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enabled to judge of the nature and end of the other systems of the universe. For, although there is an almost infinite variety in the parts of the creation, which we have opportunities of examining, yet there is a general analogy running through and connecting all the parts into one scheme, one design, one whole.
11. And then, to an attentive considerer, it will appear highly probable, that the planets of our system, together with their attendants called satellites or moons, are much of the same nature with our Earth, and destined for the like purposes. They lar planets are all solid opaque globes, capable of supporting are. animals and vegetables. Some of them are larger, some less, and some nearly of the same size of our Earth. They all circulate round the Sun, as the Earth does, in shorter or longer times, according to their respective distances from him; and have, where it would not be inconvenient, regular returns of summer and winter, spring and autumn. They have warmer and colder climates, as the various productions of our Earth require: and in such as afford a possibility of discovering it, we observe a regular motion round their axes like that of our Earth, causing an alternate return of day and night; which is necessary for labour, rest, and vegetation; and that all parts of their surfaces may be alternately exposed to the rays of the Sun.
12. Such of the planets as are farthest from the The far. Sun, and therefore enjoy least of his light, have that the Sun deficiency made up by several moons, which con- have most stantly accompany, and revolve about them; as our
enlighten Moon revolves about the Earth. The remotest their planet* has, over and above, a broad ring encom-nights. passing it; which, like a lucid zone in the heavens, reflects the Sun's light very copiously on that planet: so that if the remoter planets have the Sun's light fainter by day than our earth, they have an addition made to it morning and evening by one or more of
Saturn is now known to have two of these lucid zones or rings.
Our Moon their moons, and a greater quantity of light in the ous like the Earth. 13. On the surface of the Moon, because it is
nearer to us than any other of the celestial bodies are, we discover a nearer resemblance of our Earth. For, by the assistance of telescopes, we observe the Moon to be full of high mountains, large vallies, and deep cavities. These similarities leave us no room to doubt, that all the planets and moons in the system, are designed as commodious habitations for creatures endowed with capacities of knowing and adoring their beneficent Creator,
14. Since the fixed stars are prodigious spheres of fire like our Sun,* and at inconceivable distances from one another, as well as from us, it is reasonable to conclude, they are made for the same purposes that the Sun is; each to bestow light, heat, and vegetation on a certain number of inhabited planets;
kept by gravitation within the sphere of its activity. Number 15. What an august, whan an amazing concep
tion, if human imagination can conceive it, does this give of the works of the Creator! Thousands of thousands of suns, multiplied without end, and ranged all around us, at immense distances from each other; attended by ten thousand times ten thousand worlds, all in rapid motion, yet calm, regular, and harmonious, invariably keeping the paths prescribed them; and these worlds peopled with myriads of in. telligent beings, formed for endless progression in perfection and felicity!
16. If so much power, wisdom, goodness, and magnificence be displayed in the material creation, which is the least considerable part of the universe, how great, how wise, how good, must HE BE, who made and governs the whole!
less suns and worlds.
* Though the Sum may not, strictly speaking, be a great sphere of fire, yet it is undoubtedly the principal source of light and heat to the other bodies in the system.
A brief Description of the SOLAR SYSTÉM.
HE Sun, with the planets and comets Plate 1 17. which move round him as their centre,
Fig. I. constitute the solar system. Those planets which are near the Sun not only finish their circuits sooner, but likewise move faster in their respective orbits, The Solar than those which are more remote from him. Their
System. motions are all performed from west to east, in orbits nearly circular. Their names, distances, magni- . tudes, and periodical revolutions, are as follows:
18. The Sun o , an immense globe of fire, is The Sun, placed near the common centre, or rather in the lower* focus of the orbits of all the planets and cometst; and turns round his axis in 25 days 6 hours, as is evident by the motion of spots seen on his surface. His diameter is computed to be 763,000 Fig. 1. miles; and by the various attractions of the circum. volving planets, he is agitated by a small motion
* If the two ends of a thread be tied together, and the thread be then thrown loosely round two pins stuck in a table, and moderately stretched by the point of a black-lead pencil carried round by an even motion, and light pressure of the hand, and oval or ellipsis will be described; and the points where the pins are fixed are called the
foci or focuses of the ellipsis. The orbits of all the planets are elliptical, and the Sun is placed in or near one of the foci of each of them: and that in which he is placed, is called the lower focus.
† Astronomers are not far from the truth when they reckon the Sun's centre to be in the lower focus of all the planetary orbits. Though, strictly speaking, if we consider the focus of Mercury's orbit to be in the Sun's centre, the focus of Venus's orbit will be in the common centre of gravity of the Sun and Mercury; the focus of the Earth's orbit in the common centre of gravity of the Sun, Mercury, and Venus; the focus of the orbit of Mars in the common centre of gravity of the Sun, Mercury, Venus, and the Earth; and so of the rest. Yet the focuses of the orbits of all the planets, except Saturn, will not be sensibly removed from the centre of the Sun; nor will the focus of Saturn's orbit recede sensibly from the common centre of gravity of the Sun and Jupiter.
of the pla- gent them.
Plate I. round the centre of gravity of the system. All the
planets, as seen from him, move the same way, and
19. Having mentioned the Sun's turning round
material axes to turn upon, and support them, as The axes in the little imperfect machines contrived to repre
For the axis of a planet is an imginary nets,
line, conceived to be drawn through its centre,
when we speak of the axes of the heavenly bodies. Their or
20. Let us suppose the Earth's orbit to be a thin, not in the even, solid plane; cutting the Sun through the cen
tre, and extended out as far as the starry heavens, plane with
where it will mark the great circle called the ecliptic.
equal parts, called signs ; each sign into 30 equal
* As represented in Plate III. Fig. I. and described $ 138,
into 60 equal parts, called seconds : so that a second Plate I. is the 60th part of a minute; a minute the 60th part of a degree; and a degree the 360th part of a circle, or 30th part of a sign. The planes of the orbits of all the other planets likewise cut the Sun in halves; but, extended to the heavens, form circles different from one another, and from the ecliptic; one half of each being on the north side, and the other on the south side of it. Consequent- Their ly the orbit of each planet crosses the ecliptic in two hudes. opposite points, which are called the planets' nodes. These nodes are all in different parts of the ecliptic; and therefore, if the planetary tracks remained vi. sible in the heavens, they would in some measure resemble the different ruts of waggon wheels, crossing one another in different parts, but never going far asunder. That node, or intersection of the or. bit of any planet with the Earth's orbit, from which the planet ascends northward above the ccliptic, is called the ascending node of the planet; and the other, which is directly opposite thereto, is called its de. scending node. Saturn's ascending node* is in 21 Where sideg. 32 min. of Cancer ; Jupiter's in 8 deg. 49 tuate. min. of the same sign; Mars's in 18 deg. 22 min. of Taurus 8 ; Venus's in 14 deg. 44 min. of Gemini o ; and Mercury's in 16 deg. 2 min. of Taurus. Here we consider the Earth's orbit as the standard, and the orbits of all the other planets as oblique to it.
21. When we speak of the planets' orbits, all that the plan. is meant is, their paths through the open and unre- ets' orbits, sisting space in which they move, and are retained what. by the attractive power of the Sun, and the projectile force impressed upon them at first. Between this power and force there is so exact an adjustment, that they continue in the same tracks without any solid orbits to confine them.
* In the year 1790.