vin 



the Precession of the Equinoxes, Theory of the Motion of the Moon, ele- 

 mentary treatises on Astronomy and Mechanics, and many miscellaneous 

 papers in the ' Comptes Eendus,' ' Connaissance des Temps,' and in the 

 Journal of the Ecole Polytechnique. He was also the author of some 

 excellent elementary books on astronomy and mechanics. Soon, however, 

 his attention became engaged by astronomical questions, and before long 

 he was entirely absorbed by them. He published an important treatise 

 on the Theory of the Tides, and about the same time the question of the 

 Lunar Theory began to occupy him. 



His greatest work, ' La Theorie de la Lune ' (the first part of which 

 occupied him fourteen years), was published in 1860 as an entire volume 

 of ' Memoires ' of the Academie des Sciences. It made his name famous 

 among astronomers. In 1862 the Royal Astronomical Society of London 

 elected him one of their Associates ; and in February 1870 Professor J. 

 C. Adams presented to him, in the name of the President, the Gold Medal 

 of the Society, in acknowledgment of the high opinion of his work enter- 

 tained by English astronomers. 



During the same time he published a number of papers relating to the 

 theory, one in particular on the secular acceleration of the mean motion 

 of the moon, which was then a subject of much controversy. 



The second volume of his ' Theorie ' appeared in 1867. The prepara- 

 tion of the Lunar Tables necessary for the completion of the work was 

 undertaken by the Bureau des Longitudes, under the direction of 

 Delaunay. A government grant of funds was obtained for the pur- 

 pose, and the tables were in course of preparation at the time of his 

 death. It was uncertain whether the calculations were sufficiently 

 advanced to be carried on without him ; but M. Puiseau, Member of 

 the Bureau des Longitudes, says, " Quoique l'auteur ne soit plus la pour 

 y mettre la derniere main, il ne sera sans doute pas impossible de terminer 

 ce monument scientifique. Esperons pour la gloire de Tastronomie 

 frangaise que ce service sera rendu a la science, que ce supreme hommage 

 ne manquera pas a notre illustre confrere." 



In the year 1854, when the administration of the observatory of Paris 

 was separated from that of the Bureau des Longitudes, several of the 

 members of its staff retired to a house in the Rue Notre Dame des 

 Champs, where they established a small observatory. Delaunay occu- 

 pied an apartment in the same house, and there he formed a life-long 

 friendship with Mathieu and Laugier. It was there that he worked out 

 most of his researches, seldom going out except to give his lessons at 

 the Ecole des Mines or the Sorbonne. He often began work as early 

 as five in the morning, and invariably continued until late in the evening. 

 Prom this tranquil life he was called away in 1870 by the Emperor 

 Napoleon the Third to succeed M. Leverrier as Director of the Paris 

 Observatory. Many alterations and improvements had taken place in 

 the Observatory since the death of Arago, and Delaunay soon became 



