Photo courtesy Observatoire de Paris
Henri Alexandre Deslandres
24 July 1853	1921 Bruce Medalist	15 January 1948

After graduating from l’École Polytechnique, Henri Deslandres spent seven years in the army before resigning to resume his studies at l’École Polytechnique and the Sorbonne. He worked at the Paris and Meudon Observatories, directing the latter from 1908 until their merger in 1926 and then both until 1929, with time out for military service during World War I. He made significant contributions to the investigation of molecular spectra, finding empirical laws that became more useful after the development of quantum mechanics. He observed spectra and measured radial velocities of planets and stars. He determined the rotation rates of Uranus, Jupiter and Saturn and the Saturnian rings (shortly after James E. Keeler). He invented the spectroheliograph at about the same time as George E. Hale, and he made extensive studies of the solar chromosphere and solar activity. He named plages and filaments, and he showed that the latter are the same structures as prominences. Convinced that sunspots were magnetic phenomena, he began a long-term program of photographing the sun daily.

Presentation of Bruce medal
Moore, J.H., PASP 33, 71-78 (1921).

Some offices held
Académie des Science, President, 1920.

Other awards
National Academy of Sciences, Henry Draper Medal, 1913.
Royal Astronomical Society, Gold medal, 1913, presented by F.W. Dyson, MNRAS 73, 317-29 (1913).

Biographical materials
Bigg, Charlotte, Biographical Encyclopedia of Astronomers (Springer, NY, 2007), pp. 294-95.
Michard, R., Dictionary of Scientific Biography 4, 68-70.
Tenn, Joseph S., “Henri Deslandres: The Sixteenth Bruce Medalist,” Mercury 22, 1, 18 (1993).

Obituaries
d’Azambuja, L., Bulletin de la Société astronomique de France 62, 179-84 (1948).
Danjon, M.A., Bulletin de la Société astronomique de France 62, 79-80 (1948).
Lyot, B., Notices et Discours, Acad. Sci., Paris 2, 682-687 (1949).
Nature 161, 303 (1948).
Stratton, F.J.M., Obituary Notices of the Fellows of the Royal Society of London 9, 65-77 (1954).
Stratton, F.J.M., MNRAS 109, 141-44 (1949).
More obituaries

Portraits
Bulletin de la société astronomique de France, 1913 [photograph, via Wikimedia]
Getty Images, 1910 aboard ship
Johns Hopkins University, with his student, Lucien d’Azambuja

Named after him
Lunar crater Deslandres
Minor Planet #11763 Deslandres
Deslandres Prize of the French Academy of Science

More references