SECT qualities, after its inertness, that which is moft IV. familiar to us. We never act upon it without

having occafion to obferve this property. The law too, by which it is fuppofed to diminish as it recedes from its centre, is the fame which takes place in all other qualities which are propagated in rays from a centre, in light, and in every thing elfe of the fame kind. It is fuch, that we not only find that it does take place in all fuch qualities, but we are neceffarily determined to conceive that, from the nature of the thing, it must take place. The oppofition which was made in France, and in fome other foreign nations, to the prevalence of this fyftem, did not arife from any difficulty which mankind naturally felt in conceiving gravity as an original and primary mover in the constitution of the univerfe. The Cartefian fyftem, which had prevailed fo generally before it, had accustomed mankind to conceive motion as never beginning, but in confequence of impulfe, and had connected the defcent of heavy bodies, near the furface of the Earth, and the other Planets, by this more general bond of union; and it was the attachment the world had conceived for this account of things, which indifpofed them to that of Sir Ifaac Newton. His fyftem, however, now prevails over all oppofition, and has advanced to the acquifition of the most universal empire that was ever established in philofophy. His prin

ciples,

IV.

ciples, it must be acknowledged, have a degree SE C T. of firmnefs and folidity that we should in vain look for in any other fyftem. The most sceptical cannot avoid feeling this. They not only connect together moft perfectly all the phænomena of the Heavens, which had been obferved before his time; but those also which the perfevering industry and more perfect inftruments of later Aftronomers have made known to us have been either easily and immediately explained by the application of his principles, or have been explained in confequence of more laborious and accurate calculations from these principles, than had been inftituted before. And even we, while we have been endeavouring to reprefent all philofophical fyftems as mere inventions of the imagination, to connect together the otherwife disjointed and difcordant phænomena of nature, have infenfibly been drawn in, to make ufe of language expreffing the connecting principles of this one, as if they were the real chains which Nature makes ufe of to bind

together her feveral operations. Can we wonder then, that it fhould have gained the general and complete approbation of mankind, and that it fhould now be confidered, not as an attempt to connect in the imagination the phænomena of the Heavens, but as the greatest discovery that ever was made by man, the difcovery of an immenfe chain of the moft

THE

PRINCIPLES

WHICH LEAD AND DIRECT

PHILOSOPHICAL ENQUIRIES;

ILLUSTRATED BY THE

HISTORY OF THE ANCIENT PHYSICS.