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THE MOON, AS SEEN THROUGH A TELESCOPE.

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260. The Moon always keeps the same side towards the Earth, so that she turns once on her axis as she moves round the Earth; and her day and night are, consequently, as long as the period from new moon to full moon. But the Earth acts also as a moon to her, being at the same time far more luminous; so when it is new moon to the Earth, it is a full earth to the Moon, and the contrary.

261. As the Moon shines with no light besides that which she reflects from the Sun; it is evident, that her shape must depend on her position in regard to the Sun and Earth.

When the Earth is exactly in the middle, the whole illumined side of the Moon will be towards the Earth, and it will be a full moon.

When the Moon is in the middle, her dark side will be presented to the Earth; and it will be new

or no moon.

As she proceeds from new to full, more and more of her light side will appear, or it will in

crease; and on going from full to new, it will, of

course, decrease.

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S is the Sun; T the Earth; the inner circle represents the Moon in its orbit receiving its light from the Sun. The outer circle is the portrait of the Moon in each adjoining part of her orbit as seen at the Earth. Thus at

A it is full moon, or all light, as at a; and at E it is new, or all dark, as at e. At E it is in a position to produce an eclipse of the Sun, or overshadow the Earth; and at A to be eclipsed itself, or receive the Earth's shadow.

262. As both Earth and Moon cast long shadows, it is evident, if they be moved on the same level, that every time the Earth passes between the Sun and Moon, the Earth's shadow would fall on it, and darken or eclipse the Moon; and

that every time the Moon passes between the Sun and Earth, the Moon's shadow would eclipse the Sun.

263. The Moon, however, ascends and descends 5 degrees in every revolution, so that in general the shadows pass under or over; but when the new or full moon take place at the very time she is passing the plane of the Earth's orbit, in ascending or descending, then the striking phenomena of an eclipse take place.

264. The shadow of the Earth, as seen on the Moon, demonstrates its rotundity; and the shadow of the Moon on the Earth, proves that it is nearer than the Sun; so the passing of the Moon over planets and stars, called Occultations, proves that they are more distant than the Moon.

265. Occasionally, Venus and Mercury, the two planets nearer to the Sun than the Earth, pass over the surface of the Sun like black spots, called transits of Venus and Mercury.

This proves that those planets are nearer to the Earth than the Sun; and, by observing the progress of the transit at different parts of the Earth, we can obtain the measure of an angle, by which we can determine the exact distance of the Earth from the Sun.

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266. Having ascertained, by means of the observation of a transit, the distance of the Earth from the Sun, the distances of all the other planets are determined by that law of nature, which exactly proportions the cubes of the distances of the planets, to the squares of their respective periodical revolutions. That law, was discovered

by the celebrated Kepler, in the beginning of the seventeenth century.

267. Besides affording us light, the Moon affects the waters, and causes high tides; which obey her influence, as the seas pass beneath her. But as she moves forward in her orbit 12 or 13 degrees every day, and consequently passes over every sea 50 minutes later one day than the day before, so the time of high water is always 50 minutes later each following day.

Obs. 1.-There are two tides in every twenty-four hours; and one is evidently but a returning vibration, stroke, or effect of the preceding tide. If the Moon were to be destroyed, and not to re-produce the effect on the following day, the vibration of the waters would probably continue for many days, till it gradually ceased, like the motion of a pendulum. Many mathematicians have puzzled themselves in calculating the relative forces acting on the near surface, centre, and remote surface of the earth, but to little purpose, as the effect is so much bet ter accounted for by the vibratory property of fluid bodies.

2.-Sir Richard Phillips, in a late Essay in the Monthly Magazine for September and October, 1811, successfully combated the prevailing notion of an occult or invisible influence called attraction, acting between the planetary bodies by means of supposed effluvia. He proves, on the contrary, that all the phenomena of the planetary motions are produced by the universal pressure of an elastic medium, on all masses of matter; the interception of which pressure, by the different masses in regard to one another, produces their mutual gravitation towards one another. Their circular and rotary motions, he ascribes to the action of their fluid parts; and thence, he explains the courses and uses of the tides of the sea.

268. The Sun and moon concur in raising the tides and hence, we have high or spring tides,

when their actions concur at the new and full moon; and low or neap tides, when the forces act in opposite directions, as at the quarters; or when the Moon is half way between the conjunction and opposition.

Obs.-On small seas not readily communicating with others, and on which the rotary forces act generally, there are no tides.

269. All the terrestrial phenomena, and all the problems on the globes and maps, may be reduced to one general principle; that the Sun always illuminates one half the earth, and that the other half is in darkness; and that, from every part of the earth, we always see one half the heavens, the other half being invisible.

270. The circumference of the earth, the heavens, and of all circles of the earth and heavens, is supposed to be 360 parts or degrees; consequently, half a circle, or half the heavens, is 180 degrees, and a fourth 90 degrees. On the surface of the Earth, each degree is 69 miles; but the actual size of a degree, as carried out to the heavens, is indefinite.

271. Hence, if the Sun illumines half the Earth, he illumines 180 degrees of the Earth; or 90 degrees every way, from the place over which he is vertical. Hence also, it is 180 degrees from the north to the south pole; and 90 degrees from each pole, is the middle of the Earth called the Equa

tor.

272. Hence, as half the heavens are always visible, 180 degrees are visible, and from the point over head, it will be 90 degrees to that line, where the earth and the heavens appear to the eye to

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