SE C T. important and fublime truths, all closely con

IV.

nected together, by one capital fact, of the reality of which we have daily experience.

NOTE by the EDITORS.

The Author, at the end of this Effay, left fome Notes and Memorandums, from which it appears, that he confidered this last part of his Hiftory of Aftronomy as imperfect, and needing feveral additions. The Editors, however, chofe rather to publish than fupprefs it. It must be viewed, not as a Hiftory or Account of Sir Ifaac Newton's Aftronomy, but chiefly as an additional illustration of those Principles in the Human Mind which Mr. Smith has pointed out to be the universal motives of Philofophical Researches.

THE

PRINCIPLES

WHICH LEAD AND DIRECT

PHILOSOPHICAL ENQUIRIES;

ILLUSTRATED BY THE

HISTORY OF THE ANCIENT PHYSICS.

HISTORY

OF THE

ANCIENT PHYSICS.

ROM arranging and methodizing the Syf tem of the Heavens, Philosophy descended to the confideration of the inferior parts of Nature, of the Earth, and of the bodies which immediately furround it. If the objects, which were here prefented to its view, were inferior in greatness or beauty, and therefore lefs apt to attract the attention of the mind, they were more apt, when they came to be attended to, to embarraís and perplex it, by the variety of their fpecies, and by the intricacy and feeming irregularity of the laws or orders of their fucceffion. The fpecies of objects in the Heavens are few in number; the Sun, the Moon, the Planets, and the Fixed Stars, are all which those philofophers could diftinguish. All the changes too, which are ever obferved in these bodies, evidently arise from fome difference in the velocity and direction of their feveral motions; but the variety of meteors in the air, of clouds, rainbows,

VOL. V.

bows, thunder, lightning, winds, rain, hail, fnow, is vaftly greater; and the order of their fucceffion feems to be ftill more irregular and unconftant. The fpecies of foffils, minerals, plants, animals, which are found in the Wa ters, and near the furface of the Earth, are still more intricately diverfified; and if we regard the different manners of their production, their mutual influence in altering, deftroying, fupporting one another, the orders of their fucceffion feem to admit of an almost infinite variety. If the imagination, therefore, when it confidered the appearances in the Heavens, was often perplexed, and driven out of its natural career, it would be much more exposed to the fame embarrassment, when it directed its attention to the objects which the Earth prefented to it, and when it endeayoured to trace their progrefs and fucceffive revolutions.

To introduce order and coherence into the mind's conception of this feeming chaos of diffimilar and disjointed appearances, it was neceffary to deduce all their qualities, operations, and laws of fucceffion, from thofe of fome particular things, with which it was perfectly acquainted and familiar, and along which its imagination could glide fmoothly. and eafily, and without interruption. But as we would in vain atttempt to deduce the heat of a stove from that of an open chimney, unless

we