518 Mr. Phillips on the Slow Stretch in Indiarubber, 



This was done by means of a balance so arranged that the 

 beam was lifted just off the supports. From one end of the 

 beam the scale-pan was removed, and just under this end was 

 placed a heavy weight to which the lower end of a piece of 

 indiarubber bandage was attached by a clip. To the upper 

 end of the bandage a hook was attached by means of another 

 clip. At first the indiarubber was too short to reach to the 

 beam of the balance, but at a certain time it was stretched 

 just far enough to hook on to the beam, and weights were 

 placed in the pan at the opposite end of the beam so as to 

 just balance the pull of the indiarubber. The weight had to 

 be altered from time to time as the stress altered, but as the 

 beam of the balance was only just raised above the supports, 

 the indiarubber was stretched by a practically constant 

 amount all the time. 



The readings in one case were : — 





Time after 





Pull in grams. 



the indiarubber 

 was stretched. 



log*. 



14725 



1 m. 30 s. 



•18 



14675 



2 15 



•35 



1462-5 



3 15 



•51 



1457-5 



4 35 



•66 



1452-5 



7 30 



•88 



1448-5 



10 



100 



1444-5 



14 45 



1-17 



1440-5 



19 24 



1-29 



14365 



26 45 



1-43 



1430-5 



48 



1-68 



1427-5 



58 



1-77 



1412-5 



210 



2-32 



1384-5 



1436 



316 



If the pull be plotted against log t we get a straight line, 

 so that the stress obeys the law 



S = a — Hoe: t. 



From the curve we immediately deduce a to be 1477 grams, 



and the constancy of —, is exhibited in the following 



table. l0 S* 



Little notice should be taken of the first few figures, for 



- S and log t are very small, a 

 measuring S is largely exaggerated. 



a — S and log t are very small, and so a small error in 



