  It has been shown recently that the classical law of elasticity, expressed in
terms of the displacement three-vector and of the symmetric deformation
three-tensor, can be extended to the four dimensions of special and of general
relativity with a physically meaningful outcome. In fact, the resulting stress-
momentum-energy tensor can provide a unified account of both the elastic and
the inertial properties of uncharged matter. The extension of the displacement
vector to the four dimensions of spacetime allows a further possibility. If the
real displacement four-vector is complemented with an imaginary part, the
resulting complex ``displacement'' four-vector allows for a complex, Hermitian
generalisation of the four-dimensional Hooke's law. Let the complex, Hermitian
``stress-momentum-energy'' tensor density built in this way be subjected to the
usual conservation condition. It turns out that, while the real part of the
latter equation is able to account for the motion of electrically charged,
elastic matter, the imaginary part of the same equation can describe the
evolution of the electromagnetic field and of its sources. The Hermitian
extension of Hooke's law is performed by availing of the postulate of
``transposition invariance'', introduced in 1945 by A. Einstein for finding the
nonsymmetric generalisation of his theory of gravitation of 1915.
