Fig. 21.
The derivative of this, with respect to
, gives the intensity,
, at the depth,
, exactly the same as [Equation (1)], and the subsequent deductions hold. Thus the fundamental [Equation (1)], according to the interpretation given, is seen to correspond to a prism of rupture,
, which is a little nearer the true one, having a curved surface of rupture, than the wedge,