  Almost half a century before Einstein expounded his general theory of
relativity, the English mathematician William Kingdon Clifford argued that
space might not be Euclidean and proposed that matter is nothing but a small
distortion in that spatial curvature. He further proposed that matter in motion
is not more than the simple variation in space of this distortion. In this
work, we conjecture that Clifford went further than his aforementioned
proposals, as he tried to show that matter effectively curves space. For this
purpose he made an unsuccessful observation on the change of the plane of
polarization of the skylight during the solar eclipse of December 22, 1870 in
Sicily.
