Authorities and Books for Students 415 



Bradley (edited by Rigaud), from which the portrait has been 

 taken. My account of Halley's work is based to a considerable 

 extent on his own writings ; there is a good deal of biographical 

 information about him in the books already quoted in connection 

 with Newton and Flamsteed, and there is a useful article on 

 him in the Dictionary of National Biography. I have made 

 a good deal of use in this chapter of Wolf and Delambre, 

 especially in dealing with Continental astronomers ; and for 

 special parts of the subject I have used Grant's History if 

 Physical Astronomy, Todhunter's History of the Mathematical 

 Theories of Attraction and the Figure of the Earth, and 

 Poynting's Density of the Earth. 



Chapter XL Most of the biographical material has been 

 taken from Wolf, from articles in various encyclopaedias and 

 biographical dictionaries, chiefly French, and from Delambre's 

 hloge of Lagrange. The two portraits are taken respectively 

 from Serret's edition of the Oeuvres de Lagrange and from 

 the Academy's edition of the Oeuvres Completes de Laplace. 

 Gautier's Essai Historique sur le Probleme des Trots Corps and 

 Grant's History of Physical Astronomy have been the books most 

 used for my account of the scientific contributions of the various 

 astronomers dealt with ; I have also consulted various modern 

 treatises on gravitational astronomy, especially Tisserand's 

 Mecanique Celeste, Brown's Lunar Theory, and to a less extent 

 Cheyne's Planetary Theory and Airy's Gravitation. For special 

 points I have used Todhunter's History, already referred to. 

 Of the original writings I have made a good deal of use of 

 Laplace's Mecanique Celeste as well as of his Systeme du Monde ; 

 I have also consulted a certain number of his other writings and 

 of those of Lagrange and Clairaut ; but have made no systematic 

 study of them. 



Students who wish to know more about gravitational astronomy 

 but have little knowledge of mathematics should try to read 

 Airy's Gravitation ; Herschel's Outlines of Astronomy and 

 Grant's History (quoted above) also deal with the subject 

 without employing mathematics, and are tolerably intelligible. 



Chapter XII. The account of Herschel's career is taken 

 chiefly from Mrs. John Herschel's Memoir of Caroline Herschel, 

 from Miss A. M. Clerke's The Herschels and Modern Astronomy, 

 from the Popular History of Astronomy in the Nineteenth 

 Century by the same author, and from Holden's Sir William 

 Herschel, his Life and\ Works. The last three books and the 

 Synopsis and Subject Index to the Writings of Sir William 

 Herschel by Holden & Hastings have been my chief guides to 

 Herschel's long series of papers ; but nearly everything that I 

 have said about his chief pieces of work is based on his own 



