SUCCESSORS OF NEWTON IN ASTRONOMY 



solution of this mystery that puzzled Halley and his 

 associates all their lives was finally attained. 



BRADLEY AND THE ABERRATION OF LIGHT 



Halley was succeeded as astronomer royal by a man 

 whose useful additions to the science were not to 

 be recognized or appreciated fully until brought to 

 light by the Prussian astronomer Bessel early in the 

 nineteenth century. This was Dr. James Bradley, an 

 ecclesiastic, who ranks as one of the most eminent 

 astronomers of the eighteenth century. His most re- 

 markable discovery was the explanation of a peculiar 

 m lion of the pole-star, first observed, but not explain- 

 ed, by Picard a century before. For many years a 

 satisfactory explanation was sought unsuccessfully by 

 Bradley and his fellow-astronomers, but at last he was 

 able to demonstrate that the star 7 Draconis, on which 

 he was making his observations, described, or appeared 

 to describe, a small ellipse. If this observation was 

 correct, it afforded a means of computing the aberration 

 of any star at all times. The explanation of the 

 physical cause of this aberration, as Bradley thought, 

 and afterwards demonstrated, was the result of the 

 combination of the motion of light with the annual 

 motion of the earth. Bradley first formulated this 

 theory in 1728, but it was not until 1 748 twenty years 

 ntinuous struggle and observation by him that he 

 was prepared to communicate the results of his efforts 

 to the Royal Society. This remarkable paper is 

 thought by the Frenchman, Delambre, to entitle its 

 author to a place in science beside such astronomers as 

 Ilipparchus and Kepler. 



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