The diameter of Venus has been considered about 220 miles shorter than that of the earth. But, it appears from the measurements of Dr. Herschel, that her apparent mean diameter, reduced to the distance of the earth, is 18". 79, that of the earth being 17". 3. This result,' says Dr. Brewster, 'is rather surprising, but the observations have the appearance of accuracy.' ELEMENTS OF VENUS. Inclination of her orbit to the ecliptic, 3° 23' 32'. Mean diameter as sun from the sun, 23" 3. Place of ascending node Getnini, 15° 8′ 9′′. Retrograde motion of the nodes in 100 years, 31' 52". Place of the aphelion, 10s 9° 1' 19". Motion of the aphelion in longitude for 100 years, 1° 21' 0". Diurnal rotation, 23h. 20m. 59s. Mean distance from the sun, 68,000,000 miles. Which is the most brilliant body seen in the nocturnal heavens? When is Venus morning and when evening star? By what names is she called? How long does she appear east or west of the sun? Who first discovered that the morning and evening stars were the same? Why has Venus this character ? How must Venus appear to the inhabitants of Mercury? Were the whole enlightened side of Venus turned towards us when she is nearest the earth, how would she appear? Is Venus visible in the day time? How do shadows appear in her light? How are the light and heat of the sun at Venus compared with the same at the earth? Has Venus an atmosphere? How high did Mr Schroeter make the mountains of Venus? According to Dr. Herschel, 8,648 miles. SECTION VI. Of Mercury and Venus. Mercury and Venus are both constant attendants on the sun; in the one part of their course being the harbingers of the morning; in the other brightening the veil of evening with their setting splendor. Often seen in conjunction with the sun, but never in opposition, they form a demonstration of the truth of the Copernican system. The inferior conjunction of Mercury or Venus is, when the planet comes between the earth and the sun; or, so near the connecting line between them, as the obliquity of its orbit will admit. It is when referred to the ecliptic in the same longitude with the sun, though it may be farther north or south. The superior conjunction of either of these planets is, when the planet in that part of its orbit most distant from the earth comes into the same longitude with the sun. It is then either hidden behind the great luminary, or passes by it on the north or south. Mercury and Venus are called inferior* planets, because their orbits are nearer the sun than the orbit of the earth. When an inferior planet is at its greatest elongation, a line passing from the earth through the planet is a tangent to the planet's orbit. The greatest elongation of Mercury is 28° 20', of Venus, 47° 48'. The orbit of these planets being elliptical, the greatest elongation on one side of the sun may not be equal to that on the other side. For the position of the planets at the greatest elongation see Plate v. Fig. 1, at that part of their orbits, where they appear stationary. Mercury, like Venus, is alternately morning and evening star, though not generally thus known. Like *> Objection has been raised against the terms inferior and superior, as applied to the planets; but the terms, not improper in themselves, are sanctioned by time and the usage of the first European astronomers. Venus, being west of the sun from the inferior to the superior conjunction, it rises before him in the morning; from the superior to the inferior, east of the sun, it sets after him in the evening. The apparent motion, of the inferior planets is greatest at the conjunctions. From the greatest elongation on one side to the greatest elongation on the other, through the superior conjunction their geocentric motion is direct; through the inferior conjunction this motion is retrograde. At their greatest elongation they appear stationary in respect to the sun. A small part of the orbit nearly coinciding with the tangent line, and the eye of the observer being in that line, the motion of the planet must be either towards such observer or from him, and, of course, must be imperceptible. Let S be the sun (Plate v. Fig. 1,) E the earth, M Mercury, and V Venus. When the earth is at i, Mercury in his orbit at b appears stationary at e. While Mercury is moving from 6 through his superior conjunction at c to d, his motion appears direct among the fixed stars from e to f. At d his motion is imperceptible for a short time, when he appears stationary at f. As he passes from d through his inferior conjunction to b, his motion appears to be retrograde. At 6 he again appears stationary. The earth moves round the same focal point with Mercury, and in the same direction from west to east. But Mercury being much more swift in its motion than the earth has a relative velocity. This relative velocity only gives it the appearance of retrograde motion. The retrograde motion of Mercury in regard to the fixed stars does not commence, when the planet is at the greatest elongation east, nor does it continue till the planet is at the greatest elongation west of the For at these greatest elongations the planet will appear to move forward with the same velocity, as the sun appears to advance by the motion of earth in its sun. orbit. The stationary appearance in relation to a fixed star must be, when the geocentric westerly motion of the planet counterbalances the sun's apparent easterly motion. Venus, like Mercury, has her stationary appearance, her direct, and retrograde motion. This will appear by a slight inspection of the figure. The retrograde appearance between the earth and Mercury is reciprocal. When at the earth Mercury appears to move from d to b, the earth must seem to an inhabitant at Mercury to retrograde from h to g. Hence the superior planets, when in opposition to the sun, have the appearance of retrograde motion, as seen from the earth. The motion of all the planets, as seen from the sun, is direct. The situation and motion of the earth causes their stationary or retrograde appearance, when viewed by us. Mercury and Venus in their revolutions round the sun assume all the phases of the moon. (Plate iii. Fig. 1, 2 and 3.) We are told by Ryan, in his grammar of astronomy, that the different phases or appearances of Venus were first discovered by Galileo, in 1611, which fulfilled the prediction of Copernicus, who foretold, before the discovery of the telescope, that the phases of the inferior planets would be one day discovered to be similar to those of the moon. The accomplishment of this prediction affords some of the strongest and most convincing proofs of the truth of the Copernican system of the world that can be obtained.' One half of each of the planets is illuminated by the sun. Thus it has been uniformly said by authors. On strict examination however, it will be seen, that a fraction more than a hemisphere is illumined, the sun being a much larger body than any of the planets. The enlightened side of Mercury and Venus (Plate v. Fig. 1,) are turned from the earth at their inferior con junctions. In these conjunctions, when at or very near their nodes, they appear as dark spots passing over the sun's disk. At other times, invisible to us, they pass the sun unobserved. They appear nearly full at their superior conjunctions; but never completely so, as their enlightened side is never turned directly towards us, except at the nodes, when they are hidden behind the body of the sun. In what respect are Mercury and Venus similar? When is the superior conjunction of these planets? When the inferior conjunction? When does the motion of these planets appear direct? And when retrograde? When do they appear stationary? How is the motion of all the planets as seen from the sun? Who foretold that Mercury and Venus would assume the phases of the moon? Who first discovered the different phases of Mercury and Venus? What part of each planet is illuminated by the sun? SECTION VII. Of the Earth. Next to Venus in the solar system is the Earth. This is the planet by far the most worthy of our attention; though astronomy forbids us fully to adopt the language of the poet; Through worlds unnumbered though the God be known, 'Tis ours to trace him only in our own.' The earth affords sustenance to innumerable animated beings, which people its surface. (It is our habitation in life, and kindly covers our remains, when the parting spirit has taken its flight. In its peaceful bosom our dust must slumber, till called forth by the voice of the archangel and the trump of God.' The earth is spherical in its form. It is, not, however, a complete globe. Elevated at the equator and flattened at the poles, its form is an oblate spheroid; resembling in some degree the well-known English turnip. Of the rotundity of the earth any person may satisfy himself. The clouds at a distance appear to rise from |