towards a star so as to place it apparently in the centre of the field of view, yet it was not generally the true position of the star.  It was not, in fact, the position in which the star would have been observed had the earth been at rest.  Provided with this suggestion, he explained the apparent movements of the stars by the principle known as the “aberration of light.”  Every circumstance was accounted for as a consequence of the relative movements of the earth and of the light from the star.  This beautiful discovery not only established in the most forcible manner the nature of the movement of light; not only did it illustrate the truth of the Copernican theory which asserted that the earth revolved around the sun, but it was also of the utmost importance in the improvement of practical astronomy.  Every observer now knows that, generally speaking, the position which the star appears to have is not exactly the position in which the star does actually lie.  The observer is, however, able, by the application of the principles which Bradley so clearly laid down, to apply to an observation the correction which is necessary to obtain from it the true place in which the object is actually situated.  This memorable achievement at once conferred on Bradley the highest astronomical fame.  He tested his discovery in every way, but only to confirm its truth in the most complete manner.

Halley, the Astronomer Royal, died on the 14th, January, 1742, and Bradley was immediately pointed out as his successor.  He was accordingly appointed Astronomer Royal in February, 1742.  On first taking up his abode at Greenwich he was unable to conduct his observations owing to the wretched condition in which he found the instruments.  He devoted himself, however, assiduously to their repair, and his first transit observation is recorded on the 25th July, 1742.  He worked with such energy that on one day it appears that 255 transit observations were taken by himself alone, and in September, 1747, he had completed the series of observations which established his second great discovery, the nutation of the earth’s axis.  The way in which he was led to the detection of the nutation is strikingly illustrative of the extreme care with which Bradley conducted his observations.  He found that in the course of a twelvemonth, when the star had completed the movement which was due to aberration, it did not return exactly to the same position which it had previously occupied.  At first he thought this must be due to some instrumental error, but after closer examination and repeated study of the effect as manifested by many different stars, he came to the conclusion that its origin must be sought in some quite different source.  The fact is that a certain change takes place in the apparent position of the stars which is not due to the movement of the star itself, but is rather to be attributed to changes in the points from which the star’s positions are measured.