earth. It has been said that if there is water there, it must be always frozen. It must also (it has likewise been said) be almost dark there, even during the day.

our moon.

Jupiter is provided with four moons or satellites, the largest of which is twice as large as These moons revolve round Jupiter in different spaces of time: the nearest goes round in about two days, and the furthest in about seventeen days. Its amount of moonlight, therefore, must be great, and much compensate, perhaps, for its distance from the sun.

Jupiter, when viewed through a telescope, has a great many singular appearances. Belts and bands, sometimes light, and sometimes dark, seem to extend across it, as represented in the following figures.

In what you see here, figures 1 and 2 repre

How many moons has Jupiter? Do they revolve round Jupiter all in the same time? How does Jupiter appear through a telescope?

sent Jupiter as viewed through an achromatic telescope, with a magnifying power of forty; and figures 3 and 4, the same planet as beheld through Sir William Herschel's great telescope, represented at another page.

Jupiter, from the largeness of its mass, is a very important member of the solar system. Through the attraction of gravitation, it disturbs or influences the motions of the earth; and even its satellites disturb what would otherwise be the motions of comets. Yet (as ascertained by the process referred to at my page 96) the mass of one of those satellites (the smallest) is sixtyfive millions of times less than the mass of the

sun.

Many astronomical truths are obtained only through observation of Jupiter and its satellites.

CHAP. XLIV.

ABOUT SATURN.

SATURN is nine hundred millions of miles from the sun, and performs its revolution in about thirty years. It turns on its axis in little more than ten hours. It is supposed to be eighty times colder upon this planet than upon the earth. Saturn is seventy-eight thousand miles in diameter; and, excepting Jupiter, it is the largest of the planets.

Saturn has seven moons or satellites, which revolve round it in different periods of time: the shortest period is one of our solar days, and the longest eighty days.

Saturn is surrounded by an immense thin

How far is Saturn from the sun?

How long is it revolving

round the sun? How long turning on its axis? Is it colder

upon Saturn than upon the earth?

Saturn? How many moons has it?

What is the diameter of

ring, or rather by two rings, one within the other, as you see in the picture. These rings

turn round the planet from west to east, and complete their revolution in ten hours. The light of the sun, falling upon them, gives them a bright appearance, even brighter than the planet itself. When viewed through a telescope, Saturn appears to have spots and belts upon its face, like Jupiter. Stars are also sometimes seen

By what is it surrounded? Do these rings revolve round Saturn? What makes them look bright? How does Saturn appear through a telescope?