I am oblig'd to M. _Du Puis_, said _La Foret_, for having started this Subject of Conversation; for I had been a long time desirous to know what was meant by the _Bissextile_ Year, by _Old_ and _New Style_, and what was the real Cause of all those Alterations. They would not be satisfy'd till I had at several times explain'd to them the Meaning of the Terms _Epact_, _Golden Number_, _Solar Cycle_, _Roman Indiction_, _Ides_, _Calends_, and every thing almost that is necessary to be known for the Composition of an Almanack. What they most wonder'd at was, when I assur'd them that the Sun, which to us seem'd so small, is absolutely bigger than the whole Earth. Really, said _La Foret_, this is beyond Imagination, and I can't think that all the Stories told us of these things are any better than Dreams. _Du Puis_, who aggravated every Objection made by his Comrade, presum'd to tell me, that I talk'd very much at random, because I maintain'd the Truth of it; so that I was under a Necessity, tho' sorely against the Grain, to proceed to some Eclaircissements for their Satisfaction.
I confess, said I, that 'tis impossible to determine the exact Dimensions of the Celestial Luminaries; and all that have pretended to it have been presumptuous Impostors. The Instruments we make use of to measure the Parallax of the Sun, are too small, and too ill divided, considering the prodigious Distance of that Planet from the Earth. I never yet saw an Astrolabe divided into Minutes, tho' it were necessary it should be divided into Seconds, and perhaps into smaller Parts, which is impossible, or it would be too large for the Purpose. And as a Proof how liable we are to be mistaken for want of it, the most exact Astronomers, who, not content with the Theory, have gone about to reduce this Query to Practice, have been so grossly deceiv'd, that the wide Difference of one Man's Opinion from another, is enough to bring the Understanding of those Men in question, who would palm their Conjectures upon the World for real Truths. _Tycho Brahe_, who seems to have made a Circuit round the Heavens, as _Christopher Columbus_ did round the Earth, affirms, that the Sun is 139 times bigger than the Globe which we inhabit. _Copernicus_ makes the Number to be 162; _Ptolemy_, 166; Father _Scheiner_, 434; _Wendelinus_ 4096: And one of my Tutors affirm'd it to be three Millions of times bigger than the Earth. Therefore we know nothing positively of its Bigness, but that 'tis much larger than this great Body, how big soever it appears to us, is a Certainty. For in the first Place, supposing it to be of equal Bigness with the Earth, 'tis evident that its Rays in their Passage over the exterior Parts of this Terrestrial Sphere, would leave a Cylinder of Obscurity beyond it, whose Sides would be parallel, so that the Planets, in their way thro' that Opaque, receiving no Light, and having none of their own, would be eclips'd. If the Sun was Smaller than the Earth, its Rays, after having glanced over the Earth, would grow wider, and form a Cone cut off by a Shadow, with its Basis in the Firmament, and the Top on the Part of the Earth opposite to the Sun; the Consequence of which is that a still greater part of the Heavens would be darken'd, and all the Planets there, as was just now observ'd, could give no Light. The only Planet that ever we see eclips'd is the Moon; it appears, therefore, that the Sun must be incomparably bigger than the Earth, because its Rays, when they have pass'd over this great Mass, unite again a little above the Moon, where the Cone, form'd by the Shadow of the Earth, ends in a Point. To illustrate this Explanation, I made a Figure in the Sand.