In 1848 German physician (no, not a typo) Julius Robert Mayer calculated that if the Sun shone by literally burning a fuel, such as coal, it would use up all its energy within a few thousand years. This was, of course, in the days before special relativity, thermonuclear fusion, or even the chemical composition of the Sun was known. Similarly, he showed that if it was just radiating stored energy, like a hot rock cooling, the Sun would shine for only about 5000 years. As an alternative, he proposed that the Sun was heated by impacts from space debris. Realizing that this would increase the mass of the Sun and hence change orbital parameters of the planets (contrary to observations), he suggested that sunlight was accompanied by the expulsion of the same amount of mass that fell onto it.

In the 1850s, Scottish engineer John Waterston and German physician (again,...

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