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productions on philosophical subjects, are composed with an enviable union of the most complete perspicuity, with all that elegance of style which, without being disfigured by attempts at ornament unsuited to the subject, at once illustrates it, and renders it inviting to the general reader. Like his great predecessor Newton, he evinced most sensibly the humility of true intellectual superiority; and the last sentence he uttered was, "What we know is little, and what we are ignorant of is immense."

Laplace, born in 1749, was at an early age distinguished for his mathematical abilities; and no sooner had he been named professor of mathematics in the military school at Paris, than he began to form that lofty project to which he devoted the entire energies of his genius, and the whole remainder of his life. The great work he planned and executed has been termed the Almegest of the eighteenth century; but, relatively to the age, it is a far more wonderful production than its prototype. The original discoveries of the author embodied in it, are the solutions of the highest problems which the mechanism of the universe presents; many of them had baffled the attempts of all preceding mathematicians, and some received not only their solution, but their first suggestion, from Laplace himself. He was fortunate in enjoying, through a long life, the situation and the means for the uninterrupted prosecution of abstruse research: his residence at Arcueil was the centre of attraction to all the mathematical philosophers of Europe. He died in 1827, when his varied labours had been brought nearly to their complete perfection.

The works of Laplace will be his enduring monument to the world; but to the astronomer, even of the remotest age, there will be a memorial of a loftier, and yet more enduring kind, perpetually exhibited. Those periods in all the irregularities of the planetary motions by which the stability of the system is secured, and which he has so surprisingly established, will be recog

nised in the observations of the most distant epochs, and the memory of Laplace will be cherished in their recurrence. In the lunar motions will be found those changes which will be the fulfilment of his predictions; and the completion of the long periods of the great inequalities of Jupiter and Saturn, will recall his investigations who was the first to examine and explain their laws.

The whole course and manner of his life was regulated with a sole view to the purposes of philosophic investigation. He devoted the energies of his existence to his labours in interpreting the mechanism of the material world; he dedicated to science a life of research; and science, in return, has conferred on him an immortality of fame.

Among the most valuable labours of his successors we may enumerate the publication of the "Theoria Motûs," &c. by Gauss, in 1809; the masterly researches on the attraction of spheroids, in the same and following year, by Mr. Ivory (almost the only British philosopher who, till very lately, attained any high distinction in these researches); the investigation of Gauss, on the same subject, in 1810; and of Bessel, on the perturbations, in 1824. Whilst the researches of Messrs. Lubbock and Ivory, on the same subject, in 1830 to 1832; and those of Professor Airy, on the figure of the earth` and on the solar and planetary theories; and of Encke on the physical theory of his comet; may, perhaps, be considered as some of the most remarkable among the similar investigations of the present day.

Plane Astronomy.

In astronomical observation, the period since the time of Newton has, indeed, been productive of most valuable discoveries. The immense improvement in the construction of astronomical instruments, and in the art of observing, has been naturally followed by a highly increased accuracy of results, and numerous accessions

to our knowledge of the heavenly bodies. And in all these we can, with just pride, observe, that our country has borne its full share.

We have alluded to Halley's labours. He added to them the glory of being the first to predict the return of a comet. Having noticed an agreement in the elements of several which had appeared at successive periods, he concluded them to be reappearances of the same body, obeying the law of an elliptic orbit. He foretold a return in 1758, which was completely verified.

Bradley, associated with Molyneux, commenced, in 1725, that valuable series of observations which led to the discovery of the aberration and the nutation of the earth's axis. The former a consequence of the finite velocity of light, the latter of gravitation.

The measures of the arc of the meridian were now repeated with increased accuracy in France, by La Hire and Cassini, but seemed to lead to the strange and paradoxical result of the earth's figure being a prolate or lengthened, instead of a flattened or oblate, spheroid. This, however, was afterwards shown to be due to an error in the fundamental measurement; and, in 1735, the comparison of arcs, measured by Maupertuis and others in Lapland, and La Condamine in Peru, established the oblate figure.

Arcs were also measured in Italy, by Boscovich, in 1750; at the Cape, by La Caille, in 1752; and in America, by Mason, in 1764.

The two transits of Venus, in 1761 and 1769, were both, and especially the last, most sedulously observed by astronomers sent to various stations in different parts of the globe, at the expense of the principal governments in Europe; and the important results of the sun's parallax completely settled.

The invention of Hadley's quadrant in 1731 furnished the instrumental means, created as it were for the express purpose of observations on board ship: and the improved lunar tables supplied the data for the easy and complete adoption of the method of lunar distances

for finding the longitude at sea; which was mainly introduced by the zeal and diligence of Dr. Maskelyne, astronomer royal, in setting on foot the "Nautical Almanac," and providing tables and rules adapted to the use of seamen; which, simplified as it was necessary they should be, were yet necessarily founded upon the utmost refinements to which theory and observation had extended.

In 1749, the improvements on watches, for the same important purpose, by Harrison, obtained the Royal Society's medal; and in 1769, after the trial of a long voyage, secured to the ingenious inventor the reward offered by act of parliament. The stimulus thus supplied has been ever since steadily producing a constantly increasing perfection in these machines.

The attraction exercised by large masses of known density, compared with the attraction of the earth, enables us to infer the mean density of the globe. With this view, the attraction of mountains in causing a plumb line to deviate from the perpendicular (which had been noticed by La Condamine in Peru), was investigated by Dr. Maskelyne, in 1774, by observations on the mountain Schehallion in Scotland; and similar observations have been since made by the baron De Zach and others.

An elaborate series of experiments, having the same object in view, though conducted by totally different means, was carried on by Mr. Cavendish in 1798; who estimated the attraction of leaden balls by means of an extremely delicate apparatus. The result agreed very closely with that of the other methods.

In 1787 commenced the series of trigonometrical operations, designed in the first instance merely to connect the observatories of Greenwich and Paris, but which were subsequently extended to the formation of a survey of the whole of Great Britain, under the sanction of the British government, conducted first by general Roy, afterwards by colonels Mudge and Colby, and now extending in Ireland.

Sir W. Herschel had succeeded beyond any previous artist in forming and polishing large metallic specula for telescopes; and, with his gigantic instruments, had the satisfaction of soon adding a new planet to our system. The discovery of Uranus took place in 1781, and was immediately recognised by astronomers throughout Europe. The same eminent observer continued to devote himself to the minute examination of the heavens ; and added immensely to our knowledge of the nebulæ, the appearances and probable physical nature of the sun; and, lastly, of double stars; which, by comparison of observations at considerable intervals, he found, were, in several instances, composed of two bodies, revolving round their common centre of gravity. This discovery was announced in 1803, and has been since abundantly confirmed by the joint labours of his highly distinguished son and Sir J. South; as well as of M. Struve, of Dorpat. Thus is an unlimited extension given to the dominion of the great law of gravitation; even the elliptic forms of the orbits having been, in several instances, ascertained.

Another series of brilliant discoveries were those of the four small planets between the orbits of Mars and Jupiter Ceres, discovered by Piazzi, in 1801, Pallas, by Olbers, in 1802; Juno, by Harding, in 1804; and Vesta, by Olbers, in 1807.

The establishment of the periods of two very remarkable comets has also marked the present century. One observed in 1819 and 1822 was found to resemble

previous appearances. Encke calculated the orbit, and predicted its return in 1825, which was fully verified; and again in 1828 and 1832. It is thus shown to be a small nebulous body, belonging to our system, of a nature, in some sense, intermediate to a comet and a planet. Another body, of a similar nature, was in like manner shown to be a periodical comet by Biela, in 1825.

The last-mentioned discoveries are all of continental origin; and there are numerous other important researches

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