a telescope, in different positions, with respect to the sun, he seems to have the variety of appearances, or Phases, as they are called, the same as we observe in the moon; only that he never appears quite round or full; because when his enlightened side is turned directly towards us, we cannot perceive him.

WILLIAM.

But why cannot we see him then?

MOTHER.

I dare say Elizabeth can answer that question.

ELIZABETH.

The planets do not shine by any light of their own, but by means of a borrowed or reflected light, from the sun, and never can be so brilliant as the sun himself; so that a planet is lost in his superior brightness, and ceases to be visible when it is very near the sun.

MOTHER,

Mercury sometimes passes between the sun and the earth, and is then seen, like a black spot, crossing the sun's Disc or face; at such times the

dark side of the planet is turned towards us, and astronomers are able to make the best observations upon him. This apparent passage of a planet over the sun is called a Transit.

Venus, which is to us the brightest, and consequently seems to be the largest of all the planets, is the next in order beyond Mercury. The length of her year, or the time she takes to go round the sun, is about two hundred and twenty-four days and seventeen hours; and the length of her day, or the time she requires to revolve upon her axis, is twenty-three hours, twenty-one minutes, and seven seconds.

The orbit of Venus is larger than that of Mercury, and her greatest elongation, or apparent distance from the sun, as seen from the earth, is nearly twice as much as his. Like Mercury, she is visible for only three or four hours in the evening, or in the morning, as she happens to be on one side or the other of the sun. When the decline of the sun's light in the evening allows her to be visible, she appears in the west after sunset, and is called the Evening Star, Vesper, or Hesperus, from her situation being westerly; and when she appears before sunrise in the east, she is called the Morning Star, Lucifer, or Phosphorus.

ELIZABETH.

Then it is Venus that Milton speaks of when he

mentions Hesperus :

Hesperus, that led

The starry host, rode brightest, till the moon
Rising in clouded majesty, at length,
Apparent queen, unveil'd her peerless light,
And o'er the dark her silver mantle threw."

MOTHER.

The light of Venus is of a white colour, and is so strong that she sometimes, it is said, casts a tolerably distinct shadow. When she is seen through a good telescope, she seems, according to her situation with respect to the sun, to have all the different shapes and appearances of the moon. I have before told you that these appearances of the moon, or of a planet, are called by astronomers its Phases.

ELIZABETH.

Is there not sometimes a transit of Venus, as well as of Mercury over the sun?

MOTHER.

There is, but very rarely; though there have been two within the last century; one on the sixth

of June, 1761, in the morning, and another on the third of June, 1769, in the evening.

The planet that comes next to Venus, is the Earth which we inhabit. Its diameter is nearly eight thousand miles, and its distance from the sun, ninety-five millions one hundred and seventythree thousand miles. It goes round the sun in three hundred and sixty-five days, five hours, and forty-nine minutes; travelling at the rate of fiftyeight thousand miles every hour, which is about a hundred and twenty times swifter than a cannon ball, though but little more than half as quick as the motion of Mercury in his orbit.

The Earth revolves on its axis, from west to east, in the course of twenty-four hours; and it is this motion that makes the sun, and all the other heavenly bodies, appear to move round us in a contrary direction, from east to west, in the same time, and is the cause of what we call, their rising and setting, and of our day and night. The orbit in which the Earth moves round the sun is distinguished from the orbits of the other planets by being called the Ecliptic.

The orbits of Mercury and Venus, being much smaller, are included within that of the Earth, and from their situation they are called Inferior Planets, while all the others, beyond the orbit of

the Earth, are called Superior, their orbits being larger than ours. The superior planets exhibit several appearances very different from those of Mercury and Venus, and of course never appear to us to pass over the sun's disc.

Mars is the first planet beyond the orbit of the earth. His diurnal rotation on his axis is performed in twenty-four hours and forty minutes. He moves round the sun at the rate of fifty-five miles an hour, in six hundred and eighty-six days and twenty-three hours of our time, which period is the length of his year, and contains about six hundred and sixty-seven of his own days; every day and night together being forty minutes longer than with us. His diameter is about four thousand four hundred and forty-four miles; and his distance from the sun about a hundred and fortyfive millions of miles. Mars, as he appears to us, is of a dusky red colour, and the least brilliant of all the planets; and his light is never so clear as that of Venus, though he sometimes appears to be nearly as large. To the inhabitants of Mars, Mercury must be very seldom visible, except at the time of a transit; and Venus will appear to them to be about the same distance from the sun, as Mercury does to us.