"There is no fear of that," said his sister Mary, laughing at the idea. "But a long time ago people asked the very same question. In those days they thought the earth was flat, and surrounded by an ocean without end. The Hindoos supposed that the earth rested upon four elephants, and the four elephants stood on the back of an immense tortoise, which itself floated on the surface of an endless ocean. It was thought that the sun plunged into the ocean when it disappeared in the evening, and some people said they heard a hissing noise when the red-hot body went under the waves. "But if the sun dropped into the water each evening, how did it happen that next morning it was seen again, as hot and bright as ever? The people could not tell why, so they said that during the night the gods made a new sun to be used the next day." "That must have kept them busy," said Harry, laughing. [Illustration: ANCIENT IDEA OF THE EARTH.] "The good people made up another story about the sun, so that the same one could be saved each night. Just as it was dropping into the ocean, a god named Vulcan, who had a great boat ready, caught it, and all night long he paddled with the blazing sun. Next morning he was ready at sunrise to send the sun up into the sky in the east. He threw it with so much force that it would go very high, and when it came down on the other side in the west, he stood ready to catch it again." "But where does the sun really go to at night?" asked Harry curiously. "I should like to know." HEAT OF THE SUN. [Illustration: ILLUSTRATING DAY AND NIGHT.] "We live on a big round globe called Earth," replied his sister, "and we travel round the sun, which gives the earth light and heat. The sun is like a great lamp in the sky, and when you face the lamp you see the light, but if you turn away from it you are in darkness. As the earth goes around the sun, it whirls around like a huge top; first one side and then the other is turned to the sun and gets sunlight, and so we have day and night. If the sun, or the lamp in the sky, went out and stopped shining, all the light would go out on the earth, and we would miss its heat as well. "It is so hot that if it kept coming nearer and nearer until it was as far from the earth as the pretty bright moon, the earth would get warmer and warmer and melt like a ball of wax." [Illustration] "Just like Nellie's doll, then," said Harry, "when she left it on the grass the other day. The sun was so hot that day that when Nellie picked up her doll, she found that its wax face had melted and the eyes had fallen in. So the sun did that," continued Harry, laughing heartily. "Poor Nellie! I must tell her that the next time I see her." "I can show you something else to prove how hot the sun is," said Mary, as she picked up a leaf from the ground. "Just wait a moment while I go into the house and get a magnifying-glass."