A further great scientific discovery, this time in physics, was the Mayer-Joule demonstration of the transformation of heat into mechanical energy and of mechanical energy into heat.
(A further great scientific discovery; was; the Mayer-Joule demonstration of the transformation of heat into mechanical energy and of mechanical energy into heat)
A further great scientific discovery
was
the Mayer-Joule demonstration of the transformation of heat into mechanical energy and of mechanical energy into heat