264 HISTORY OF PHYSICAL ASTRONOMY. 



rejected it ; and Fontenelle had congratulated him- 

 self publicly on having narrowly escaped this seduc- 

 tive error. The objections to the admission of the 

 truth arose principally from the inaccuracy of 

 observation, and from the persuasion that the mo- 

 tions of the satellites were circular and uniform. 

 Their irregularities disguised the fact in question. 

 As these irregularities became clearly known, 

 Romer's discovery was finally established, and 

 the "Equation of Light" took its place in the 

 Tables. 



Sect. 3. Discovery of Aberration. Bradley. 



IMPROVEMENTS in instruments, and in the art of 

 observing, were requisite for making the next great 

 step in tracing the effect of the laws of light. It 

 appears clear, on consideration, that since light 

 and the spectator on the earth are both in motion, 

 the apparent direction of an object will be deter- 

 mined by the composition of these motions. But 

 yet the effect of this composition of motions was 

 (as is usual in such cases) traced as a fact in obser- 

 vation, before it was clearly seen as a consequence 

 of reasoning. This fact, the Aberration of Light, 

 the greatest astronomical discovery of the eigh- 

 teenth century, belongs to Bradley, who was then 

 Professor of Astronomy at Oxford, and afterwards 

 Astronomer Royal at Greenwich. Molyneux and 

 Bradley, in 1725, began a series of observations 



