ledge which are placed beyond the pale of absolute certainty. To supply fixed principles on which the probability of events may be estimated, and even expressed by mathematical formulæ, is of all other inventions one of the most happy and important: it tends to put us in possession of the most sound principles on which to discriminate truth from error; and embraces as well the chances of future contingencies, as the probabilities of error in the present and the past, from the fallibility of observation and testimony; and has been well designated by an able writer, 66 a fortunate sup

plement to the imperfection of our nature." The idea was first started by Pascal ; it was successively improved upon by Bernoulli, Euler, and Lagrange; but owes its full development entirely to Laplace.

Laplace, in conjunction with Lavoisier, made extensive researches on the theory of heat, and especially the dilatations of bodies: his investigations on the atmospheric refraction, on capillary attraction, on the barometical measurement of heights, on electricity, on the velocity of sound, on molecular action, and on the properties of gases, most of which occupy parts of the different supplements in the Mécanique Céleste, show at once how multifarious were his enquiries, and with what unity of purpose he carried them on, at length embodying them under the laws of a comprehensive analysis, to stand as parts in the great theory of the material world which he was engaged in completing; and which, in its systematic uniformity, enables us to gain a nearer approach to the apprehension of that all. perfect uniformity of design which we cannot doubt is the real pervading principle of the whole fabric of nature: which, we must confess, no human powers will probably ever be able completely to analyse, but which, at every approach we can successively make, appears more and more distinctly invested with this never-failing attribute.

As a writer Laplace shines among his eloquent contemporaries with unusual brilliancy. His more popular

HISTORICAL VIEW OF THE

productions on philosophical subjects, are composed i an enviable union of the most complete perspicuity, all that elegance of style which, without being disti by attempts at ornament unsuited to the subject, once illustrates it, and renders it inviting to the gene reader. Like his great predecessor Newton, he evin most sensibly the humility of true intellectual supe riority; and the last sentence he uttered was, we know is little, and what we are ignorant of is in

mense."

"What

disti

Laplace, born in 1749, was at an early age guished 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 the 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 to the age, it is a far more wonderful production than the Almegest of the eighteenth century; but, relatively its prototype. The original discoveries of the author embodied in it, are the solutions of the highest problems I which the mechanism of the universe presents; many of them had baffled the attempts of all preceding ma thematicians, and some received not only their solution, was fortunate in enjoying, through a long life, the but their first suggestion, from Laplace himself. He situation and the means for the uninterrupted prose cution of abstruse research: his residence at Arcueil was the centre of attraction to all the mathematical philo sophers of Europe. He died in 1827, when his varied labours had been brought nearly to their complete per

fection.

The works of Laplace will be his enduring monument to the world; but to the astronomer, even of the re yet more enduring kind, perpetually exhibited. The motest age, there will be a memorial of a loftier, and the irregularities of the planetary motions stability of the system is secured, and o surprisingly established, will be recog

e 208

ised in the observations of the most distant epochs, and he 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 ders it in 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 reguelated 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.

ser of

he bea

ed the

ainder of Lecuted by century

derful p

coveries

verse pr

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 the 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.

f all p

t only d

place

hal

inter

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

HISTORICAL VIEW OF THE

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

0

We have alluded to Halley's labours. to them the glory of being the first to predi turn of a comet. Having noticed an agreem elements of several which had appeared at periods, he concluded them to be reappearan same body, obeying the law of an elliptic or foretold a return in 1758, which was completely

Bradley, associated with Molyneux, comme 1725, that valuable series of observations whic the discovery of the aberration and the nutatio earth's axis. The former a consequence of t velocity of light, the latter of gravitation.

The measures of the arc of the meridian we repeated with increased accuracy in France, by l and Cassini, but seemed to lead to the strange a radoxical result of the earth's figure being a pr lengthened, instead of a flattened or oblate, spheroid however, was afterwards shown to be due to an e the fundamental measurement; and, in 1735, the parison of arcs, measured by Maupertuis and oth Lapland, and La Condamine in Peru, oblate figure.

establishe

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

The two transits of Venus, in 1761 and 1769, both, and especially the last, most sedulously obse by astronomers sent to various stations in different p of the globe, at the expense of the principal gove ments in Europe; and the important results of the su parallax completely settled.

Inished the instrumental means, created as it were The invention of Hadley's quadrant in 1731 f the express purpose of observations on board ship: a the improved lunar tables supplied the data for the ea mplete adoption of the method of lunar distand

and

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 gener Roy, afterwards by colonels Mudge and Colby, and n extending in Ireland.