We are still able to identify the very spot on which the telescope stood which was used in this memorable research.  It was erected at the house then occupied by Molyneux, on the western extremity of Kew Green.  The focal length was 24 feet 3 inches, and the eye-glass was 3 and a half feet above the ground floor.  The instrument was first set up on November 26th, 1725.  If there had be any appreciable disturbance in the place of Beta Draconis in consequence of the movement of the earth around the sun, the star must appear to have the smallest latitude when in conjunction with the sun, and the greatest when in opposition.  The star passed the meridian at noon in December, and its position was particularly noticed by Molyneux on the third of that month.  Any perceptible displacement by parallax—­for so the apparent change in position, due to the earth’s motion, is called—­would would have made the star shift towards the north.  Bradley, however, when observing it on the 17th, was surprised to find that the apparent place of the star, so far from shifting towards the north, as they had perhaps hoped it would, was found to lie a little more to the south than when it was observed before.  He took extreme care to be sure that there was no mistake in his observation, and, true astronomer as he was, he scrutinized with the utmost minuteness all the circumstances of the adjustment of his instruments.  Still the star went to the south, and it continued so advancing in the same direction until the following March, by which time it had moved no less than twenty seconds south from the place which it occupied when the first observation was made.  After a brief pause, in which no apparent movement was perceptible, the star by the middle of April appeared to be returning to the north.  Early in June it reached the same distance from the zenith which it had in December.  By September the star was as much as thirty-nine seconds more to the north than it had been in March, then it returned towards the south, regaining in December the same situation which it had occupied twelve months before.

This movement of the star being directly opposite to the movements which would have been the consequence of parallax, seemed to show that even if the star had any parallax its effects upon the apparent place were entirely masked by a much larger motion of a totally different description.  Various attempts were made to account for the phenomenon, but they were not successful.  Bradley accordingly determined to investigate the whole subject in a more thorough manner.  One of his objects was to try whether the same movements which he had observed in one star were in any similar degree possessed by other stars.  For this purpose he set up a new instrument at Wanstead, and there he commenced a most diligent scrutiny of the apparent places of several stars which passed at different distances from the zenith.  He found in the course of this research that other stars exhibited movements of a similar description to those which had already proved so perplexing.  For a long time the cause of these apparent movements seemed a mystery.  At last, however, the explanation of these remarkable phenomena dawned upon him, and his great discovery was made.