To illustrate the particular I am discoursing of, I'll endeavour to detect the unlucky influence of sensitive prejudice by a double instance; the free debate of which I conceive to be of importance, though hitherto for the most part obstructed, by the peremptory conclusion of a faculty which I shall make appear to have no suffrage in the case of either: and the pleasantness and concernment of the theories, if it be one, I hope will attone the digression.
§. 2. First, it is generally opinioned that the Earth rests as the world's centre, while the heavens are the subject of the universal motions; and, as immoveable as the Earth, is grown into the credit of being proverbial. So that for a man to go about to counter-argue this belief, is as fruitless as to whistle against the winds. I shall not undertake to maintain the paradox, that confronts this almost Catholic opinion. Its assertion would be entertained with the hoot of the rabble: the very mention of it as possible, is among The most ridiculous; and they are likely most severely to judge it, who least understand what it is they censure. But yet The patronage of as great wits, as it may be e're saw the sun, such as Pythagoras, Descartes, Copernicus, galileo, More, Kepler, and generally the vertuosi of the awakened world, hath gained it a more favourable censure with learned mankind; and advanced it far above either vain, or contemptible. And if it be a mistake, it's only so: there's no heresy in such an harmless aberration; at the worst, with the ingenuous, the probability of it will render it a lapse of easy pardon.
Now whether the Earth move or rest, I undertake not to determine. My work is to prove, that the common inducement to the belief of its quiescence, the testimony of sense, is weak and frivolous: to the end, that if upon an unprejudiced trial, it be found more consonant to the astronomical phenomena; its motion may be admitted, notwithstanding the seeming contrary evidence of unconcerned senses. And I think what follows will evince, that this is no so absurd an hypothesis, as vulgar philosophers acount it; but that, though it move, its motion must needs be as insensible, as if it were quiescent; and the assertion of it would than be as uncouth and harsh to the sons of sense, that is, to the generality of mankind, as now it is.
That there is a motion, which makes the vicissitudes of day and night, and constitutes the successive seasons of the year; sense may assure us; or at least the comparative judgment of an higher faculty, made upon its immediate evidence: but whether the sun, or Earth, be the common movent, cannot be determined but by a further appeal. If we will take the literal evidence of our eyes, the ethereal coal moves no more than this inferior clod doth: for whereever in the firmament we see it, it's represented to us, as fixed in that part of the enlightened hemisphere. And though an after account discover, that he hath changed its site and respect to this our globe; yet whether that were caused by its translation from us, or ours from it, sense leaves us in an ignoramus: so that if we are resolved to stand to its verdict, it must be by as great a miracle if the sun ever move, as it was that it once rested, or what ever else was the subject of that supernal change. And if upon a mere sensible account we will deny motion to the Earth; upon the same inducement we must deny it the sun; and the heavens will lose their first moveable. But to draw up closer to our main design, we may the better conceive that, though the Earth move, yet its motion must needs be insensible; if we consider that in these cases relating to our purpose, motion strikes not the sense.
(1.) Then if the motion be very slow, we perceive it not. We have no sense of the accretive motion of plants or animals; and the sly shadow steals away upon the dial; and the quickest eye, can discover no more but that 'tis gone. Which insensibility of slow motions I think may thus be accounted for; motion cannot be perceived without the perception of its terms, viz. The parts of space which it immediately left, and those which it next acquires. Now the space left and acquired in every sensible moment in such slow progressions, is so inconsiderable, that it cannot possibly move the sense; (which by reason either of its constitutional dulness, or the importunity of stronger impressions, cannot take notice of such parvitudes) and therefore neither can the motion depending thereon, be any more observable, than we find it.
2. If the sentient be carried passibus equis with the body, whose motion it would observe; (supposing that it be regular and steady) in this case the remove is insensible, at least in its proper subject. We perceive not a ship to move, while we are in it; but our sense transfers its motion to the neighbouring shores, as the poet, littis campiq; recedunt. And I question not, but if any were born and bred under deck, and had no other information but what his sense affords; he would without the least doubt or scruple, opinion, that the house he dwelt in, was as stable and fixed as ours. To express the reason according to the philosophy of Descartes, I suppose it thus: motion is not perceived, but by the successive strikings of the object upon divers filaments of the brain; which diversify the representation of its site and distance. But now when the motion of the object is common with it, to ourselves; it retains the same relation to our sense, as if we both rested: For striking still on the same strings of the brain, it varies not its site or distance from us; and therefore we cannot possibly perceive its motion: nor yet upon the same account our own; least of all, when we are carried without any conamen and endeavour of ours, which in our particular progressions betrayes them to our notice.
Now then, the Earth's motion (if we suppose it to have any) hath the concurrence of both, to render it insensible; and therefore we need no more proof to conclude the necessity of its being so.
For though the first seems not to belong to the present case, since the supposed motion will be near a thousand miles an hour under the equinoctional line; yet it will seem to have no velocity to the sense any more than the received motion of the sun and for the same reason. Because the distant points in the celestial expanse (from a various and successive respect to which the length, and consequently the swiftness of this motion must be calculated) appear to the eye in so small a degree of elongation from one another, as bears no proportion to what is real. For since the margin of the visible horizon in the heavenly globe is parallel with that in the earthly, accounted. But 120 miles diameter; sense must needs measure the azimuths, or pertical circles, by triplication of the same dianteter of 120. So that there will be no more proportion betwixt the sensible and real celerity of the terrestrial motion, than there is between the visible and rational dimension of the celestial hemisphere, which is none at all.
But if sensitive prejudice wili yet confidently maintain the impossibility of the hypothesis, from the supposed unwieldiness of its massy bulk, grounded on our experience of the ineptitude of great and heavy bodies to motion: I say this is a mere imposture of our senses, the fallacy of which we may avoid, by considering; that the Earth may as easily move, notwithstanding this pretended indisposition of its magnitude, as those much vaster orbs of sun and stars. He that made it, could as well give motion to the whole, as to the parts; the constant agitation of which is discovered in natural productions: and to both, as well as rest to either: neither will it need the assistance of an intelligence to perpetuate the begun rotation: since according to the indispensible law of nature (that every thing should continue in the state wherein it is, except something more powerful hinder it) it must persevere in motion, unless obstructed by a miracle. Neither can gravity, which makes great bodies hard of remove, be any hindrance to the earths motion: since even the Peripatetic maxime, nihil gravitat in suo loco, will exempt it from the indisposition of that quality; which is nothing but the tendency of its parts, which are ravished from it, to their desired centre.
And the French philosophy will inform us, that the Earth as well as other bodies is indifferent in itself to rest, or its contrary.