Sect, VIII.] yfstrono7?ii/. 71 



number of important discoveries, and useful pub- 

 lications. Among many others which might be 

 mentioned, he discovered the Accekration of the 

 Moon, and gave a very ingenious method of find- 

 ing her parallax. He composed tables of the Sun, 

 the Moon, and all the planets. He also recom- 

 mended the mode of ascertaining the Longitude 

 by Lunar Observations ; a mode which has been 

 since much improved, and generally adopted ^ and 

 which is, at present, the most certain guide of the 

 mariner. After him, at the head of the Royal Ob- 

 servatory was placed Dr. Bradley, who greatly 

 distinguished himself as a practical astronomer. 

 He was the first who made observations with suffi- 

 cient accuracy to detect the smaller inequalities 

 in the motions of the planets and fixed stars. By 

 means of this accuracy, he discovered, in 1727} the 

 aberration of the stars^ a phenomenon produced by 

 the compound motion of the earth, and the ra} s of 

 light ; and furnishing new proof, both of the mate- 

 riality and amazing velocity of light, and also of 

 the reality of that motion which had been ascribed 

 to the earth. The same gentleman, in 17^7? dis- 

 covered the nutation of the earth's axis — that libra- 

 tory motion, which is occasioned by the inclina- 

 tion of the moon's orbit to the ecliptic, and the re- 

 trograde revolution of her nodes ; thus, in the 

 course of ten years, making two of the most im- 

 portant additions to astronomical knowledge that 

 \X\e century produced*. 



* The Rev. James Bratlley was born in the year l6()2, and 

 educated at Oxford. On the death of Dr. Halley he was ap- 

 pointed Astronomer Roynl, in which office he continued till his 

 death, which took place in 17<)2. 



