“You can familiarize yourself in another way with the double movement of the terrestrial globe, as follows: place in the middle of a room a round table, and on that table a lighted candle to represent the sun. Then circle around the table, pirouetting on your toes. Each of your pirouettes corresponds to a turn of the earth on its axis, and your course around the table corresponds to its journey around the sun. Notice that in turning on your toes you present in succession to the rays of the candle the front, one side, the back, and the other side of your head, which in our experiment may represent the terrestrial globe; so that each one of its parts is in turn in the light or in the shade. The earth does the same: in turning it presents one after the other its different regions to the rays of the sun. It is day for the region that sees the sun, night for the opposite region. That is the very simple cause of day and night. In twenty-four hours the earth makes one rotation on its axis. Of these twenty-four hours the duration of the day and night is composed.” “I understand very well the cause of the alternation of day and night,” said Jules. “It is day for the half of the earth that sees the sun, night for the opposite half. But as the globe turns, each country comes in succession to face the sun while others pass into the unlighted half. The lark that turns on the hearth presents, in the same way, each of its sides in turn to the heat of the flame.” “One might almost say,” remarked Emile, “it is day for the half of the lark next to the fire, and night for the other half.” “One difficulty still perplexes me,” Jules continued. “If the earth turns around once in every twenty-four hours, in half of that time we ought to make a half-turn with the globe that carries us, and find ourselves upside-down. At this moment we have our heads up, feet down; twelve hours later it will be just the opposite: our heads will be down and our feet up. We are upright, we shall be upside-down. In that inconvenient position why don’t we feel uncomfortable? Why are we not thrown down? So as not to fall, it seems to me, we ought to be obliged to cling to the ground in desperation.”