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An Attempt to Prove the Motion of the Earth by Observations
(Continued)

For supposing all the fixt Stars as so many Suns, and each of them to have a Sphere of activity or expansion proportionate to their solidity and activity, and a bigger and brighter bodied Star to have a proportionate bigger space or expansion belonging to it, we should from the knowledge of their Diameters and brightnesses be better able to judge of their distances, and consequently assign divers of them other magnitudes then those already stated: Especially since we now find by observations, that of those which are accounted single Stars, divers prove a congeries of many Stars, though from their near appearing to each other, the naked eye cannot distinguish them; Such as those Stars which are called Nebulous, and those in Orion Sword, and that in the head of Aries, and a multitude of others the Telescope doth now detect. And possibly we may find that those twenty magnitudes of Stars now discovered by a fifteen foot Glass, may be found to increase the magnitude of the Semidiameter of the visible World, fourty times bigger then the Copernicans now suppose it between the Sun and the fixt Stars, and consequently sixty four thousand times in bulk.

And if a Telescope of double or treble the goodness of one of fifteen should discover double or treble the said number of magnitudes, would it not be an Argument of doubling or trebling the former Diameter, and of increasing the bulk eight or twenty seven times. Especially if their apparent Diameters shall be found reciprocal to their Distances (for the determination of which I did make some observations, and design to compleat with what speed I am able.)

But to digress no further, This grand object ion of the Anticopernicans, which to most men seem'd so plausible, that it was in vain to oppose it, though, I say, it kept me from declaring absolutely for the Copernican Hypothesis, yet I never found any absurdity or impossibility that followed thereupon: And I alwayes suspected that though some great Astronomers had asserted that there was no Parallax to be found by their observations, though made with great accurateness, there might yet be a possibility that they might be mistaken; which made me alwayes look upon it as an inquiry well worth examining: first, Whether the wayes they had already attempted were not subject and lyable to great errors and uncertainties: and secondly, Whether there might not be some other wayes found out which should be free from all the exceptions the former were incumbred with, and be so far advanced beyond the former in certainty and accurateness, as that from the diligent and curious use thereof, not only all the objections against the former might be removed, but all other whatsoever that were material to prove the ineffectualness thereof for this purpose.

I began therefore first to examine into the matter as it had already been performed by those who had asserted no sensible Parallax of the annual Orb of the Earth, and quickly found that (whatever they asserted) they could never determine whether there were any or no Parallax of this annual Orb; especially if it were less then a minute, which Kepler and Riccioli hypothetically affirm it to be: The former making it about twenty four Seconds, and the latter about ten.

For though Ticho, a man of unquestionable truth in his assertions, affirm it possible to observe with large Instruments, conveniently mounted and furnished with sights contrived by himself (and now the common one s for Astronomical Instruments) to the accurateness of ten Seconds; and though Riccioli and his ingenious and accurate Companion Grimaldi affirm it possible to make observations by their way, with the naked edge to the accurateness of five Seconds; Yet Kepler did affirm, and that justly, that 'twas impossible to be sure to a less Angle then 12 Seconds: And I from my own experience do find it exceeding difficult by any of the common sights yet used to be sure to a minute. I quickly concluded therefore that all their endeavours must have hitherto been ineffectual to this purpose, and that they had not been less imposed on themselves, then they had deceived others by their mistaken observations.

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