Page:Cyclopaedia, Chambers - Volume 1.djvu/630

 EAR

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EAR

Pbilofotk. tells us, that 'Philolaus difcover'd its Annual Motion round the Sun. About 100 Years aftet -JPhilolaus, Ariftarchus the Samian, propofld the Motion of the Earth in iirongcr and clearer Terms, as we are allured by Ar- chimedes, in Arenar,

But the Religious Opinions of the Heathen World, pre- vented the Doftrine's becoming more cultivated. For Ari- ftarchus, being accufed of Sacrilege by Cleanthes for moving Vefta, and the tutelary Deities of the Univerfe out of their Place ; the Philofophers began to lay afide fo perilous a Pofition.

Many Ages afterwards, Nic. Cufanus revived the ancient Syftem, in his Dofi. de <Pignorant. ; and afferted the Mo- tion of the Earth : But the 'Dogma got but little Ground till the Time of Copernicus, who Ihew'd its great Ufe and Advantages in Aflronomy ; and who had, immediately, all the Philofophers and Ailronomers, that durft think dif- ferently from the Croud, and were not afraid of Eccle- fiaftical Cenfures, on his Side. So that Kepler, his Con- temporary, made no Scruple to cry -. Hoderno tempore frteftmmfftmi quiatie <Pbilofophorum iS Aftronomorum Copemico adftipulantur : fietta eft htec Glades ; iiincimus fuffrttgiis melioribus : Ceteris pene fola obfiat Superftitio aut Metus a Cleanthibus.

The Arguments alledg'd againft the Motion of the Earth, are vain and frivolous. The Principal are,

i. That it is a heavy Body, and very unfit for Motion.

2. That if the Earth were to move round its Axis in 24 Hours, all our Houfes, Buildings, SSc. would tumble down.

3. That Bodies wou'd not fall upon the Places perpendi- cularly under them : Nor a Bullet, e. gr. fhot perpendi- cularly from the Ground, fall back again upon the fame Spot.

4. That it is contrary to the Words of Scripture : And,

5. That it is repugnant to our Senfes, which reprefent the Earth at Reft, and the Sun in Motion.

The Arguments for the Motion of the Earth are of ano- ther Kind, and carry otherguife Evidence with them ; being deduced from actual Obfervation and Phenomena, and not from the fanciful Surmifes of timorous Zealots. They are thefe :

1. The Sun will equally appear in Motion, and the Earth, as Handing ftill, to a Spectator on the Earth ; whether the Sun really move round the Earth at Reft; or the Earth move round the Sun at Reft.

For fuppofe the Earth in T, (Xab. Aftronom. Fig. 14.) and the Sun in 1 ; the Sun will, then appear in ov. And fuppofe the Sun to proceed in an Orbit, furrounding the Earth, from 1 to 2, he will then appear in otr ; and if he proceed further to 3, he will be feen in on: ; and thus will he appear to go on, according to the Order of the Signs in the Ecliptic.

Suppofc again the Earth in 1 ; (Fig- 15O the Sun, S, will be feen in V : Let the Earth go on from 1 to 2, the Sun will appear to the Inhabitants of the Earth to have proceeded from T to if ; and if the Earth proceed to 3, the Sun will appear to have advanced further from kioi; and fo on, according to the Succeffions of the Sign of the Ecliptic.

Thus does the Sun appear alike to move, whether it really move, or ftand ftill ; fo that the Objection from Senfe is of no Force. See Vision. But again,

2. If one of the Planets be fuppofed to have moved a certain Space, from Weft to Eaft ; the Sun, Earth, and other Planets, together with the fixed Stars, will all feem to an Inhabitant of that Planet, to have moved juft fo far round it the contrary Way.

For fuppofe a Star M, (Fig- i<f.) in the Zenith of an Inhabitant of a Planet plac'd in T ; and fuppofe the Planet to have revolved on its Axis from Weft to Eaft ; in a cer- tain Space of Time, the Sun S, will have arrived at the Zenith of T ; then the Star I, then N, then the Earth L, and at length the Star M again. To the Inhabitant of the Planet therefore, the Sun S, with the Earth L, and the Stars I, N, M, &c. will appear to have moved round the Planet a contrary Way.

Thus, to the Inhabitants of the Planets, if any fuch there be, the Mundane Sphere, with the Sun, Stars, and all the other Planets, will, as to us, appear to move round them from Eaft to Weft, And accordingly, the Inhabitants of our Planet the Earth, are only liable to the fame de- lufive Appearances with thofe of the reft.

3. The Orbits of all the Planets include the Sun, as the common Centre of them all : But 'tis only the Orbits of the fuperiour Planets that include the Earth, which how- ever is not in the Centre of any of them, as we have already fliewn under the Articles, Sun and Planet.

4. The Earth's Orbit being proved to be between thofe of Venus and Mars ; it follows, that the Earth muff turn round the Sun .- for, as it lies within the Orbits of the fuperiour Planets, their Motions would indeed appear un- equal and irregular; but they would never either be tlationary or retrograde. See Station and Retrogr ad ation.

5. From the Orbits and Periods of the feveral Planets about the Sun; and of the Moon and the Satellites round the Earth, Jupiter and Saturn ; it is evident, that the Taw of Gravitation is the fame towards the Earth, Ju- piter and Saturn, as towards the Sun ; and the periodical Times of the feveral Bodies moving around each, are in the ikmcRatio to their feveral Diftances from them. See Period.

Now, it is certain, that on the Hypothefis of the Earth's annual Motion, her periodical Time exactly fuits this Law, bearing fuch a Proportion between thole of Mars and Venus, as the feveral other Bodies directed by the fame Law do bear, i. e. the Squares of the Periods are in all, as the Cubes of the Diftances from the Centre of their Orbits. But fuppofing the Earth to be at Reft, this Law is broke moft exorbitantly.

For if the Earth don't move round the Sun, the Sun muft move with the Moon round the Earth : Now the Diftance of the Sun to that of the Moon, being as 10000 to 46 ; and the Moon's Period being lefs than 28 Days, the Sun's Period ihould be found no lefs than 242 Years, whereas in Fact it is but one Year. Which fingle Confide- ration, Mr. VVhifton thinks of Weight enough ro determine the Controverfy between the two S) Items, and to eftablilh the Motion of the Earth for ever. See Revolution.

Whereas, fuppofing our Earth to have once revolved about the Sun in a circular Orbit, whofe femi-diameter were equal to the Earth's original Diftance from the Sun fix Degrees pail its Perihelion, the annual Period would be found exactly and furprizingly equal to the Lunar or the ancient Solar Year, which were exactly commenfurate 5 containing 12 Synodical, or 13 Periodical Months, i. e. 355 Days, 4 Hours, 19 Minutes. Sec Month.

6. The Diftances of certain of the fix'd Stars from the Zenith, have been obferved to be various at various Times of the Year. That, particularly, of the 'Pole-ftar from the Pole, has been difcover'd by Mr. Flamftsad from repeated Observations, for 7 Years fucceflively ; to be greater about: the Summer Solftice, than about the Winter, by about 40 Seconds. Whence it appears, that the Earth changes its Situation ; receding from the Pole-Star, and returning back to it again Annually. See Parallax of the Earth's Orbit.

Which Argument is iurther confirm'd from this, that the Earth is nearer the Sun at Chriftmas, than at Midftummer$ as appears both from its apparent Diameter being greater in December than in June ; and from its Motion being fwifter by one 25 th Part in the former Seafon, than the latter : Whence it is thac there are about 8 Days more in the Summer half Year, viz. from March to September, than in the Winter, from September to March. See Solstice and Ecmjinox.

7. Either the heavenly Bodies revolve round the Earth in 24 Hours, or the Earth revolves round its Axis in that Time. Now the Planets, revolving round the Sun, perform their Revolutions in greater or lei's Times, as their Orbits are greater or lefs, i. e. as they are more or lefs remote from the Sun. Of Confequence, if the Stars and Planets revolved round the Earth, they would perform their Revo- lutions in unequal Times, according as their Orbits, or their Diftances, were unequally big. At leaft, the fix'd Stars, which are at inch prodigious Diftances from the Earth, wou'd never move round it in 24 Hours, as the neareft Planet is fuppofed to do. See Revolution.

This is an Inelegancy, which is avoided in the Syftem where the Earth is fuppofed to move ; and where every Planet is fo much the longer in defcribing its annual Orbit round the Sun, as the Orbit is greater. See Orbit.

8. In all the Works of Nature we are acquainted withal, the Creator appears to afl by the fhorteft, cafieft, and fimpleit Means. Now, if the Earth be at Reft, and the Stars move, the Velocity of thefe latter muft be immenfe, and yet all the Purpofes thereof, might have been anfwer'd by a moderate Motion of the Earth alone.

For the Moon's mean Diftance from the Earth, is 57 Semi-diameters of the Earth ; which, fuppofing a Semi- diameter of the Earth 3440 Geographical Miles^ amounts to 196080 Miles. Hence, the Circumference of the Moon's diurnal Circle, being 1231380 fuch Miles, the Moon's horary Motion muft be 483308 Miles: Confequently in each Se- cond, a Space lefs than that of the Pulle of an Artery, the Moon, tho' the iloweft of all the heavenly Bodies, muft move 3 Miles and five 9 ths. See Moon. Again, the Sun's mean Di- ftance from the Earth is 22000 Semi-diameters of the Earth, or 75<SSoooo Geographical Miles; confequently the Sun's diurnal Progrefs, when in the Equator, muft be 475270400 Miles : And therefore in the Space of one Second, i. e. in the twinkling of an Eye, he muft move 5480 Miles.

Again, the Diftance of the Sun .from the Earth, is to that of Mars nearly as one and a half; to that of Jupiter, as one to five and a Quarter ; and to that of Saturn, as one to nine : Wherefore as the diurnal Spaces, and all other Things defcribed in the fame Time, are in the fame Ratio ; Mars, in

one