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Venus.

Saturn...

..Gold....

. Silver...
.Iron.....
.Quicksilver..
.Tin...
..Copper
....Lead

..Sunday.
.Monday.
.Tuesday.
Wednesday.
.Thursday.
Friday.
...Saturday.

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We need not seek to account for the connexion of gold with the Sun, nor of silver with the Moon, when the poets of all ages and nations have celebrated "the golden sun," and "the silvery light of the moon." From iron the god of war formed the weapons of destruction; while the nimble Mercury, that slippery, light-fingered fellow, the patron of roguery throughout the ancient world, was well identified with quicksilver. The metal tin seems to have been assigned to Jupiter, from the circumstance that the Corybantes, the priests of Cybele, who tended the infancy of Jupiter in Crete, used to drown his cries by the clashing of their tin cymbals. Copper is connected with the name of Venus, who was the tutelar deity of the island of Cyprus. This place, where Venus was born, formerly sup; plied the world with copper from its mines, and honoured Venus above all deities. Lead may have been set down as the type of Saturn, in consequence of the dull, lead-like appearance of that planet.

1. The Sun has but a very small motion in the heavens which is due to the attraction of the different planets nearly all the variations which appear in his dimensions arise from the motion of the planet on which the spectator is situated, and not from the motion of the Sun. But, although the motion of the Sun in an orbit is very small, never extending beyond the length of the solar diameter, yet he has another species of motion quite independent of any change of place; we mean a motion round his axis, which is completed in twenty-five days. The means by which this motion is made manifest, are the disappearance and re-appearance of certain dark, or shaded spots, on his further on; but we may now state, that certain dark spots brilliant surface. These spots we shall have to allude to appear to travel, as it were, across the sun,-disappear at the western edge, become lost for a time to the view,re-appear at the opposite or eastern edge,-and then attain their former position. This can only occur on the supposi tion that the sun revolves on his axis; and the period of such revolution, as determined by these spots, after making allowance for the motion of the earth, is, as we have stated, about twenty-five days. It is easy to produce familiar illustration of such a motion. Suppose that we have an orange, with a dark spot on one part of its surface: if we turn the orange round on its axis, that is, in the way that reach one edge of the visible part of the orange,-pass a top spins, we shall find that the dark spot will gradually round on the remote side,-and re-appear on the opposite edge from that at which it previously disappeared.

The apparent size of a body to a spectator depends on and secondly, the distance at which it is placed from the two circumstances:-First, the real size of the object; observer. Now, as we may reasonably suppose that the sun's dimensions are constant, any variation in his appa

The days of the week were respectively connected with each planet, as each planet was said, according to the old astrological rules, to be in the ascendant for the particular day; We need bring no arguments to show that we are justified in selecting the sun as the first object of our attention:-rent size must be due to distance. It may now be asked both from the influence which his superior dimensions how we can describe in words, the size of which the Sun by one who has not previously thought of these subjects, enable him to exert on the other planets, and from the vast importance which attaches to him, as the source of light appears to us? If we say that he looks as large as an and heat to the other bodies of the solar system. orange, no definite information is conveyed to the mind by such a statement; because, if an orange be held at a few inches distance from the eye, it will appear much larger than the Sun; whereas, if it be held at some yards distance, it will appear smaller than the Sun. It is obvious, therefore, that we must devise some other mode than comparisons of this sort, if we wish to convey to others an idea of the size of an object.

THE SUN.

THIS magnificent globe is 883,210 miles in diameter, about 2,774,692 miles in circumference, and distant from the earth about ninety-five millions of miles. It will be convenient to consider this luminary under three points of view:-1st, His apparent dimensions, as influenced by distance: 2nd, The phenomena presented by him as a source of light:-3rd, The heating effect of his rays.

The mode, which is adopted for this purpose, is to express the angle, which the diameter of a body subtends, or is opposite to. As we shall frequently have to speak of

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lean the stick into the direction denoted by the dotted line DC: then the opening or space included between the stick and the table will be smaller than before. When we incline the covers of a book towards each other, in the act of closing the book, we produce a similar effect to that which we have just noticed ;-that is, we make two lines, or two surfaces (as the case may be,) close towards each other, as if one were about to lie on the other. This effect, then, is expressed, by saying that the angle D C B is smaller than the angle A CB. (We always place the letter attached to the point of junction of the two lines, between the two letters indicating the other ends of those lines.) If the stick were still more inclined, so as to occupy the position BC, then it would appear to approach still nearer to the table; the space included between them would be smaller; and we should say that the angle ECB is smaller than either of the former angles. It is observable that, in this way of considering the subject, the length of the stick, and the length of the table, have nothing whatever to do with the size of the angle; this is a constant rule whenever the size of angles is spoken of.

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that, if one line were drawn from one edge, and another from the opposite edge of the object, to the eye, those two lines would form with each other an angle of such dimen sions.

The Sun is nearer to the Earth at one part of the year than he is at another, as the Earth's orbit is oval, not circular; and the Sun is in the focus of that ellipse, or oval. When, therefore, the Earth is at that portion of her orbit which is nearest to the Sun, which takes place in our winter, the Sun must obviously appear larger to a spectator on the Earth's surface, than in the summer, when the Earth is further from the Sun: accordingly, it is found that in the middle of Winter, the Sun's diameter is about thirtytwo and a half minutes, and at Midsummer about thirtyone and a half minutes of a degree. From the apparent diameters of the sun and planets, their real diameters are easily calculated, when the distances of these bodies are once known.

As we thus acquire the means of distinguishing a large angle from a small one, we must now inquire what are the means by which two angles admit of being compared with each other. The opening which we have called a right angle, is supposed to be divided into ninety equal parts, called degrees. If the stick were so much inclined, that the opening between it and the table were only one degree, the stick would be almost lying down on the table. If the angle were two degrees, the stick would be a little more raised, and so on, until it became quite upright, when it would form a right angle, or an angle of ninety degrees, with the table. For further convenience, a degree is subdivided into sixty minutes, and a minute into sixty seconds. These divisions are known by the symbols :-thus, 25° 48′ 50′′, implies twenty-five degrees, forty-eight minutes, and fifty seconds.

The apparent dimensions of the Sun, as seen from the other planets, may be thus conveniently expressed by means of the angle, as before described. We shall, however, find it more satisfactory to present in a diagram, (fig. 9,) the comparative dimensions of the Sun, as seen from the different planets:-for instance, if a circle of half an inch in diameter be made, as in the figure below, to represent the Sun as seen from the Earth, then the diameter and apparent size of the Sun, as seen from each of the ten planets, will be as laid down in the diagram. (Fig. 9.)

2. Luminous effects of the Sun. What light is we know not! Its cheering, grateful influence, we all feel and acknowledge; but we do not know of what, nor how it is made. From the moment that the Creator made the Sun, "to rule the day," up to the present moment, this Sun has continued to shed a flood of light upon all around: and yet the store is not exhausted: nor is it diminished, so far, at least, as we can tell.

We shall now find that this mode of proceeding furnishes us with a very convenient method of describing the apparent diameter of the Sun. If a line were drawn from the eye to the top of the Sun, and another line from the eye to the lower part of the Sun, those two lines would be very nearly parallel, or one would nearly lie upon the other. But still they would not do so exactly; and the small space between them would furnish us with an angle to which we could give a value and a name. Now, it is found that two lines so situated, would form an angle of about half a degree: when, therefore, we speak of the diameter of a planet subtending an angle of so many minutes, we mean

Mercury.

The ancients believed that the Sun was a globe of fire, which constantly darted its beams upon the Earth; but modern science has elicited circumstances, which seem to show that such is not the case. If the Sun be viewed through a powerful telescope, with coloured glasses interposed, to prevent the intense light and heat of the sun from hurting the eye, it will be found that there are numerous dark spots of various forms and dimensions. Some of them are perfectly black, while others have a shaded, or partially-enlightened appearance. These spots, which were first made known to the world by Galileo, about 240 years ago, are subject to much fluctuation: sometimes they appear to expand and enlarge in their dimensions; at other times they seem to contract and become less perceptible. Sometimes they divide into a greater number, while at other times two or more appear to coalesce. Some of these spots have been supposed to be of the immense magnitude of 45,000 miles in diameter; and they have been observed to close up entirely in the space of six weeks; which renders a velocity of a thousand miles per day necessary for the approaching borders of any such spot.

Those parts of the sun's surface which are not occupied by these spots, are still far from uniform in their appearance they have in many places a mottled aspect, as if numerous pores, or small apertures, were present in the luminous surface. There are, again, other places, which are occupied with luminous vapours and lines brighter than the general surface, and which are called facule; while the dark spots mentioned before are termed maculæ.*

From

From all these circumstances it has been conjectured that the substance or body of the sun itself is really dark or non-luminous; but that he is surrounded with a luminous atmosphere: and that any diminution or removal of such atmosphere at any given point will occasion the dark appearance, which we call a macula. By some it has been * Macula is the Latin for dark spots; faculæ, little torches.

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supposed that the black spots are the summits of lofty mountains, which penetrate beyond the luminous atmosphere, and therefore present a dark appearance to the eye. To this it has been objected, that, if such were the case, the sides of the mountain would present a gradation of light, from the black spot at the summit, to the general brilliancy of the sun's surface; whereas, such is not found to be the case. The black spots are in many cases surrounded with penumbra, or partially luminous portions, terminated by distinct and well-defined edges; thereby presenting no appearance of gradation of luminosity.

All these circumstances are considered to lead, more or less directly, to the conclusion, that the Sun owes its brilliantly luminous appearance to an atmosphere which surrounds it; and this supposition is further supported by a very remarkable fact, which the progress of optical science has revealed during the present century. There is often used in experiments in Optics, a three-cornered piece of glass, called a prism, which is oblong, and which if viewed endwise, has a triangular form. When the Sun's rays pass through a piece of glass, or other transparent body of this form, the beam of light is spread out into an oblong form, and is variously coloured,-being red at one end and violet at the other;-the space between being occupied by orange, yellow, green, blue, and indigo. These are the appearances presented under general circumstances; but if this oblong coloured space (which is called the solar spectrum*) be carefully viewed with the aid of a telescope, it is found to be crossed by a large number of fine dark lines, as many, indeed, as 600 in the whole.

Now it is supposed that this is owing to the absorption, on the part of the sun's atmosphere, of some of the coloured rays of light, whereby a black line is given out at those parts of the spectrum which, had the rays in question not been absorbed, would have uniformly contained coloured

rays.

Sir William Herschel, who was for many years the Astronomer Royal, supposed that there was an elastic atmosphere surrounding the Sun, composed of a cloudy, or partially visible, stratum of air; and that above this atmosphere was a luminous or light-giving atmosphere. When, from any cause, a portion of the latter atmosphere was removed, a dimly reflected light would be seen on the surface of the cloudy stratum, and thus the faint light or penumbra, is perceived. At any rate, the central part of the sun's disct appears, notwithstanding the spots and irregular appear ances, to be the most luminous. It must, however, be acknowledged that in this, as well as in many other branches of science, we know but little of the real nature of the cause, whose effects we study. Why it is that the Sun differs from almost all other bodies of which we are cognizant in nature, in constantly giving out light without, so far as we know, receiving any light from any other source, is to us a mystery; and cannot fail to excite our admiration,dependent as we are, for so much that is beneficial to us, on that

prime cheerer, Light!
Of all material beings first, and best!
Efflux divine! Nature's resplendent robe!
Without whose vesting beauty all were wrapt
In unessential gloom; and thou, O Sun!
Soul of surrounding worlds! in whom best seen
Shines out thy Maker! may I sing of thee?

3. Heating effects of the Sun. That the Sun is the most prolific source of heat is manifested to us in the grand routine of natural operations. We may warm our apartments by kindling a fire:-we may dress our food by the application of heat, either to the food itself, or to the water in which it is immersed ;-and important and indispensable are such processes:-but, if we compare them with the phenomena of the seasons, how humble and trifling do they appear! A fire will convey warmth to but a small space around it, and to but a small number of persons; but how sublime and vivifying is the effect which that seeming "globe of liquid fire," the Sun, produces on the earth! The millions, who inhabit our globe, look to the heating power of the Sun, as the source by which their vegetable productions must arrive at that maturity which will fit them for the purposes of food. What is it which renders the lichens and mosses of the polar regions so different from the luxu

* A Latin term implying an appearance.

By the term disc is meant the face of the Sun or Moon, as seeming perfectly flat; the diameter of which is considered to be divided into twelve parts, called digits

rious plants of the tropics? It is not the nature of the soil in which they grow; nor the amount of attention which they receive from man:-but it is the extent of the sun's warmth which mainly constitutes the difference referred to. The traveller in tropical climes meets with luxuriant fruits in abundance; while the navigator of the Arctic Seas is seldom cheered, when he touches land, with the sight of vegetation. Many of our readers have probably read Captain Franklin's account of a journey across the northern part of America; when the only food of the party for a considerable period was tripe de roche, which, though disagreeable in taste, was the only vegetable production which met their view in the course of a toilsome journey.

But we need not go to such extreme cases to instance the value of the Sun's warmth. What constitutes the dif ference between our own Summer and Winter? What makes the orchard and flower-garden present so different an aspect in Spring and Summer to what they afford in Winter? The Sun's heat is the cause: not that he is present at one season, and absent altogether at the other; but that he is with us longer and under more favourable circumstances, in June than in December. This, however, will occupy our attention hereafter:-we will therefore proceed to make a few remarks on the supposed nature of the Sun's heat.

The light which emanates from the Sun is accompanied by heat in its passage to the Earth and to the other bodies of the solar system; and it is extremely probable from recent inquiries, that light and heat are not the same bodies or agencies, or whatever we may call them. We just now spoke of the passage of light through a glass prism; but we must now consider that same light as being accompanied by heat. It is found that there is more heat at that end of the spectrum which contains the red rays, than at the other end; and it has even been proved that considerable heat exists beyond the limit of the coloured rays; that is, heating rays are found where there are no luminous rays whatever:this is one of the circumstances which have given rise to the opinion, that the heating or calorific rays of the Sun are distinct from the luminous rays. The investigation of this circumstance was first set on foot by Sir W. Herschel, who, while viewing the Sun's spots through a telescope, protected his eyes by coloured glasses, and found that more heat reached his eye when some colours were employed than with others; and that some of the glasses were cracked by the influence of the heat which they absorbed more readily than those of other colours,-the difference depending on colour. Another reason why solar heat and light are thought to be distinct is, that light has been filtered, so to speak, and a brilliant focus of light presented, so devoid of heat, as to be incapable of affecting the most delicate thermometer.

The intense character of the heat evolved by the Sun may be sufficiently shown by the employment of a common burning glass; the action of which is nothing more than this:all the rays, both of light and heat, which fall on the surface of a lens, are brought into one narrow bundle, by what is called the refracting power of the glass. If, for instance, the glass be one inch in diameter, and we find the focus, which is a little bright spot or image of the Sun formed at a certain distance behind the glass, to be one-tenth of an inch in diameter, then will the light and heat be concentrated 100 times; that is the effects of a certain quantity of light and heat are assembled into a space only one hundredth part of the former space :-from this statement, however, some slight deduction will have to be made, on account of some of the rays being reflected from, and others absorbed by, the glass.

The substance of the Sun is considered to be of a weight and density corresponding to that of water; but, neverthe less, the extent of its bulk is such, that if the weight and density of the whole Earth be regarded as 1, the Sun's weight and density may be set down at 333,000.

Such are the general characteristics of the solar globe. Many other effects, produced by its means, we shall treat of in the proper place. It may be sufficient now to observe, that the action of the Sun's light and heat is the direct source of most of the processes which go on upon the Earth, whether relating to the atmosphere or to the vegetable and animal kingdoms. Pass we on now from the Sun to

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MERCURY,

whose disc Can scarce be caught by philosophic eye, Lost in the near effulgence of his blaze.

We now proceed to the consideration of the bodies which revolve round the Sun, and shall treat of them in the order of their distances, the nearest first.

We should remark, before proceeding further, that the word planet signifies a wanderer; an appellation given to those heavenly bodies, which seemed to move in circles in the heavens. Hence this distinction may refer both to the planets usually so called, and to their moons; the former of which are styled primary, the latter secondary planets. Again the primary planets are distinguished into interior or inferior; and exterior or superior :-the first pair of terms pertaining to the two planets whose orbits are between the Sun and the orbit of the Earth; the second pair referring to the planets more distant from the Sun than the Earth.

The planet nearest to the Sun, as far as we know for certain, is Mercury; which is somewhat more than 36,000,000 of miles distant therefrom, and is about 3,123 miles in diameter. He revolves on his axis in about 24 hours 5 minutes, being a little more than the time occupied by the Earth in revolving on her axis. He moves round the Sun in an elliptical orbit, (as we said do all the other planets,) and when we speak of the distance between him and the Sun, it must be understood that we refer to the mean distance. The time which he takes to travel round the Sun is almost 88 days; a period which constitutes his year; for we must bear in mind, as will be hereafter more particularly shown, that our year is nothing more than the length of time which the Earth occupies in going once round the Sun. Hence when we speak of a year as connected with the motion of Mercury, we must remember that his year is different from ours,-the latter being rather more than four times as long as the former.

As he revolves round his orbit of 72 millions of miles in diameter in about 88 days, he has a velocity of motion of about 100,000 miles an hour; a rate of which we can form some conception by considering that 100,000 miles is about four times the circumference of the earth.

As Mercury is so much nearer the Sun than the Earth, it follows that the amount of light and heat received by this planet is much greater than that received by the Earth; and it has been estimated that it is about seven times greater. Another effect of the comparative proximity of Mercury is, that he never appears so far removed from the Sun as the other planets. At no time is he more than 30° distant from

about it.

the Sun; that is, if, at any time we draw a line from the Earth to the Sun, and another from the Earth to Mercury, those two lines will never form a larger angle than 30°. It is, in part, for this reason that we do not usually speak of Mercury as a morning or an evening star; he never rises much before the Sun, nor does he set much after the Sun: and, in the next place, owing to the proximity of the Sun, by means of which the rays of this planet are, as it were, drowned, we seldom see him at any time. Not but that, in very clear weather, this planet may be seen just before sunrise in the morning, or just after sun-set in the evening, when it appears a good way off from the Sun. His appearance is brighter than that of Venus, and has a light blue tint He subtends an angle of from 5" to 12" of a degree, according to his position in respect of the Earth. There is a circumstance which satisfactorily proves that Mercury does not shine by virtue of any light of his own, but merely by light reflected from the Sun. This circumstance, which also applies to some of the other planets, is the existence of phases*, similar to those which are periodically observed in our moon. When Mercury appears at his greatest distance or elongation from the Sun, his illuminated surface has nearly the form of a half circle, more or less, according to the position of the Earth. But when he is passing round on the opposite side of the Sun to that at which the Earth is situated, the illuminated portion becomes more than a semicircle, and assumes that form which is called gibbous; which phase may be represented by placing a semicircle and a semioval with their flat edges in contact. When Mercury is at his greatest distance from the Earth, the Sun is then between them, and shuts out the view of Mercury altogether, so that the whole of the illuminated disc of Mercury can never be seen from the Earth; but when

This is a word from the Greek, and signifies appearances.

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he emerges on the other side of the Sun, he becomes again visible, and his illuminated surface approaches more and more to the form of a semicircle, as he travels on to the position in which he forms a right angle with the Sun and the Earth. As he proceeds in his orbit, he approaches nearer to the Earth, and his semicircular phase becomes diminished to a crescent, which attains its smallest dimensions, when Mercury is either exactly over, or exactly under the Sun; in which position only a few of the Sun's rays, reflected from the surface of Mercury, can reach the earth, and even those few are rendered almost imperceptible by the superior flood of light, which proceeds directly from the Sun to the Earth. These observations apply likewise to the planet Venus.

It is by such evidence as this that we know that a planet does not appear luminous by any inherent light of its own, but that we see it, in consequence of its reflecting the solar light to the Earth. There is every reason to believe that the Earth reflects light from its surface, just as we have described with respect to Mercury; and that if there be inhabitants in any of the other planets, they see the Earth under the various forms of crescent, semicircular, and gibbous. To this conclusion we arrive both by analogy, and by certain appearances of the Moon during a solar eclipse, to which we shall hereafter refer more particularly.

A line drawn from the Earth to the Sun is said to be in the plane of the ecliptic. The ecliptic may be imagined to be a large oval flat surface, which passes through the Sun, and round the edge of which the Earth moves in the space of a year. Now if we suppose a similar, but smaller, oval surface passing through the Sun, and that Mercury passes round the edge of that oval in his year of eighty-eight days, it may be asked whether these two oval surfaces coincide, or whether one slopes with respect to the other? We have to reply that they do not coincide; but that although both of them pass through the sun, they are inclined the one to the other. It will perhaps be desirable here to state that each planet may be conceived to have an oval plane belonging to itself, round the edge of which it passes in the course of its Now year; and further, that no two of these planes exactly coincide, all of them being inclined one to another. the mode of expressing the amount of the inclination, or obliquity of two such planes, is by the angle included between them. Two such planes are said to cut each other in an imaginary line passing through the Sun, which line therefore may be considered as a kind of hinge, connecting the two planes; and the angle, at which these planes are inclined to each other, is measured with reference to that line.

It will now be understood what is meant when we say that the plane of the orbit of Mercury is inclined at an angle of about seven degrees to the plane of the ecliptic, the latter term being always reserved for the plane of the Earth's orbit. If the plane of the orbit of Mercury coincided with the ecliptic, it would follow that Mercury, when at its shortest distance from the earth, would be exactly between we should therefore see him as a black spot on the central the centre of the Sun and the centre of the Earth; and that part of the Sun, which circumstance was first observed by Gassendi in the year 1631. As, however, the planes of the two orbits do not coincide, and yet the planet Mercury is occasionally seen as a black spot on the Sun's disc, the determination of the circumstance, whether or not Mercury will appear on the face of the Sun, depends on the position of the line, which joins the two planes. If Mercury happen to be at his nearest point to the Earth, when he reaches that line, then we shall see him cross the centre of the Sun's disc, in which case the line connecting the two planes will pass through the centres of the Earth, Mercury, and the Sun. But if that line be in any other direction, when Mercury a little above or a little below the centre of the Sun, or more gets between the Earth and the Sun, then he will be either From these circumstances it follows that Mercury may probably, exterior to the disc of the Sun altogether. revolve many times round the sun, without getting exactly on the line joining the Earth and the Sun. When, however, such an occurrence does take place, it is called a transit + of the planet. At such a time Mercury appears as a small He crosses the Sun's disc round black spot, because his illuminated surface is directed wholly away from the Earth. Such a transit as this occurred about the from east to west, in consequence of his motion from west by south to east. middle of the day on May 5th, 1832. These transits of the it From the Latin transitus, a passing over.

planets show that they are opaque bodies, having no light | being considered with reference to the smaller or greater of their own.

We must now explain two terms which will be frequently used in our future details; viz. conjunction and opposition. If we suppose a planet to be exactly between the Earth and the Sun, that planet is said to be in inferior conjunction with the Sun; and if the Sun be exactly between this planet and the Earth, the planet is said to be in superior conjunction with the Sun; the words inferior and superior

distance of the planet from the Earth. This, however, is not all. If the planet be either a little above, or a little below the line which joins the centres of the Earth and the Sun, it is still said to be in conjunction. We shall therefore include all the cases, if we say that a planet will be in inferior conjunction with the Sun, when such planet is the nearer of the two to the Earth; but when the Sun is the nearer of the | two, the planet will be in superior conjunction.

Fig. 10.

Conjunction

Superior Conjunction.

Inferior Conjunction.

Opposition,

The term opposition is applied to two planets, or heavenly bodies, which are so situated that one particular line, passing through both their centres, will also pass through the centre of the Earth, the Earth being between the other two bodies. This condition can never occur with respect to the planets Mercury and Venus, because their orbits being smaller than that of the Earth, the Earth can never get between them and the Sun, as may be inferred by inspecting the preceding diagram.

The conjunction of one planet with another, or with the Sun, is in most cases a favourable opportunity for distinguishing that planet in the heavens, as we are thus furnished with a clue for detecting its position. The conjunctions and oppositions, as also the risings and settings of the planets, with their precise situations in the heavens, at certain given times, are set down in a species of almanack, devoted to the furnishing of this information, day by day, whence it is called an Ephemeris. This planet, as to density of matter, is deemed to be nine times that of water, or double the density of the matter of the Earth.

It is sometimes desirable to know when a planet is towards the south, for the convenience of recognising it; but such information is of less value in the case of Mercury than of any other planet, as the proximity of Mercury to the Sun renders it seldom visible. Its time of crossing the meridian, or attaining its southern or most elevated position, varies from about a quarter past ten to three-quarters past one in the day.

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Fairest of stars, last in the train of Night,

If better thou belong not to the dawn,

Sure pledge of day, that crown'st the smiling morn

With thy bright circlet,-MILTON's Paradise Lost, b. 5.

No other planet shines with so great clearness and brilliancy upon the Earth as Venus-a circumstance due to her size, but more particularly to her nearness to the Earth. In dimensions Venus approaches much more nearly to those of the earth than any other planet, her diameter being about 7800 miles; so that if we divide the earth's diameter into sixty-six equal parts, the diameter of Venus will contain sixty-five of those parts.

Venus revolves round the Sun in an orbit, which is inclined to the Earth's orbit or ecliptic, the inclination, however, not being so great as in the case of the orbit of Mercury, this latter inclining, as we said, about seven degrees, while the former inclines less than three and a half degrees. Her mean, or medium distance, from the Sun is about sixty-nine millions of miles, nearly twice as great as that of Mercury. This mean distance gives for the circumference of her orbit about four hundred and thirty-three millions of miles, a distance which she travels over in about two hundred and twenty-five days; so that eight of her years are about equal to five of ours. The velocity with which she moves in her orbit is about seventy-five thou sand miles an hour, about three-fourths of the velocity of Mercury. Besides the motion in her orbit, she has a rotation on her own axis, which occupies about twenty-three hours and twenty minutes. This rotation is determined by carefully watching the permanent spots on the body of the planet.

The observations which we made about phases, when speaking of Mercury, apply with much more force when referred to Venus, for two reasons;-first, her illuminated surface is larger than that of Mercury,—and secondly, her distance from the Earth is subject to much greater variation than that of Mercury. At her nearest point to the Earth, she is probably about 26 millions of miles distant; but her greatest distance from the Earth is 164 millions of miles.

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