the truths which he discovers, and the prospect of a just and grateful posterity, console him for the ingratitude of his contemporaries.

Kepler had obtained pensions which were always ill paid: going to the diet of Ratisbon to solicit his arrears, he died in that city the 15th of November, 1630. He had in his latter years the advantage of seeing the discovery of logarithms, and making use of them. This was due to Napier, a Scottish baron; it is an admirable contrivance, an improvement on the ingenious algorithm of the Indians, and which, by reducing to a few days the labor of many months, we may almost say doubles the life of astronomers, and spares them the errors and disgusts inseparable from long calculations ;-an invention so much the more gratifying to the human mind, as it is entirely due to its own powers: in the arts man makes use of the materials and forces of nature to increase his powers, but here the whole is his own work.

The labours of Huygens followed soon after those of Kepler and Galileo. Very few men have deserved so well of the sciences, by the importance and sublimity of their researches. The application of the pendulum to clocks is one of the most beautiful acquisitions which astronomy and geography have made, and to which fortunate invention, and to that of the telescope, the theory and practice of which Huygens considerably improved, they owe their rapid pro gress.

He discovered, by means of excellent object-glasses which he succeeded in constructing, that the singular appearances of Saturn were produced by a very thin ring, with which the planet is sur rounded his assiduity in observing made him discover one of the satellites of Saturn.

He made numerous discoveries in geometry and mechanics: and if this extraordinary genius had conceived the idea of combining his theorems on centrifugal forces with his beautiful investigation on involutes, and with the laws of Kepler, he would have preceded Newton in his theory of curvilinear motion, and in that of universal gravitation. But it is not in such approximations that discovery consists,

Towards the same time, Hevelius rendered himself useful to astronomy, by his immense labours. Few such indefatigable ob

servers have existed; it is to be regretted that he would not adopt the application of telescopes to quadrants, an invention which gave a precision previously unknown to astronomy.

At this epoch astronomy received a new impulse from the estab lishment of learned societies.

Nature is so various in her productions and phænomena, of which it is so difficult to ascertain the causes, that it is requisite for a great number of men to unite their intellect and exertions to comprehend and develop her laws. This union is particularly requisite when the sciences in extending approximate, and require mutual support from each other.

It is then, that the natural philosopher has recourse to geometry, to arrive at the general causes of the phænomena which he observes, and the geometrician in his turn interrogates the philosopher, in order to render his own investigation useful, by applying them to experience and to open in these applications a new road in analysis. But the principal advantage of learned societies is the philosophical feeling on every subject which is introduced into them, and from thence diffuses itself over the whole nation. The insulated philoso◄ pher may resign himself without fear to the spirit of system; he only hears contradiction at a distance; but in a learned society the shock of systematic opinions at length destroys them, and the desire of mutually convincing each other establishes between the members an agreement only to admit the results of observation and calculation. Thus experience has proved that since the origin of these establishments true philosophy has been generally extended.

By setting the example of submitting every opinion to the test of severe scrutiny, they have destroyed prejudices which had so long reigned among the sciences, and in which the highest intellects of the preceding ages had participated. Their useful influence on opinion accumulated in our own time, with an enthusiasm which at other periods would have perpetuated them. Finally, it is among them, or by the encouragement they offer, that those grand theories have been formed which are placed above the reach of the vulgar by their comprehensiveness; and which, extending themselves by their numerous occasions in which they are applicable, to nature and to the arts, are inexhaustible sources of delight and intelligence.

Of all the learned societies, the two most celebrated for the number and importance of their discoveries in the sciences, and

terrestrial meridian, and of the pendulum, multiplied in different parts of the globe, of which France gave the example, by measuring the whole arc of the meridian, which crosses it, and by sending the academician to the north and to the equator, to observe the magnitude of these degrees, and the intensity of the force of gravity. The arc of the meridian, comprised between Dunkirk and Barcelona, determined by very precise observations, and forming the base of the most natural and simple system of measures; the voyages undertaken to observe the two transits of Venus over the Sun's disk, in 1761 and 1769, and the exact knowledge of the dimensions of the solar system, which has been derived from these voyages; the inven tion of achromatic telescopes, of chronometers, of the sextant and repeating circle, the discovery of the planet Uranus, by Herschel, in 1781; that of its satellites, and of two new satellites of Saturn, due to the same observer, all the astronomical theories being brought to perfection, and all the celestial phænomena, without exception, being referred to the principle of universal gravitation:-these, with the discoveries of Bradley, are the principal obligations which astronomy owes to England, which, with the preceding, will always be considered as constituting the most glorious epoch of the science. [La Place, Exposition du Système du Monde.]

CHAPTER IV.

GENERAL NOTICES ON ASTRONOMY

To the preceding observations of La Place, the Editor of the

present work has thought right to subjoin the following singular or learned opinions of several of the most esteemed writers on the subject.

Professor Playfair, in an article inserted in the Edinburgh Philosophical Transactions, supports the very high pretensions of the Bramins to Astronomy, and conceives that they are in possession of some observations not less than five thousand years old. Mr. Costard, in a paper on the Chinese Chronology and Astronomy, print

ed in the Transactions of the Royal Society for 1747, and Mr. Bentley, in Vol.VI. of the Asiatic Researches, offer cogent arguments against any such antiquity of Astronomical knowledge in the East: the latter indeed goes so far as to make the principal tables of the Bramins, which they call Surya Siddhanta, not more than about 733 years old.

Newton thinks that the constellations were arranged by Chiron when the solstitial and equinoctial points were in the middle of the respective constellations. Phil. Trans. for 1725.

Mr. Wall, in a paper on astronomical symbols, printed in the Manchester Memoir, Vol. I. 243, derives (Mercury), from the caduceus; (Venus), from the sistrum; (Mars), from the shield and spear; (Jupiter), from Jr, the contraction or first and last letters of the word; h(Saturn), from the sickle. Frisch, however, derives 2 from lightning with the eagle.

Alexandre and Baliani thought the Earth revolved around the Moon. Marian.

In the account of Gail's Memoir on Synesius's Astrolabe, Maps are attributed to Anaximander 600 years before Christ. M. Inst. V.34.

According to Plutarch, Heraclides and Ecphantus attributed to the Earth a diurnal motion only.

Astronomy was introduced into Spain by the Moors in 1201.

The Mexicans when discovered by the Spaniards had years of 365 days, and added 12 days at the end of every period of 52 years. Robison. Young's Nat. Phil.-Editor.

CHAPTER V.

THE CELESTIAL WORLD DISCOVERED; OR, CONJECTURES CONCERNING THE INHABITANTS, PLANTS, AND PRO

DUCTIONS, OF THE WORLD IN THE PLANETS;

Written in Latin by CHRISTIANUS HUYGENS, and inscribed to his brother CONSTANTINE HUYGENS, late Secretary to his Majesty King William. 8vo. with five cuts of Illustration.

THE ingenious author of this discourse, having spent much time, and taken great pains in making celestial observations and discoveries by telescopes of the largest sizes, and other instruments, and having moreover acquainted himself with the latest and best observations and discoveries made by other modern Astronomers; and having well weighed and considered the import and significancy of them, comes in this book to acquaint his brother the heer Constantine Huygens, (who was also a great lover of these inquiries, and who was the person that furnished him with the excellent telescopes he made use of, wrought with his own hand, wherein he had for his diversion acquired an extraordinary art and dexterity, unknown to any besides himself) and by the publication of it, if he thought fit likewise to acquaint the learned world, what upon the result of all, his opinion and belief was concerning the form, structure, and fabrick of the universe, or the whole visible world, and the reasons and arguments that induced him thereunto, which he hopes may seem reasonable enough to men skilled in geometrical, and astromical sciences; such as he wishes his readers may be. But because he was well aware that many of them might be persons of differing qualiti cations, and such as could not, or would not understand the cogency of them, or from prepossession would endeavour to carp at, and make arguments against the whole doctrine there delivered, therefore he endeavours to enumerate and obviate such as are most likely to be produced for that end. The first of which he conceives, may be of such as are ignorant of mathematical knowledge, who will be apt to represent it as a whimsey only of a disturbed brain, they