOULE ON SOME THEEMO-DTNAMIC PEOPEETIES OF SOLIDS, 
returned to the same length it had at the commencement of my expei-iments 'inth it. 
™ exactty^d mcheSr^ the thermal effects of stretching rulcanized india-rubber fm a 
greater range of tensions. I inserted a reiy fine thermo-electnc junction into the biead 
S relastic ring 2 inches in diameter and weighing 30 gi-ains. The ring, when pi^ed 
sufficiently to make the two sides paraUel, became a double band 3-3 mches long, whnh 
elongated further to 6'8 inches with a tension of 2i lbs. The res ts amre 
as follow : — - 
Permanent weight 
in pounds. 
Length with 
permanent weight 
in inches. 
Weight laid on in 
addition to the 
permanent weight. 
0 
3-3 
2-5 
2-5 
6-8 
2 
4-5 
11 
2 
6-5 
14-8 
2 
8-5 
17-8 
2 
10-5 
18-9 
2 
12-5 
19-7 
2 
14-5 
20-5 
4 
18-5 
21-1 
2 
20-5 
21-7 
4 
24-5 
22 
4 band broke. 
Length with the 
additional weight. 
Thermal effect 
in 
degree Centigrade. 
6-8 
10-9 
14‘6 
17- 2 
18 - 5 
19 - 4 
20 - 1 
20 - 9 
21 - 3 
22 
Sum , 
0-110 
0-242 
0-330 
0-132 
0-088 
0-068 
0-004 
0-001 
0-009 
0-044 
1-028 
58 The Table shows that the rise of temperature occasioned by stretching i-Jcaimed 
indtrubber bands up to their breaking-point is about !» Centiginde, a quantity which 
I regard as erring somewhat in deficiency, owing to the attenuation of ‘he band 
high tension preventing the full communication of heat to the junction The therm 
elct is evidently greatest when the rubber receives the greatest elongation by » addi- 
flal werght. men the band was stretched to si. times its original eiigth Uttl 
further elongation took place by increasing the tensile force, very httle theimal e e 
being at the same time produced. I thought it possible that m this case a small coo 
effec? might emst, but after many trials did not succeed in findmg it, owing probabl) 
frictional generation of heat near the hreaking-point. 
59 Wood.—Tiie physical properties of this substance hare great m eies -om 
valLTpplications to L wants and luxuries of mankhid. On making expei— n 
the thermal effects of its extension and compression, I soon found anomalies wine 
nducerme to investigate at some length its expansion by heat, its elasticity and 
variations of these ai'islng from such modifying influences as teniperatui-e, moistiue. 
‘Tq“”Tbe annai-atus I employed will be understood from the foUon-ing sketch, in 
whffih f wotden rod is represented as passing through a glass tube, which agani 
passes through a wide tube of gutta percha. This latter fits tightly at its lowei e 
L the glass tube, which again is made tight to the wood by means of a piece of indi. - 
