In thermodynamics, the conservation of force or "law of conservation of force" is a view, promoted largely by German physicist Hermann Helmholtz, beginning in 1847, which argues that the quantity of force in the universe, called “kraft”, is conserved. [1] The logic of the theory was later re-incorporated into the more robust law of conservation of energy and then into the first law of thermodynamics, by German physicist Rudolf Clausius. The law of conservation of force, according to Helmholtz, states:

“The quantity of force which can be brought into action in the whole of nature is unchangeable, and can neither be increased nor diminished.”

The theory of the conservation of force has a long and elaborate history. According to Helmholtz, the primary curator of this principle, the "law of conservation of force", as he called, had been enunciated prior to him by Isaac Newton, Daniel Bernoulli, Benjamin Thomson, and Humphry Davy. [2] Likewise, in the 1670s the theory of vis viva or “living force” of German mathematician Gottfried Leibniz was prominant. In 1837, German pharmacist Karl Mohr gave one of the earliest statements of the conservation of force or Kraft: [3]

“Besides the fifty-four known chemical elements there is in the physical world one agent only, and this is called Kraft. It may appear, according to circumstances, as motion, chemical affinity, cohesion, electricity, light and magnetism; and from any one of these forms it can be transformed into any of the others.”

In the years to follow, building on Helmholtz, others began to profess their views on the conservation of force, such as English chemist Michael Faraday who later developed the theory of "lines of force" (field lines), a theory very influential to Scottish physicist James Maxwell. [4]

1. Helmholtz, Hermann. (1947). "The Conservation of Force: A Physical Memoir." In Selected Writings of Hermann von Helmholtz (1971), ed. R. Kahl, pgs. 3-55. Middletown, CT: Wesleyan University Press.
2. Helmholtz, Hermann. (1862). “On the Conservation of Force: Introduction to a Series of Lectures Delivered at Carlsruhe in the Winter of 1862-63” [URL]. In Scientific Papers: the Harvard Classics. Translated by Edmund Atkinson.
3. Mohr, K. F. (1837) "Ansichten über die Natur der Wärme" (“Views on the Nature of Heat”). Ann. der Pharm., 24, pp. 141–147.
4. Grove, William R., Faraday, Michael, Liebig, Justus, and Carpenter, William. (1876). The Correlation and Conservation of Forces. D. Appleton and Co.

Further reading
● Faraday, Michael. (1857). “On the Conservation of Force”, Philosophical Magazine. Vol. 13, pg. 227-34.
● Faraday, Michael. (1859). “On Regelation, and the Conservation of Force, Philosophical Magazine, Vol. 17. Pgs 166-69.

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