পাতা:পদার্থবিদ্যাসার.djvu/৩৩

Tut. Because the air, or atmosphere, which encircles the earth, is carried along with it; and all surrounding objects umove with us at the same time. Pup. Has ihe eartli any other motion : Tut. Wes: besides its annual motion round the sun, it has another round its own axis, called its diur. nal motion, which makes our day and night. In this double motion it resembles the wheel of a carriage running round a circle, which proceeds forward, and turns on its own axle at the same time. Pup. At what rate doesthe earth revolve on its axis? Tut. At the rate of one thousand miles an hour, Pup. Does the moon move round the earth 3 Tut. Yes, in about twenty-nine days and a half: if continually attends upon the earth during its whole revolution round the sun. Pup. W Iiy do we not always sce the moon Tut. When it is on that side of the earth next the sun, then the dark side of the moon is towards us; for which reason we are not able to see it. It is also frequently below our horizon, and therefore in. visible. Pup. What au I to understand by am eclipse? Tut. When the moon's shadow falls upon the eartlı, we call that an eclipse of the san, because the moon prevents our seeing the Sun, more or less, according to the extent of its shade. And when the shadow of the earth sails upon the moon, we call that an eclipse of the moon. Pup. When do eclipses of the sum happen? Tut. Only at new moon. -