cond, in little more than eight days and a half; the third, in nearly eleven days; the fourth, in about thirteen days and a half; the fifth, in thirtyeight days and about two hours; and the sixth, in nearly a hundred and eight days. It is a remarkable circumstance, that the motion of all these satellites is retrograde; that is, they turn in a direction contrary to that in which their primary planet moves in its orbit. In all probability, Herschel is attended by more satellites, than those already discovered; but owing to their small size and his great distance, they may be invisible to us, even with the assistance of the best telescopes. WILLIAM. You have not told us of any moons belonging to Mars. Are there none to give light in the night to his inhabitants ? ELIZABETH. Mars is himself so small, that if he had satellites they would, it is most likely, be too small to be seen by us. MOTHER. True he is only one-fifth part as large as the : earth, so that his satellites must be very small indeed; and none have, in fact, been yet discovered. But to his inhabitants, the earth and our moon must have the appearance of two moons, a greater and a less; so that they are not obliged to pass their nights in total darkness; even supposing Mars not to have any moons of his own, which we cannot be certain is the case. WILLIAM. What reason is there for supposing that any of the planets besides the earth are inhabited? No one can ever have seen the people that live on them. MOTHER. From the observations made by astronomers, on the planets and their attending moons or satellites, we learn that they are probably of much the same nature as the globe we inhabit. It is true, they vary in size, and in the time they take to perform their revolutions round the sun; but in such of them as can be accurately observed, a regular revolution round their axis, like that of our earth, has been discovered, which causes every part of their surface to be exposed to the light and heat of the sun, and produces the regular and alternate return of day and night. ELIZABETH. Besides, as mountains and vallies have been seen in the moon, which is the planet nearest to us, we may suppose that they exist in the others, and that their effects are probably the same; and that it is only their great distance from us that prevents our perceiving them : "Her spots thou seest As clouds, and clouds may rain, and rain produce Allotted there." MOTHER. And when we consider, how very small our earth is, in comparison with several of the other planets, which all appear to be blessed with the same advantages that we enjoy, it is not unreasonable to conjecture, that instead of being placed in the heavens merely to be gazed at by us, and to reflect to us a little of the sun's light, they are filled with beings as capable as we are of feeling gratitude to their Creator. I WAS going to propose that we should begin to study the artificial globe this morning. MOTHER. You already know what a globe or sphere is. When such a body has the different parts of the earth and sea drawn upon its surface, as they are in a map, and placed in their natural situation, it is called a Terrestrial Globe, and really represents the planet we inhabit. If the fixed stars and the constellations are represented on a sphere, it is then called a Celestial Globe. The motion of the terrestrial globe should be from west to east in order to imitate the real motion of the earth on its axis. The motion of the celestial globe, on the contrary, should be from east to west, because it is to represent the apparent motion of the heavens round the earth. WILLIAM. How can a globe give us any idea of the situation of the stars? The sky appears arched, like a vault, over our heads, with all the stars fixed in the hollow side of it; not like part of a globe. MOTHER. And therefore, when we use the celestial globe, we must suppose ourselves to be in its centre, or on the earth at its centre; and with a little practice you will find no difficulty in doing this: : "If we imagine a large hollow sphere of glass to have as many bright studs fixed on its inside as there are stars visible in the heavens, and placed at the same distances from each other as the stars appear to be, the sphere will be a true representation of the starry heavens, to an eye supposed to be in its centre, and viewing it all around; and if a small globe, with a map of the earth upon it, be placed on an axis in the centre of the starry sphere, and the sphere be made to revolve on this axis, it will represent the apparent |