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Although ancient philosophers as far back as Thales of Miletus may have had inklings of the First Law, it was first stated in its modern form by the German surgeon Julius Robert von Mayer ( 1814- 1878) in his "Remarks On the Forces of Inorganic Nature" in Annalen der Chemie und Pharmacie, 43, 233 (1842). Mayer reached his conclusion on a voyage to the Dutch East Indies (now Indonesia), where he found that his patients' blood was a deeper red, because they were consuming less oxygen, and therefore less energy, to maintain their body temperature in the hotter climate. He had discovered that heat and work were both forms of energy, and later, after improving his knowledge of physics, he calculated a quantitative relationship between them.

Meanwhile, in 1843 James Prescott Joule independently discovered the law by an experiment, now called the "Joule apparatus", in which a descending weight attached to a string caused a paddle immersed in water to rotate. He showed that the gravitational potential energyPotential energy U or E , a kind of scalar potential, is energy by virtue of matter being able to move to a lower-energy state, releasing energy in some form. For example a mass released above the Earth has energy resulting from the gravitational attracti lost by the weight in descending was equal to the thermal energy ( heat) gained by the water by frictionIn physics, friction is the resistive force that occurs when two surfaces travel along each other when forced together. It causes physical deformation and heat buildup. The frictional force is a function of the force pressing the surfaces together and the with the paddle.

Unfortunately for Mayer, his work was overlooked in favour of Joule's, and Mayer attempted to commit suicide. Later, Mayer's reputation was restored by a sympathetic account in John TyndallThis article is about the 19th century scientist. For the 20th century British politician of the same name, see John Tyndall (politician). John Tyndall ( August 2, 1820 December 4, 1893), Irish natural philosopher, was born in Co. Carlow, Ireland, his fat's Heat: A Mode of Motion (1863).

A similar law was written in the privately published Die Erhaltung der Kraft ( 1847Events January 4 Samuel Colt sells his first revolver pistol to the United States government. January 13 The Treaty of Cahuenga ends the Mexican-American War in California. January 16 John C. Fremont is appointed Governor of the new California Territory.) by Hermann von HelmholtzHermann Ludwig Ferdinand von Helmholtz ( August 31, 1821 September 8, 1894) was a German physician and physicist. Helmholtz was the son of a gymnasium headmaster, Ferdinand Helmholtz, who had studied classical philology and philosophy, and who was a close.

With the discovery of special relativitySpecial relativity (SR or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. It replaced Newtonian notions of space and time, and incorporated electromagnetism as represented by Maxwell's equations. The theory is by Albert EinsteinAlbert Einstein ( March 14 1879 April 18 1955) was a theoretical physicist who is widely regarded as the greatest scientist of the 20th century. He proposed the theory of relativity and also made major contributions to the development of quantum mechanics, conservation of energy was shown to be a special case of a more general rule. According to special relativity, mass and energy are interchangeable in the famous equation E = mc².

Conservation of energy can be shown through Noether's theorem to be the result of the time-invariance of the laws of physics.

Within the realm of quantum mechanics, conservation of energy is violated for extremely small time scales due to the uncertainty principle.