Pa. No; for it moves in empty space.
Lu. What, does it not move through the air?
Pa. The earth does not move through the air, but carries the air along with it. All the air is contained in what is called the atmosphere, which you may compare to a kind of mist or fog clinging all round to the ball of the earth, and reaching a certain distance above it, which has been calculated at above forty-five miles.
Lu. That is above the clouds, then.
Pa. Yes: all the clouds are within the atmosphere, for they are supported by the air. Well—this atmosphere rolls about along with the earth, as if it were a part of it, and moves with it through the sky, which is a vast field of empty space. In this immense space are all the stars and planets, which have also their several motions. There is nothing to stop them, and therefore they continually go on, by means of the force that the Creator has originally impressed upon them.
Lu. Do not some of the stars move round the sun, as well as our earth?
Pa. Yes; those that are called planets. These are all subject to the same laws of motion with our earth. They are attracted by the sun as their centre, and form, along with the earth, that assemblage of worlds, which is called the solar system.
Lu. Is the moon one of them?
Pa. The moon is called a secondary planet, because its immediate connexion is with our earth, round which it rolls, as we do round the sun. It, however, accompanies our earth on its journey round the sun. But I will tell you more about its motion, and about the other planets and stars another time. It is enough at present, if you thoroughly understand what I have been describing.
Lu. I think I do.