hereto, St. Augustine answers this very doubt concerning the motion of the Heavens. d❝ Some of the brethren (faith he) move a queftion, whether the Heavens ftand ftill or are moved; because, fay they, if they are moved, how is it a firmament? and if they stand ftill, how do the ftars, which are believed to be fixt in them, revolve from eaft to weft, the northern ftars defcribing leffer circles near the pole?" -To which, faith he, I answer, "That these things do greatly require feveral fubtle and laborious reafons, to discover truly whether the matter be fo, or not fo. For the entering upon, and difcuffing of which, I have neither time, nor is it fit it fhould be done to fuch as we defire to inftruct in the way of falvation, for the neceffary benefit of the holy church."

Having thus answered the objections from fcripture, I fhall in the last place confider those brought from sense and philofophy.

The objections from fenfe is, That we fee the heavenly bodies actually to move, and therefore ought to believe they do fo. But there is no

Auguft. de Genefi ad Literam, I、 ii. 10.

As

weight in this, because whether we ourselves, or the object moveth, it amounts to the fame. is manifeft to any one carried in a boat or chariot ; the progreffive motion of which produceth the appearance of a regreffive motion in the unmoved objects we look upon; according to Virgil's defcription of Æneas and his company's leaving their port.

Provehimur portu, terræque urbefque recedunt.

i. e. " Both lands and towns receded when we left our port." As for the reafon hereof, I fhall refer to the opticians, particularly the famous Kepler, who in his Optices Aftronom. hath defignedly handled this point.

The objections from philofophy are too numerous to be distinctly answered, especially fuch as feem very frivolous; particularly thofe grounded on a fuppofition of the verity of the Ariftotelian philofophy; as the immutability and incorruptibility of the Heavens, &c. For anfwers to which I fhall refer the reader to Galilæo's Syftema Mundi: but for fuch objections as feem to have some reason in them, they are chiefly these, That

Æneid. 1. iii. car. 72.

if the Earth be moved from W. to E. a bullet fhot weftward would have a farther range, than one shot Eastward; or if fhot N. or S. it would mifs the mark; or if perpendicularly upright, it would drop to the westward of the gun. That a weight dropped from the top of a tower would not fall down juft at the bottom of the tower, as we see it doth. That birds flying towards the E. would be hindered in their flight, but forwarded in flying the contrary way; with much more to the fame purpose. But not to enter into a detail of answers that might be given to the laws of motion, and the rules of mechanics and mathematicks, I fhall only make use of the most ingenious Galilæo's plain experiment, which answereth all, or most of the objections. f "Shut, faith he, yourfelf up with your friend in the great cabin of a fhip, together with a parcel of gnats and flies, and other little winged creatures. Procure alfo a great tub of water, and put fishes therein. Hang alfo a bottle of water up, to empty itself drop by drop into another fuch bottle placed underneath, with a narrow neck. Whilft the ship lies ftill, diligently obferve how those little winged creatures fly with the like fwiftnefs towards every part of the cabin; how

Syftem. Mund. Diat. 2.

the

the fishes fwim indifferently towards all fides; and how the defcending drops all fall into the bottle underneath. And if you throw any thing to your friend, you need ufe no more force one way than another, provided the diftances be equal. And if you leap, you will reach as far one way as the other. Having obferved these particulars whilft the fhip lies ftill, make the ship to fail with what velocity you please, and so long as the motion is uniform, not fluctuating this way and that way, you fhall not perceive there is any alteration in the aforefaid effects; neither can you from them conclude, whether the ship moveth or ftandeth ftill. But in leaping you shall reach as far on the floor as you did be fore; nor by reafon of the ship's motion, shall you make a longer leap towards the poop than the prow, notwithstanding that whilst you were up in the air, the floor under your feet had run the contrary way to your leap. And if you caft any thing to your companion, you need ufe no more ftrength to make it reach him, if he fhould be towards the prow, and you towards the poop, than if you ftood in a contrary pofition. The drops fhall all fall into the lower bottle, and not one towards the poop, although the ship shall have run many feet, whilft the drop was in the air. The fishes in the water fhall have no more trouble

N 4

trouble in swimming towards the forepart of the tub, than towards the hinder part, but shall make towards the bait with equal fwiftness, on any fide of the tub. And lastly, the gnats and flies fhall continue their flight indifferently towards all parts, and never be driven together towards the fide of the cabin next the prow, as if wearied with following the swift motion of the fhip. And if by burning a few grains of incense, you make a little fmoak, you fhall perceive it to afcend on high, and hang like a cloud, moving indifferently this way and that, without any inclination to one fide more than another. The cause of which corefpondence of the effects, is, that the fhip's motion is common to all things contained in it, and to the air alfo: I mean when thofe things are fhut up in the cabin: but when they are above deck in the open air, and not obliged to follow the fhip's course, differences more or lefs may arife among the forenamed effects."

Thus Galilæo by this one observation hath answered the most confiderable objections deduced from philofophy against the motion of the earth. And thus much fhall fuffice for the explanation and proof of the Copernican fyftem; especially that part of it relating to the Solar fyftem.