ÅNGSTRÖM, (ANDERS JONAS). - HALLEY'S COMET.

Sur deux Inégalités d'une grandeur remarquable dans les Apparitions de la Comete de Halley.

Uppsala, C.A. Leffler, 1862. 4to. Later blank boards. Uncut. Offprint from "Nova Acta Reg.Soc. Sc. Ups.". 10 pp. and 1 folded plate.

First edition. In this paper Ångström deduces the mean period of Halley's Comet by a statistical approach. From his analysis he discovered that the average time between perihelions was 76.93 years and found that thsi period varied in a cyclical manner.

Ångström was one of the early formulators of the science of modern spectroscopy; he wrote extensively on terrestrial magnetism, the conduction of heat, and especially spectroscopy. He published a monumental map of the normal solar spectrum that expressed the length of light waves in units of one ten-millionth of a millimeter, a unit of length now known as the angstrom. He discovered that hydrogen is present in the sun's atmosphere, and he was the first to examine the spectrum of the aurora borealis.

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