208 
IOWA ACADEMY OP SCIENCE 
Vol. XXIV, 1917 
over this amplitude was 7.6 per cent. The case illustrated shows 
the greatest deviation in period of all the wires. The range in 
this variation among all the wires experimented with was from 
0.5 to 7.6 per cent. 
Coefficient of Simple Rigidity . — There are at least two ways 
of determining the rigidity of such wires; by a kinetic, and by 
a static method. In the former if one knows the length and 
radius of the wire, the moment of inertia of the suspended system, 
and its period of vibration, he can readily calculate n, the co- 
efficient of simple rigidity, by a well known formula. The dif- 
o 
ficulty arises here that one is at a loss what period of vibration to 
choose. Since in the experiment with the wire illustrated in 
figure 28, the period varied by 7.6 per cent, and since the value 
of n depends upon the square of the period, it is seen that the 
range in the value for n will be approximately 15 per cent. 
There is no good reason for using any one of the values of the 
period over any other one, but in order to be consistent the 
smallest values were uniformly used. 
In the static method the torsional couple exerted by the wire 
was balanced by the bending of two glass fibers, which had pre- 
viously been calibrated. The values of n determined statically 
