LET. II. OF THE EARTH. 2$

ing into those particulars till you are furtheradvanced in the science, and properly preparedto understand them.

That the true magnitude can‘be determinedis not to be doubted. For the form of the earthbeing once known, its bqlk could not long re-main a secret. Accordingly we find that severalof the ancient philosophers, wfio lived soonafter the time of those before mentioned, at-tempted the solution of this curious problem.And though the measures they have given areconsiderably wide of the truth, as well as dif Tferent from each other, yet this was owing moreto the inaccuracy of their instruments, and thewant of a sufficient stock of mathematicalknowledge, than to any real difficulty or im-practicability in the thing itself.

But let us leave this subject for the present,and proceed to another of equal importance.—Ihave before proved to you, from the most in-dubitable arguments, that the earth is a globu-lar body, unsupported by pillars of a bottomlessfoundation, as many have absurdly imagined:I shall now give you some account of its motion;a thing more remote from vulgar apprehensionthan the former, though equally certain and de-monstrable. And, in order that you may ob-tain as clear and comprehensive an idea of thesubject as possible, we will first take a view ofuniverse in general, and of that part of it in

particular.