262 HISTORY OF PHYSICAL ASTRONOMY. 



Refractions, which was published under Halley's 

 name in the Philosophical Transactions for 1721, 

 without any indication of the method by which it 

 was constructed. But M. Biot has recently shown 3 , 

 by means of the published correspondence of Flam- 

 steed, that Newton had solved the problem in a 

 manner nearly corresponding to the most improved 

 methods of modern analysis. 



D. Cassini and Picard proved*, Le Monnier in 

 1738 confirmed more fully, the fact that the varia- 

 tions of the Thermometer affect the Refraction. 

 Mayer, taking into account both these changes, and 

 the changes indicated by the Barometer, formed a 

 theory, which Lacaille, with immense labour, ap- 

 plied to the construction of a Table of Refractions 

 from observation. But Bradley's Table (published in 

 1763 by Maskelyne,) was more commonly adopted 

 in England ; and his formula, originally obtained 

 empirically, has been shown by Young to result 

 from the most probable suppositions we can make 

 respecting the atmosphere. Bessel's Refraction 

 Tables are now considered the best of those which 

 have appeared. 



Sect 2. Discovery of the Velocity of Light 

 Romer. 



THE astronomical history of Refraction is not 

 marked by any great discoveries, and was, for the 



3 Biot, Acad. Sc. Comple Rendtt. Sept. 5, 1836. 



4 Bailly, iii. 92. 



