:

Tutor. It is a term used to express the place of the heavenly body, as seen from the centre of the sun; whereas the geocentric place of a planet is the position which it has when seen from the centre of the earth."

Charles. Will you show us by a figure in what this difference consists?

place of the sun, b Venus in its orbit, a the earth in hers, and c Mars in his orbit, and the outermost circle will represent the sphere of fixed stars. Now, to a spectator on the earth a, Venus will appear among the fixed stars in the beginning of Scorpio, but, as viewed from the sun, she will be seen beyond the middle of Leo. Therefore the geocentric longitude of Venus will be in Scorpio, but her heliocentric longitude will be in Leo. Again, to a spectator at a, the planet Mars at c will appear among the fixed stars towards the end of the sign of Pisces; but, as viewed from the sun, he will be seen at the beginning of the sign Aries consequently the geocentric longitude of Mars is in Pisces; but his heliocentric longitude is then in Aries.

TUTOR. We now come to Jupiter, the largest of all the planets, which is easily known by his peculiar magnitude and brilliancy.

Charles. Is Jupiter larger than Venus?

Tutor. Though he does not appear so large, yet the magnitude of Venus bears but a very small proportion to that of Jupiter, whose diameter is 90,000 miles in length, consequently his bulk will exceed the bulk of Venus 1500 times: his distance from the sun is estimated at more than 490 millions of miles.

James. Then he is five times farther from the sun than the earth; and, consequently, as light and heat diminish in the same proportion as the squares of the distances from the illuminating body increase, the inhabitants of Jupiter enjoy but a twenty-fifth part of the light and heat of the sun that we enjoy.

Tutor. Another thing remarkable. in this planet is, that it revolves on its axis, which is perpendicular to its orbit, in 10 hours, and, in conse quence of this swift and diurnal rotation, his equatorial diameter is 6000 miles greater than his polar diameter.

Charles. Since then a variety in the seasons of a planet depends upon the inclination of the axis to its orbit, and since the axis of Jupiter has no inclination, there can be no

difference in his seasons, nor any in the length of his days and nights.

Tutor. You are right; his days and nights are always five hours each in length and at his equator, and its neighbourhood, there is perpetual summer; and an everlasting winter in the polar regions.

James. What is the length of his years?

Tutor. It is equal to, nearly 13 of ours, for he takes 11 years 314 days and 20 hours, to make a revolution round the sun, consequently he travels at the rate of more than 28,000 miles in an hour.

This noble planet is accompanied, with four satellites, which revolve about him, at different distances, and in different periodical times; the first. in about 1 day and 18 hours: the second in 3 days 13 hours: the third