Edmond Halley (1656-1742), appointed Astronomer Royal in 1720, is best known for his work with comets, such as the famous comet of 76 year periodicity which bears his name. He was the first to suggest that nebulae were clouds of interstellar gas within which stars were being formed. Halley had many scientific interests outside astronomy. He produced work in meteorology and geophysics, correctly proposed that the salt in the sea came from river-borne land deposits, and estimated the size of the atom. Halley worked with Newton on his books, 'Principia' and 'Opticks', and became a Fellow of the Royal Society in 1678.
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