Max von Laue,
On the Discussion Concerning Rigid Bodies in the Theory of Relativity
“ Now, in Newton's mechanics there is of course another definition of rigidity, which fits even better to the physical state of facts; there, one considers the rigid body as the limiting case of a deformable body with a very great elasticity coefficient. This passage to the limit can in any case also be executed in the theory of relativity, although it wouldn't lead to the rigid body, but to a body deformable as less as possible, which possibly has especially simple properties as well. ”
