DELISLE, JOSEPH NICOLAS French as tronomer, was born in Paris on April 4, 1688. He proposed in 1715 the "Diffraction-theory" of the sun's corona, visited England and was received into the Royal Society in 1724, and left Paris for St. Petersburg on a summons from the empress Catherine towaids the end of 1725. Having founded an observatory there, he re turned to Paris in 1747, was appointed geographical astronomer to the naval department, and installed an observatory in the Hotel Cluny. Charles Messier and J. J. Lalande were among his pupils. He died of apoplexy at Paris on Sept. 12, 1768.
Delisle is chiefly remembered as the author of a method for observing the transits of Venus and Mercury by instants of con tacts which was first proposed by him in a letter to J. Cassini in 1743. In his Memoires pour servir a l'histoire et an progres de l'astronomie (St. Petersburg, 1738), he gave the first method for determining the heliocentric co-ordinates of sun-spots.
See S. Newcomb, Washington Observations for 1875, app. ii. pp. 176-189.