Edmund Halley, James Bradley 61 



Bradley went to reside with his uncle, and became interested 

 in astronomical work. His observational skill soon secured 

 results of sufficient importance to justify his election to the 

 fellowship of the Royal Society in 1718, and the appointment 

 to the Savilian Chair of Astronomy in 1721. He, however, 

 continued to live in Wanstead even after the death of his 

 uncle, visiting Oxford only for the delivery of his lectures. 



It was known to Robert Hooke that the distance of the 

 stars might be ascertained by noting their change of position 

 at different times of the year, for as the earth revolves round 

 the sun, we look upon each star from a slightly different 

 point of view according to the position of the earth in its 

 orbit. The more remote the stars, the smaller will be the 

 displacement, and no one could tell beforehand whether 

 any of them were sufficiently near to show a measurable 

 effect. Hooke himself, with his accustomed impetuosity, had 

 tried the method, and using a star which for particular 

 reasons was specially fitted for the purpose, believed that he 

 had observed a comparatively large displacement. Samuel 

 Molyneux (see page 90) had erected a suitable telescope 

 at his house in Kew Green, for the purpose of verifying 

 Hooke's observations, and observed the same star on a 

 series of evenings during the early part of December, 1725, 

 but no material change of position was noted. At this 

 stage Bradley, a friend of Molyneux, began to take part 

 in the investigation. On visiting the Observatory at Kew 

 on December 17th, curiosity tempted him to take an observa- 

 tion, and he noted that the star had slightly increased in 

 declination. To his surprise, however, the displacement was 

 found to be in a direction opposite to that to be expected 

 if it were due to the proximity of the star. The apparent 

 movement was then continuously watched, and the star 

 was found to describe a closed curve, returning at the end of 

 a year's observation very nearly to its original position. 

 Bradley, much puzzled by the result, at first thought that 

 the displacement might be due to a periodic change in the 

 inclination of the earth's axis. In order to test this idea, 

 it was necessary to observe stars in different parts of the 

 sky, and Bradley set up a new instrument at his home in 

 Wanstead for the purpose. He found, indeed, that every 



