  The history of structural optimization as an exact science begins possibly
with the celebrated Lagrange problem: to find a curve which by its revolution
about an axis in its plane determines the rod of greatest efficiency. The
Lagrange hypothesis, that the optimal rod possesses the constant cross-section
was abandoned for Euler buckling problem. In this Article the Lagrange
hypothesis is proved to be valid for Greenhill's problem of torque buckling.
The corresponding isoperimetric inequality is affirmed.
