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per objects near enough to be benefited by their They are influence. Whoever imagines that they were created surround. only to give a faint glimmering light to the inhaed by pla- bitants of this globe, must have a very superficial
knowledge of astronomy, and a mean opinion of the
9. Instead then of one Sun and one world only in the universe, as the unskilful in astronomy imagine, that science discovers to us such an inconceivable number of suns, systems, and worlds, dispersed through boundless space, that if our Sun, with all the planets, moons, and comets, belonging to it, were annihilated, they would be no more missed, by an eye that could take in the whole creation, than a grain of sand from the sea-shorethe space they possess being comparatively so small, that it would scarce be a sensible blank in the universe. Saturn, indeed, the outermost of our planets, revolves about the Sun in an orbit of 4884 mil. lions of miles in circumference ;* and some of our comets make excursions upwards of ten thousand millions of miles beyond Saturn's orbit; and yet, at that amazing distance, they are incomparably nearer to the Sun than to any of the stars. This is evident from their keeping clear of the attractive power of all the stars, and returning periòdically by
virtue of the Sun's attraction.
vided with accommodations for rational inhabit-
The Georgian planet, discovered since Mr. Ferguson's time, revolves round the Sun in an orbit 5673 millions of miles in circumfer
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 har 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.
thest from Sun, and therefore enjoy least of his light, have that 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.
ous like night-time.
Our Moon their moons, and a greater quantity of light in the
14. Since the fixed stars are prodigious spheres
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
16. If so much power, wisdom, goodness, and
less suns and worlds.
* Though the Sun 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.
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 repreof the pla
sent them. For the axis of a planet is an imginary
about which it revolves as if on a real axis. The
when we speak of the axes of the heavenly bodies. Their or
20. Let us suppose the Earth's orbit to be a thin
equal parts, called signs ; each sign into 30 equal
* As represented in Plate III. Fig. 1. and described S 138.