ASTRONOMY.

movelh, &c. making that to he the act of the sun in vulgar dis-course, which they, contend to be in reality performed by theearth. And if philosophers, apd others, did not thus express them-selves according to the appearance of tilings, and men’s vulgar ap-prehensions of them, it would need a comment, and they mustexplain themselves everv time they speak, in order to their hyingunderstood.” The objection against the Newtonian system fromsense is, That all the heavenly bodies appear from the earth tomove, and consequently their motion is real. But nothing canbe more absurd than this conclusion ; as is sufficiently plain fromthe apjiearances observed by them who sail in a ship, or are carriedin a chariot, tliQ progressive motion of which produced) the ap-pearance of a regressive motion in the unmoved objects, accord-ing to Virgil’s description of Tineas and his company leavingtheir port:—

“ Provehimur portu, terrxque urbesque rccedunt.”

rE.vEit). lib. iii. 72,

i.e. Both'lands and cities receded when we left the port.

The principal objections drawn from philosophy against this sys-tem are the following: If the earth moved from west to east, abullet shot westward would have a farther range than one shoteastward ; or if shot north or south, it would miss the mark, or itperpendicularly upright, it would drop to the westward of thegun. That a weight dropped front the top of a tower would notfall down just at the bottom of the tower, as it is known to do.That birds dying towards the easttvould be hindered in their flight,but forwarded in Hying the contrary way, &c. &c- But let theunprejudiced person who has considered these as real objections tothe Copernican system, read over attentively the following plain ex-periment of Galileo ; and it is impossible that he should afterwardsbelieve them to be at all decisive against the present almost univer-sally received system of Astronomy. “ Shut, (saith he, System.Mundi, Dial. 2. and Derham’s Astro-Theology, pp. 33—36,)yourself up with your friend in the great cabin of a ship togetherwith a parcel of gnats and flies, and other winged creatures. Pro-cure also a great tub of water, and put fishes therein. Hang alsoa bottle of water up, to empty itself drop by drop into anothersuch bottle placed underneath with a narrow neck. Whilst theship lies still, diligently observe how those little winged creaturesfly with the like swiftness towards every part of the cabin ; how thefishes swim indifferently towards all sides; and how the descend-ing drops all fall into the bottle underneath. And if you throwany thing to your friend, you need use no more force one waythan another, provided the distances be equal. And if you leap,you will reach as far one way as the other. Having observedthese particulars whilst the ship lies still, make the ship to sail withwhat velocity you please, and so long as the motion is uniform,not fluctuating this way and that way, you shall not perceive(here is any alteration in the aforesaid effects ; neither can youfrom them conclude whether the ship moveth or standeth still.But in leaping you shall reach as far on the floor as you did be-fore ; nor by reason of the ship’s motion, shall you make a longerleap towards the poop than the prow, notwithstanding that w'hilstyou were up in the air, the floor under your feet had rim the con-trary way to your leap. And if you cast any thing to your com-anion, you need use no more strength to make it reach him, ife should be towards the prow, and you towards the poop, than ifyou stood in a contrary position. The drops shall all fall into thelower bottle, and not one towards the poop, although the ship shallhave run many feet, whilst the drop was in the air. The fishes inthe water shall have no more trouble in swimming towards thefore-part of the tub, than towards the hinder part, imt shall maketowards the bait with equal swiftness, on any side of the tub. Andlastly, the gnats and flies shall continue their flight indifferently to-wards all parts, and never be driven together towards the side ofthe cabin next the prow, as if wearied with following the swiftmotion of the ship. And if by burning a few grains of incense,you make a little smoke, you shall perceive it to ascend on high,and hang like a cloud, moving indifferently this way and that,without any inclination to one side more than another. Thecause of which correspondence of the effects, is, that the ship’smotion is common to $11 things contained in it, and to the air also:1 mean when those things are shut up in the cabin : but whenthey are above deck in the open air, and not obliged to followthe ship’s course, differences more or less may arise among thefoicuamed effects.” Thus Galileo by this one observation hath

answered the most considerable objections deduced from phi.losophy against the earth’s motion ; for since repeated observa-tions attest the above and similar remarkable effects in the differ-ent articles appertaining to a ship or carriage, whether in slowor rapid motion, provided it be without fluctuation ; so may ourglobe have a rapid motion round the sun without the possibilityof its being perceived by any person or animal belonging to it.

Sect III. Of the Orbits and Motions of the PrimaryPlanf.ts.

(52.) That tliesun, and not the earth, is the centre of the planetarymotions is sufficiently evident from their very great irregularity asseen from our globe ; for sometimes they move forward accord-ing to the order of the signs, at other limes they appear to havescarcely any motion at all, in certain points of the Zodiac they arestationary tor a short time, and once every synodic revolutionhave a retrograde motion. Again, if the planets turned round theearth, as their centre, they could never appear to us to be retro-grade, nor even stationary ; but their geocentric circle in the Zo-diac would be exactly described like that of the moon. In theirapogee their motion, though then the slowest, would stillbe direct; and as they moved from apogee to perigee their directmotion would be continually accelerated, and in moving fromperigee to apogee as constantly retarded. Besides, astronomers,in finding the geocentric place of a planet, first ascertain itsplace as seen from the sun, as a centre, and from it (by the help ofa trigonometrical series of proportions founded entirely upon, andmathematically demonstrated to result from, the sun’s being in tin}centre of their orbit,) have calculated the place of the planet asseen from the earth; and these calculations are known to corres.pond continually with observation to the precision of a very fewseconds of a degree ; which it is impossible could be the case ifthe basis upon which these calculations were grounded was a falseone. Again, it is certain that wherever the sun be placed the orbitof Venus surrounds him; and consequently V enus when she de-scribes this orbit actually turns round the sun ; for this planet hasbeen observed to be further from the earth than the sun is, andalso nearer to us than we are to the sun. That Venus is sometimesfarther from us than we are from the sun is plain from hence, thatwhen she is in conjunction with the sun, that is, when she is seenfrom the earth nearly in the same part of the heavens that the sunis in, her lucid disk appears in a full and round figure: for since allthe planets receive all the light they have from the sun, it is evi-dent that that half of her giohe only which is turned toward thesun will be illuminated, anil that which is turned from him conse-quently involved in darkness ; and therefore when she shines witha lull and round face, that side of her which is toward the sun isalso towards the earth ; and therefore at that time she must befarther from us than we are from the sun, for in no other positioncould her illuminated face be turned towards us when she is inconjunction with the sun. That Venus is also sometimes nearerto us than we are to the sun is evident from hence ; that some-times when she is in conjunction with the sun, she either entirelydisappears, or if she is visible, she appears finely horned, and takesexactly the shape of the moon two or three days before and afterthe conjunction. And therefore her illuminated disk is eitherwholly turned from the earth, or only a very small portion of itturned towards the earth; and therefore at that time she must ne-cessarily be placed between the sun and us. Besides, if Venus moved round the earth, she would be seen as often in oppositionas in conjunction with the sun ; but she never recedes from him be-yond a certain distance, which is about 47 degrees ; consequentlythe sun, and not the earth, is the centre of her motion. After thesame manner Mercury always keeps near the sun, and is neverseen from him further than about 28 degrees, which is very littlemore than half the greatest elongation of Venus . He also puts onthe same phases with Venus in similar parts of his orbit, as seenfrom the earth, lienee it is evident that Mercury moves roundthe sun in a less orbit than Venus , and that’ the orbit of the earthincludes both their orbits within it Mars is not like Mercuryand Venus , for he often comes in opposition to the sun, and risesin the east when the sun sets in the west, and therefore his orbitincludes that of the earth within it, and not only the earth’s orbit,but also the body of the sun ; for Mars when he is seen near theconjunction with the sun, if he were between the sun and us,would either quite disappear, or appear horned as the moon, Ve-nus ,