THE DISCOVERY OF PLANET NEPTUNE.
"How could that happen?" asked Harry.
"Because Uranus behaved so strangely," replied his sister. "The planets attract each other; for instance, the earth is swayed to and fro by Jupiter and Venus, and a great struggle is always going on among the planets in the family of Giant Sun. It could be plainly seen that Saturn was taking part in the struggle and dragging Uranus toward it, but something beyond the newly discovered planet was pulling it the other way. 'There must be another planet,' said the astronomers, and they were right. After puzzling over the problem two astronomers found the truant, and announced exactly when and where it was to be seen. And there it was, nearly exactly where these learned men said it would be. The new planet was christened Neptune, and it takes about one hundred and sixty-four years to go around the sun. It is so far away from the sun that it only receives one nine-hundredth of the amount of light and heat we receive on planet earth."
"Then it must be very cold on planet Neptune?" said Harry.
"And very dark also," said Mary, "since from this planet the sun only looks as large as an electric light seen at a distance of a few feet."
SIZE OF PLANETS, COMPARED WITH THE SUN.