and settings of the planets, with their precise situations in the heavens, at certain given times, are set down in a species of almanac, 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.

VENUS.

With purest ray

Sweet Venus shines; and from her genial rise,
When day-light sickens, till it spring afresh,
Unrivalled reigns, the fairest lamp of Night.

We need not wonder that the poet thus hails the appearance of an object, which attracts so large a share of admiration as the planet Venus, which glitters like a gem in the dark firmament, when the Sun is lighting other parts of the Earth, and which thereby helps to break the gloom which attends upon the sable night.

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. v.

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 seven thousand eight hundred 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 thousand 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 twentythree 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 twenty-six millions of miles distant; but her greatest distance from the Earth is one hundred and sixty-four millions of miles. It is obvious, therefore, that the splendour of her light, and her apparent size, must suffer considerable modifications, as well from her varying distance, as from the phases which she exhibits. This is well illustrated in the different figures or phases of this planet, as given in fig. 12. The first phase, which is the gibbous, shows Venus, just after having passed from superior conjunction, and when at almost its greatest distance from the Earth; it not being seen when in a line with, or too close to, the Sun. The second phase corresponds to our half-moon, and is the aspect of Venus when forming a right angle with the Sun and the Earth; it is then at its greatest elongation. The third phase, or crescent, is observed just before and after the planet's inferior conjunction, and when at about its nearest distance to the Earth. Hence it has been noticed, as shown in the figure opposite, that the apparent size of Venus is indicated as greatest by the crescent form, and that her light is then most brilliant and abundant; and that her apparent size is least when in the gibbous state, and her light proportionably diminished:—all depending upon her distance from the Earth. When Venus gets near to the Earth she appears upwards of thirty times larger than when farthest off; and her light about this time is so intense as to project a real shadow upon a white ground, such as clean writing-paper. She may even be seen in the day-time, near, and soon after her greatest elongation.