278 
ON THE RIGIDITY 
TABLE I. 
Dame. | Tear | pene) mae | oe | Rene ater | 
| (degrees.) 
Oo#OOL aE a eos Nees | fae ee 1.611 
935.) 17/5) |). AGr82"| se322 aieasOIT || 0209): 68 “ 
94) 17-4 ; 49.68; .3137', 1013 | 0209 |, 62. ))eemien 
, 96,,! 91.4 | 62.98 | -.308 1 625 | 0117 | 69, (| Saxaae 
« 96..| 20.5 | 53.07] .302 | 1093 | .0209 | ‘71 “ 
 97.., 19.5 | 56.981 .201 | 1235 | 0209 | 78 | s3aiy 
ff 30: S54 Bieee| ete se) O17 || aia x 
¢ 30..| 18.8 | 57.281 .201 | 1256 | .0209 78 és 
ea 31.178, (Gles2 | 2¥S" | tors | 20209), | 702 ean 
Nov. 1..| 19.5 | 66.88] .270 | 1545 | .0209 | 99 | 4.289 
| | 
Although the above table shows considerable disagreement 
between successive observations, due probably in some measure 
to friction, to difference of temperature slightly, and to 
inequality in the times of application of the loads, the values 
obtained clearly increase with the tension, and give no indication 
of a minimum point. This result is in agreement with Mr. Mac- 
donald’s Jast series of observations, and seems to show that the 
rigidity increases steadily with tension in a cord which has 
been subjected to sufficiently prolonged extension, provided at 
least a day is allowed to intervene between increasing the ten- 
sion and determining the rigidity. 
made on a fresh cord of a 
Macdonald’s. 
The next observations were 
Mr. It was harder, and 
contained 60 per cent of pure rubber, according to the state- 
ment of the manufacturer. A freshly-cut surface showed a 
different rubber from 
dark gray colour. 
All the series of observations given below were made on 
rubber cords of this kind. 
Both static and kinetic methods were applied, very little 
time being allowed to intervene between the two determina- 
tions, in order that the cord might be in the same state, as 
