042 Prof. Trouton and Mr. Rankine: Stretching and 
vey nearly those that would be expected from the equation 
) G=28°3—12°9 logt. 
Tf this equation truly represents the rate of decrease, then 
it would mean that the couple immediately after the twist 
is produced is infinite. It is therefore more probable that 
the curve, if exponential at all, is so to an axis = — (a small 
quantity), instead of t=0. It would be difficult to find the 
actual couple at ¢=0 as the rate of change is then so great. 
Even at the time of the first reading the rate of change was 
very large, so that it was difficult to keep the spot of light 
_ on the scale stationar y. This would tend to make the read- 
ing rather less than the actual couple at the time (as in the 
wase of the first reading on the second day). 
“As far as the observations themselves go the equation 
appears to very fairly represent the curve, the variation 
being at no point more than 3 per cent. 
2. Rate of Decrease of Stress in a Wire kept stretched 
longitudinally at a Constant Length. 
_ An investigation was made of the rate at which the stress 
falls off in a wire kept stretched at a constant length. The 
Fig. 3. 
5 
N 
: 
S 
Wy 
. N | 
. S cone mee 
RE Q Ne fs 
ss ‘ S 
r9 N CQ 
Sa Se 
OY aN 
a ses 
7 
em ELAS 
OPTICAL LEVER fon tarcer SCALE) 
small rate of change of the length necessitated some means of 
magnifying it. A lead wire 240 cms. in length and 1 mm. 
