the river Thames, he remarked that every time the boat put about, the vane at the top of the boat's mast shifted a little, as if the wind had slightly changed its direction. Upon expressing to the sailors his surprise at the regular change in the wind, they assured him that it was only apparent, and was owing to the change in the direction of the boat. From that moment he conjectured that all the phenomena which he observed, arose from the progressive motion of light, combined with the earth's motion in its orbit.

In order to convey some idea of this curious discovery, let us suppose a shower of hail to fall perpendicularly on a calm day, and from a small height in the atmosphere, so that the hailstones may descend with very little velocity. If a carriage with its front windows open is standing beneath such a shower, not a single hailstone will enter it. But if the carriage advances in any direction with great velocity, the hailstones will enter the front windows as if they fell obliquely. When a given hailstone has reached the top of the window, the carriage and the window will have advanced a certain distance before the hailstone reaches the bottom of the window; so that it must necessarily fall within it. Now, as this must take place whether the carriage moves north, south, cast, or west, the person within would necessarily conclude that the hailstones did not fall perpendicularly, or from the zenith, but from a point on one side of it; and that this point would describe a small circle round the zenith of the carriage, moved in every possible direction.

Hence it is easy to understand how a star in the zenith must appear at a little distance from the zenith to a spectator who is carried along with the earth in its annual motion.

Roemer, the discoverer of the successive propagation of light, had computed that it moved from the sun to the earth in 11 minutes, while other astronomers had adopted 7 minutes as the most accurate result. Bradley found, from his observations, that if his theory was correct, light should move from the sun to the earth in 8 minutes 12 seconds, a result intermediate between those above mentioned.

It is scarcely necessary to inform the reader, that the happy idea which Bradley had been so fortunate as to seize, furnished him with a complete explanation of all the varied phenomena which he had observed. The discovery of the aberration of the stars, as it was called, established his reputation as the first astronomer of the age, and extended his fame throughout all Europe.

Among the conclusions which Bradley deduced from this discovery, we may mention two of considerable importance in

physics. He inferred, that in the same medium, light was propagated with the same velocity after it had been reflected as before it; and that the light of small as well as of great stars moved with the same velocity.

All those computations,' says Professor Rigaud, speaking of the velocity assigned to light, must of course be founded on the supposi tion of the light reaching us with the same uniform velocity from all the heavenly bodies. Bradley considered this to be established, and so did Clairaut; but if a difference should be clearly ascertained in the maximum of aberration, as derived from the motions of different stars, some modification of this supposition will become necessary. This, however, is a question which requires all the resources of modern astronomy to determine it.'

The important question to which Professor Rigaud here refers, may be considered as determined, within certain limits, by a series of accurate experiments made by M. Fraunhofer and M. Soldner, at Munich. With an instrument of great delicacy, which required to be used simultaneously by two observers looking through different telescopes, they determined that the refractions of the light of different fixed stars did not differ from one another, nor from that of the planets. A difference, amounting to the th part of the whole refractions, could be distinctly perceived with this instrument; and this difference would not amount to the fourth part of a second in the horizontal refraction of the atmosphere. Fraunhofer intended to continue these observations with still nicer instruments; but a premature death has deprived science of his invaluable aid.

In the year 1729, Bradley undertook to deliver the Lectures on Experimental Philosophy at Oxford, a duty which he continued to discharge till April 1760. In 1731 he was an unsuccessful candidate for the office of Keeper of the Ashmolean Museum ; and in 1732 he quitted Wansted, and took up his residence at Oxford.

During the next ten years of our author's life, he does not seem to have been much occupied with his favourite science; and Professor Rigaud has not been able to collect much information respecting his labours in this period. He communicated to the Royal Society in 1734, a paper on the vibrations of the pendulum in different latitudes, and on the figure of the earth which might be deduced from them; and in the year 1738 he transmitted to the same learned body his observations on the comet of 1737.

Bradley was now destined to reach the highest object of his ambition. After the death of Halley in 1742, he was, through the influence of George, Earl of Macclesfield, appointed Astro

nomer-Royal of England. Upon his arrival at Greenwich, in June, he found the instruments in the Observatory in the most wretched condition, and his first cares were devoted to their repair and improvement. With an assistant, carefully trained by himself, he began his labours with a zeal and ardour which it is difficult to estimate. No fewer than 18,000 observations were made in the year 1743 by Bradley and his nephew. He made also a series of experiments on the length of the pendulum, between 1743 and 1749; and he observed with great care the comets of 1743, 1744, and 1748.

In his observations on the aberration of the stars, Bradley remarked that the stars near the equinoctial colure, changed their declination about two seconds more in a year, than they would do if the precession of the equinoxes was only fifty seconds; while those near the solstitial colure changed their declination less than they ought, if its precession were exactly that quantity. Satisfied of the accuracy of his instrument, he continued to observe these stars with the utmost care, with the view of discovering the cause of this apparent anomaly; and having completed his series of observations throughout a complete revolution of the moon's node, he succeeded, in 1747, in establishing his second great discovery of the nutation of the earth's axis. A motion in the earth's axis had been anticipated from theoretical considerations; but Bradley had the sole merit, not only of determining it by accurate observations, but of ascertaining that it arises from the action of the moon upon the equatorial parts of the earth. The radius of the small circle which the earth's axis thus describes during a revolution of the lunar node, was proved by Bradley to be 9 seconds; and Dr Brinkley, Bishop of Cloyne, from a great number of the finest observations, has, in our own day, proved it to be 9 seconds.

This remarkable discovery was communicated to the Royal Society of London, in a letter to George, Earl of Macclesfield, dated December 31st, 1747; and we owe it to the memory of that distinguished Astronomer and patron of science, to insert the introductory paragraphs of Dr Bradley's letter, which we can assure our readers are not written in the language of adulation.

'The advantages arising from different persons attempting to settle the same points of astronomy near the same time are so much the greater, as a concurrence in the result would remove all suspicion of incorrectness in the instruments made use of. For which reason I esteem the curious apparatus at Shirburn Castle (the seat of the Earl of Macclesfield), and the observations there taken, as a most valuable criterion, whereby I may judge of the accuracy of those that are made at the Royal Observatory; and, as a lover of science, I cannot but wish that

our nation abounded with more frequent examples of persons of like rank and ability with your Lordship, equally desirous of promoting this, as well as every other branch of natural knowledge, that tends to the honour and benefit of our country.

But were the patrons of arts and sciences ever so numerous, the subject of my present letter is of such a nature, as must direct me to beg leave to address it to the Earl of Macclesfield; not only as a most competent judge of it, but as the sole person in this nation, that hath instruments proper to examine into the truths of the facts here related. And it is a particular satisfaction to me, that after so long an attendance upon these phenomena, I am allowed the honour of transmitting the account of them to the public through your Lordship's hands, as it gives me at the same time an opportunity of professing the grateful sense I shall ever retain, both of the signal favours which I formerly received from the noble Lord your father, and of the many recent obligations conferred by yourself.'

This letter was received by the Royal Society with peculiar favour. On the 14th December, 1730, when Bradley communicated to that body his discovery of the Aberration, it was unanimously resolved by the council to discharge him from future payments, ' and to give him liberty to take up his bond gratis, in considera'tion of his useful and curious discoveries and inventions in As، tronomy, which redounded greatly to the honour of the Society ;' but as Bradley was now above the world, the council voted to him the Copley medal for his paper on Nutation, and in the vote of thanks which they recorded, they characterised his discoveries as a lasting honour to himself, to his country, and to the pre'sent age.'

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In the year 1726, an attempt was made by the Royal Society to obtain a small sum from Government to provide suitable instruments for the Royal Observatory; but the ignorant administrations which governed England at that period, spurned from them the claims of science. A petition of the same body in 1748, received more attention ; and upon the recommendation of Lord Anson and the Lords of the Admiralty, L.1000 was given by the King,' to be paid out of the money arising from the old ' stores of the navy, to buy some astronomical instruments for 'the use of the Royal Observatory.' This miserable donation, so miserably given, after twenty-four years of supplication, was laid out by Bradley with great judgment and economy; and with the assistance probably of the Board of Ordnance, the Observatory was put into a respectable state of repair.

Dr Bradley seems to have had a considerable share in the assimilation of the British Kalendar to that of other nations. Lord Chesterfield was the original promoter of this measure, which was supported by the Earl of Macclesfield, Lord Chancellor Hard

wick, and Mr Pelham, and finally carried in 1751. Bradley composed the three tables at the end of the bill, the first of which is found in the English Prayer-Book; and Lord Macclesfield had the charge of the provisions of the bill, and supplied all the science which it required. The following curious anecdote happily illustrates the presumption and ignorance of the mob of those days:

'Lord Chesterfield took pains, in the periodical journals of the day, to prepare the minds of the public for the change; but he found it much easier to prevail with the legislature, than to reconcile the great mass of the people to the abandonment of their inveterate habits. When Lord Macclesfield's eldest son stood the great contested election for Oxfordshire in 1754, one of the most vehement cries raised by the mob against him, was, "Give us back the eleven days we have been robbed of" and even several years after, when Bradley, worn down by his labours in the cause of science, was sinking under the disease which closed his mortal career, many of the common people attributed his sufferings to a judgment from heaven, for his having been instrumental in what they considered to be so impious an undertaking.'

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When Bradley accepted of the office of Astronomer-Royal in 1742, he became entitled,' as Professor Rigaud states, to no 'more than the L.100 per annum which had been originally assigned to Flamstead, and which was considerably reduced by the fees deducted from it at the public offices. For nearly ten years he received only this miserable pittance; and though Mr Pelham offered him, in 1751, the Vicarage of Greenwich, yet he felt the incompatibility between the duties of an AstronomerRoyal and those of an officiating clergyman, and from the noblest motives he refused to accept of it. This generous and highminded sacrifice met with an immediate reward. On the 15th February, 1752, the King granted him a pension of L.250 per annum, in consideration of his great skill and knowledge in the 'several branches of astronomy and the other parts of mathematics, which have proved so useful to the trade and navigation of the kingdom.'

With this new incentive to labour, Bradley continued his observations with unremitting ardour; and the reader may form some idea of his diligence from the fact, that the Greenwich observations between 1750 and 1762, which have been published, occupy 931 large folio pages, and contain about 60,000 observations.

Fatigued by his numerous duties, Bradley resigned in 1760 his office of Reader on Experimental Philosophy at Oxford; and the last scientific object to which he was able to attend, was the transit of Venus in 1761. The Royal Society had proposed to

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