William Robert Grove - On The Correlation of Physical Forces

In 1846, Grove published On The Correlation of Physical Forces in which he anticipated the general theory of the conservation of energy that was more famously put forward in Hermann von Helmholtz' Über die Erhaltung der Kraft (On the Conservation of Force) published the following year. His 1846 Bakerian lecture relied heavily on his theory.

James Prescott Joule had been inspired to his investigations into the mechanical equivalent of heat by comparing the mass of coal consumed in a steam engine with the mass of zinc consumed in a Grove battery in performing a common quantity of mechanical work. Grove was certainly familiar with William Thomson's theoretical analysis of Joule's experimental results and Thomson's immature suggestions of conservation of energy. Thomson's public champion, Peter Guthrie Tait was initially a supporter of Grove's ideas but later dismissed them with some coolness.

Though Groves's ideas were forerunners of the theory of the conservation of energy, they were qualitative, unlike the quantitative investigations of Joule or Julius Robert von Mayer. His ideas also shaded into broader speculation, such as the nature of Olbers's paradox, which he may have discovered for himself rather than through a direct knowledge.

... it is difficult to understand why we get so little light at night from the stellar universe, without assuming that some light is lost in its progress through space – not lost absolutely, for that would be an annihilation of force – but converted into some other mode of motion.

— On the Correlation of Physical Forces (1874)

Grove also speculated that other forms of energy were yet to be discovered "as far certain as certain can be of any future event."

The probability is that, if not all, the greater number of physical phenomena are, in one sense correlative, and that, without a duality of conception, the mind cannot form an idea of them: thus motion cannot be perceived or probably imagined without parallax or relative change of position ... in all physical phenomena, the effects produced by motion are all in proportion to the relative motion. ... The question of whether there can be absolute motion, or indeed any absolute isolated force, is purely the metaphysical question of idealism or realism.

— On the Correlation of Physical Forces (1874)