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to revolve round two fixed points, called, from this circumstance, the poles of the world, and in this motion is included the whole system of stars. The pole elevated above our horizon, is the north pole ; the opposite pole, which we imagine beneath the horizon, is the south pole. Several interesting ques. tions present themselves to be resolved: What be. comes of those stars during the day, which we have beheld in the preceding night; and from thence do those come which begin to appear? Where are those gone which have departed from our view ? An attentive examination of these phenomena will afford a simple answer to these questions. In the morning the brightness of the stars grows fainter, as the dawning-light increases ; in the evening they become more brilliant as the twilight diminishes; it is not therefore because they cease to shine, but because they are effaced by the more vivid light of the Sun, that we are unable to see them. The discovery of the telescope has enabled us to verify this explanation, by showing us the stars, even when the Sun is at its greatest elevation above the horizon : those which are néar enough the pole never to reach the horizon, appear constantly above it.. -. It becomes also an inquiry as to the number of fixed stars that we can at any one time see with the naked eye. To a common observer in a very bright · night, and in the absence of the Moon, there appears
to be an immense number, very many thousands ; but astronomers contend that, without the assistance of glasses, we cannot at one time see so many as a thousand, and that the deception is occasioned by the numberless reflections and refractions to which the light, in its passage from those stars, is subject. The heavens, however, examined by telescopes, present us with innumerable stars; the better the glasses, the greater the number that are ascertained to exist. Dr. Herschel, in a paper on the Construction of the Heavens, says it is probable that the great stratum,
called the milky way, consists of an indefinite number of stars of various magnitudes, and at different distances; and that our Sun is actually one of the heavenly bodies belonging to it. "We will,' says the doctor, retreat to our own retired station in one of the planets attending a star in the great combination with numberless others; and in order to investigate what will be the appearances from this contracted situation, let us begin with the naked eye. The stars of the first magnitude, being in all probability the nearest, will furnish us with a step to begin our scale; setting off, therefore, with the distance of Sirius or Arcturus, for instance, as unity, we will suppose that those of the second magnitude are at double, and those of the third at treble the distance, and so on. Taking it then for granted, that a star of the seventh magnitude is about seven times as far from us as one of the first, it follows that an observer, who is enclosed in a globular cluster of stars, and not far from the centre, will never be able, with the naked eye, to see to the end of it: for since, according to the above estimations, he can only extend his view about seven times the distance of Sirius, it cannot be expected that his eyes should reach the borders of a cluster which has, perhaps, not less than fifty stars in depth, every where around hiin. The whole universe, therefore, to him, will be comprised in a set of constellations richly ornamented with scattered stars of all sizes. Or if the united brightness of a neighbouring cluster of stars should, in a remarkably clear night, reach his sight, it will put on the appearance of a small, faint, nebulous cloud, not to be perceived without the greatest attention. Allowing him the use of a common telescope, he begins to suspect that all the milkiness of the bright path which surrounds the sphere, may be owing to stars. By increasing his power of vision, he becomes certain that the milky way is indeed no other than a collection of very small stars, and the nebulæ nothing but clusters of stars.'
Dr. Herschel then solves a general problem for computing the length of the visual ray; that of the telescope which he uses will reach stars 497 times the distance of Sirius. Now Sirius cannot be nearer than a hundred thousand times the length of the earth's orbit; therefore Dr. Herschel's telescope will at least reach 100,000 x 190,000,000 x 497 miles ; and he says, that, in the most crowded part of the milky way, he has had fields of view that contained no less than 588 stars, and these were continued for many minutes, so that, in a quarter of an hour, he has seen 116,000 stars pass through the field of view of a telescope of only 15' aperture : and at another time, in 41 minutes, he saw 258,000 stars pass through the field of his telescope. Every improvement in his tele. scopes has discovered stars not seen before ; so that there appears no bounds to their number, nor to the extent of the universe. "
In this month, the Sun rises to its highest part of the heavens on the 22d, but to casual observers its apparent meridian height will be the same for several days before and after the 22d. The times of the Sun's rising and setting will be as follow : Wednesday 1st, Sun rises 53 m. after 3. Sun sets 7 m. after 8 Saturday 11th . --- 46 - • ---3---- 14 • - •-8 Wednesday 22d -:-- 43-...- 3.... - 17 --•8 · The Sun will enter Cancer at 10 minutes after 3 in
the morning on the 22d. On the 1st, Venus will pass over the star marked o *, the star being 38, north of the planet's centre : and on the 16th, Jupiter will eclipse the stars s, the star being one degree south of the planet's centre.
Equation of Time. [See Explanation in January.) The following table will show what is to be subtracted from, and added to the apparent time, as exhibited by the dial, in order to set the clock or watch to equal or true time, for each 5th day of the month.
m. s. Wednesday 1st, from the time shown by the dial SUBTRACT 2 40, Monday, 6th, - - - - - - - - - - - - - 1 53 Saturday, 11th, - - - - - - - - - - . -'. O 56 Thursday, 16th, - - - - - - - - - - - - ADD O 6 Tuesday, 21st, 2 . • - - - - - - - - - 1.11 Sunday, 26th, • - - - • - - - - • - •.- 2 15,
The full Moon occurs at 15 minutes past I in the morning of the 3d day : it enters its last quarter at 27 minutes past 4 in the morning of the 11th. The change or new Moon is 32 minutes past 11 at night on the 17th, and it will enter its first quarter at 33 minutes past 4 in the afternoon of the 24ih. The time of the Moon's rising on the first four days after she is full will be as follows, viz.
June 4th, 30 min. past 9 in the evening,
5th, 21 - ... 10 - -. ditto.
7th, 39 • - - - 11 - .. ditto. The superior conjunction of Mercury will be at 12 at noon on the 6th of June. There will be but one eclipse of Jupiter's first satellite visible, of which the emersion will take place at 40 minutes past 10 in the evening of the 15th. On the 17th, at 50 minutes past 10 o'clock at night, there will be an eclipse of the second satellite. This will be the time of the emersion also ; therefore, to see this and the other eclipse, the observer must be at his stand a proper time previously,
VIEW OF THE SOLAR SYSTEM.
Of the Earth. Although we have spoken of the motions of the earth as certain, yet it may be worth while to enter a little more at large on the subject. "The motion of the earth,' says a good writer, has so long ceased to be a disputed question, that the arguments on cach side are nearly forgotten; and those who do not scruple to adopt the hypothesis of the earth's motions, are often less acquainted with the arguments on which it is supported, than they would have been in former times, when their opinions must have been the subjects of fierce contention, Of the modern writers on this topic, La Place seems to have col· lected these arguments together in the most popular and perspicuous form. Of these we shall give a cur
sory account. When we reflect on the diurnal mo- tion to which all the beavenly bodies are subject, we recognize the existence of a general cause which moves them, or which seems to move them, round the axis of the earth. If we consider that these bodies are insulated, with respect to each other, and placed at very different distances from the earth; that the Sun and the stars are at a much greater distance from it than the Moon; and that the variations in the apparent diameters of the planets indicate great alterations in their distances; and, moreover, that the comets traverse the heavens freely, and in almost all directions, it will be difficult to conceive that it is the same cause which impresses on all these bodies a common motion of rotation. But since the heavenly bodies present the same appearances to us, whether the firmament carries them round theearth, considered as immoveable, or whether the earth itself revolves in a contrary direction, it seems much more natural to admit this latter motion, and to regard that of the heavens as only apparent.
The earth is a globe, not 8000 miles in diameter; but the diameter of the Sun is nearly 100 times larger. If its centre coincided with that of the earth, its vo. lume would not only embrace the orbit of the Moon, but extend much more than as far again; from hence we may judge of its immense magnitude: besides, its distance from the earth is 95,000,000 of miles. Is it not, then, more natural to attribute to the globe that we inhabit a rotatory motion on its own axis, than to suppose in a mass so enormous, and so remote from us as the Sun is, such an extremely rapid mo