ASTRONOMY.

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reclly under them on the earth, viz. pz cs, pj and p u s ; cir-cles drawn from the zenith perpendicular to the horizon are de-nominated vertical or azimuth circles. The diurnal motion ofthe celestial bodies are rationally accounted for by the revolutionof the earth on its axis p s, and the annual motion of the sun bythat of the earth’s motion in its orbit. By means of these circlesand divisions of the sphere astronomers easily ascertain the placesand relative positions of any points or bodies in the heavens; theparticulars here mentioned will be further illucidated as we proceed.

Sect. II. Or the principal Systems of Astronomy.

(45.) To account for the celestial phenomena various hypo-theses have been formed, by each of which some of these pheno-mena may bo explained, yet none of them, except the Coper-rucau system, agree throughout with the appearance of the hea-vens. According to the Egyptian system, the earth is immove-able in the centre, about which revolve, in order, the Moon ,Sun, Mars, Jupiter, and Saturn; and about the Sun revolve Mer-cury and Venus . See Plate XX. Fig. 1.

(45.) The Ptolemaic system supposed the earth to be perfect-ly at rest, and the sun, moon, planets, comets, and fixed stars, torevolve about it every day; and that besides this diurnal mo-tion, the sun, moon, planets, and comets, had a particular mo-tion in respect to the lixed stars, and to account for their retro-grade motions and stationary appearances they were supposed torevolve in epicycloids, lly supposing a multitude of unnaturalmotions in the heavenly bodies, this system explicates the appa-rent motions ; but cannot by auv means solve the phases of Mer-cury and Venus , together with other phenomena, and thereforecannot he taue. Above the firmament of fixed stars Ptolemy places two spheres called the lirst and second crystalline heavens,over which is the Primum Mobile to give motion bv some unac-countable means to the whole machine. See Plate XX. Fig. 2.

(47.) The Tychonic system, (Plate XX. fig. 3,) was invented byTycho Brahe , who supposed the earth absolutely at rest, and thatthe sun and moon revolved about the earth ; the moon in amonth, and the sun in a year ; and at the same time, that the restof the planets, Mercury', Venus, Mars, Jupiter, and Saturn , re-volved round the sun ; the three last also encompassing the earth.Besides these motions, he supposed them all to have a diurnalmotion round the earth, as well as all the comets and fixed stars.

(48.) The Semi-Tychonic system supposed the planets to re-volve round the sun, while the sun and moon revolve about theearth as their centre of motion ; and it supposed the earth to moveabout its axis from west to east in 24 horn's. 'Phis svst m differsfrom the Tychonic only in this, that it supposes a diurnal motionin the earth, but, like the Tychonic , denies an annual one.

(49.) The Cartesian system, (Plate XIX. fig. 14,) so namedfrom its author Des Cartes , supposes a variety pf vortices orwhirlpools, in which the motions of the heavenly' bodies are per-formed, being carried round the sun in a vortex of ethereal mat-ter, in different limes, proportioned to their distances; and eachplanet having also a particular vortex of its ow n, in which themotions of its satellites are performed. From the laws of motionit will easily appear, that the irregular motions of the planets can-not be accounted for by these vortices; and besides, the suppo-sition of an ethereal matter, to perform the operations, is withoutany foundation, or analogy in nature.

(50). 'File system now universally received is called the Coper-nican. It was maintained by Pythagoras and his disciples about B. C.500: It entirely gave way to the Ptolemaic, but was revived by Co-pernicus. Here the Sun is placed in the centre of the system, andthe planets move round him in the following order : Mercury ( $ ),Venus ($?), the Earth (®),Mars (J 1 ), Ceres Kerdinandea, Pallas,Juno, Vesta, Jupiter (If), Saturn (Jy), and the Gcorgium Sidus($). The Earth, Jupiter, Saturn , and the Hersciiel, or theGeorgium Sidus, are accompanied throughout their orbits bytheir respective moons, which constantly revolve about theirprimaries. The comets move also round the sun in very eccen-tric orbits, but the lixed stars are considered as stationarybodies at immense distances from the planetary regions, and fromone another. See Plate XXI. ’Flic apparent diurnal revolutionof the whole heavens is accounted for by the earth turning on itsaxis in 23 hours 56^ minutes. This is a most complete systemof astronomy capable of solving every phenomenon in a satisfac-tory manner: every new appearance and discovery tends move and

more to confirm it. Sir Isaac Newton hath fully established thetruth of this system in his “ Principal.”, This system is represent-ed in Plate XXI. the orbits of the planets being marked in orderfrom the sun. '1 he four last discovered planets have their orbitsrepresented by dotted lines which could not conveniently be putin their due proportions. The orbits are not all in the same plane ;in the figure the black part of the orbit is that which lies below orsouth of the ecliptic, the other part is above it; lienee the points ofintersection or nodes are represented.

(51.) It may be proper here to enumerate a few of the pheno-mena which evince the truth of what is here aborted. HereVenus and Mercury from their inferior to their superior conjunc-tion, appear, first horned, then dichotomised, and next gibbous,and the contrary from the superior to the inferior conjunction.They are. always retrograde in the inferior, and direct in the supe-rior conjunction, and stationary nearly at their greatest elongation.Mars and Jupiter appear gibbous about their quadratures; but inSaturn and the Uerschel this is not sensible on account of theirgreat distances. The motions of the superior planets are direct intheir conjunction, and retrograde in their opposition ; Mercury andVenus , in their lower conjunctions are sometimes observed to passlike a dark spot over the sun’s disk, and in their upper conjoin -tions are sometimes hid behind the sun ; their apparent magni-tudes are lead at the superior, and greatest at the inferior conjunc-tion. Mercury’s greatest elongation is 28° 20', and that of Venus 47° 48'. 'Fhe apparent magnitudes of the superior planets is leadat their conjunctions, and greatest at their oppositions." All the: eknown phenomena, and many others, are such as ought to takeplace in the Copernican system. The motions of the planets arealso such as ought to take place on physical principles, for it is physi-cally impossible for a large body to revolve about a small one.See Attraction and Central Forces. If the earth were atrest, it would, from the nature of gravitation, become a perfectglobe, and were it to revolve on an axis, the form would be anoblate spheroid ; but the true figure of the earth is that of an ob-late spheroid, being most elevated under the celestial equator ;therefore the earth revolves on its axis, which causes the apparentrevolution of all the heavenly bodies. The harmony of thewhole, and the natural manner in which every phenomenon is ex-plicated, clearly demonstrate the truth of this system, which weshall therefore receive as the true system of the world. But it hasbeen objected against the Copernican system, that there are pas-sages in Scripture which assert the immobility of the earth, and (hemotion of the sun and heavenly bodies. The texts that are pro-duced on this occasion are the following: Gen. xv. 17. “ V henthe sun went down, and it was dark, behold, a smoking furnace,”&c. Gen xix. 23. “ 'Fhe sun was risen upon the earth, when Lotentered into Zoar.” Josh. x. 12, 13. “ Sun , stand thou stillupon Gibeon , and, thou, moon, in the valley of Ajalon. Andthe sun stood still, and the moon staved, until the people hadavenged themselves upon their enemies. Is not this written in thebook ot Jaslier? So the sun stood still in the midst of heaven, andhasted not to go down about a whole day.” 2 Kings xx. 11,“ And Isaiah the prophet cried unto the Lord, and he brought theshadow ten degrees backward, by which it had gone down in thedial of Ahaz .” 1 Chron. xvi. 30. " 'Fhe world also shall be sta-ble, that it be not moved.” Psalms xciii. 1. “ 'Fhe world also isstablished, that it cannot be moved.” Psalms civ. 5. God is saidto lay “ the foundations of the earth, that it should not he removedfor ever.” Eeeles. i. 4, 5. “ One generation passeth away, andanother generation cometh; hut the earth abided) for ever. Thesun also ariseth, and the sun goeth down, and hasteth to the placewhere he arose,” &c. &c. The above arc the principal portionsof scripture, that are urged against the motion of the earth ; allwhich are thus ably answered, in a general way, bv Ur. Del'll; min his Astro-Theologv, pages xx, xxi. “ The design of the holywritings, (says lie,) F not to instruct men in philosophical, hut di-vine matters, therefore it is not necessary to restrain the sense ofthose texts to,the strict propriety of the words, but take them tobe spoken according to the appearance of things and the vulgarnotions and opinions which men haVe of them, not according totheir reality, or philosophical verity. Thus in divers other in-stances the Holy Scriptures speak, and thus even philosophersthemselves speak. A ea, the Copernicans themselves, althoughthey professedly own and defend the contrary; yet in vulgarspeaking in our present case, say, Tie sun riseth, setteth, and