On the Georgium Sidus.

London, The Royal Society, 1783. 4to (26.0 x 20.4 cm). 14 pp. Later, period style, marbled wrappers. = The discovery of Uranus by the great British astronomer William Herschel (1738-1822). Herschel first observed the new celestial body in March 1781, and in this paper he concludes that it is, indeed, a "primary planet", which he named after the British monarch King George III (first chapter of this work). The second chapter is titled 'On the diameter and magnitude of the Georgium Sidus : with a description of the dark and lucid disk and periphery micrometers'. Here, he also recorded that on "Oct. 12, 1782. The night was so fine, that I saw the Georgium Sidus very plainly with my naked eye" (p. 11). Finally, Herschel stated that based on calculations made by the French astronomer Joseph Jérôme Lefrançois de Lalande (1732-1807) (communicated in a letter to Herschel), the new planet's distance to the sun was 18,913 times that of the Earth, while the diameter was 4,454 times that of Earth. Extract from the Society's Philosophical Transactions Volume 73. A very good, clean copy with ample margins. PMM 227.