522 Mr. Phillips on the Slow Stretch in Indiarubber, 



Stretch in 





x— a 



Scale-divisions. 



log*. 



Ioi7' 



289-7 



•38 



2-63 



290-2 



•50 



30 



290-6 



•66 



2-88 



2910 



•86 



2-68 



2913 



•94 



2-77 



291-75 



1-15 



2-66 



292-3 



1-32 



2-73 



292-5 



1-40 



2-72 



292-9 



1-54 



2-73 



293-2 



1-65 



2-73 



293-8 



190 



269 



296'7 



2-92 



2-74 



is the stretch per unit-length and t in minutes, b = 1*55 X 10~\ 

 For a load of 599 kilograms per sq. cm. cross section on the 

 same fibre b was found to be 



1-16x10-*, 



and for a load of 422 kilograms & = *780xl0- 5 . Plotting 

 these three values of b against the load we get a straight line, 

 and when the load is 284 kilograms b becomes 0. This is 

 shown by the approximate equality of the three values of 

 Load- 284 m 



b : 313 xlO 5 



273 X10 5 

 300 xlO 5 



The Slow Stretch in Copper, Platinum, Silver, and 

 Gold Wires. 



It was next thought very desirable to find out whether metals 

 behave in a similar way to glass and indiarubber with regard 

 to slow stretch. 



To investigate this an arrangement almost identical with 

 that used for glass was employed, the rods a being of course 

 replaced by wires of the same kind as that being stretched. 

 Until the load used reached a certain value no slow stretch 

 at all approaching in size to that occurring in glass could be 

 detected, but above this value there was a creep obeying the 

 same law as for the indiarubber and glass. This creep, how- 

 ever, caused a permanent extension, and when the load was 

 removed there was little, if any, slow creep back. 



The inquiry into the slow stretch of wires reveals astonish- 

 ing differences in behaviour, even in specimens from the same 



