Before we learn the distance of the Moon we have to think a little about her size. You have not yet learned about the size of our Earth, so we will take the two friends together. There are two ways of measuring a ball or globe. We may say how big it is _through the middle_, from one side to the other. Or we may say how big it is _round the outside_. The outside measure is always about three times as much as the through-measure. A large grape may be one inch through, and three inches round outside. A small orange may be two inches through, and six inches round outside. A large apple might be three inches through, and nine inches round outside. A small cocoa-nut might be four inches through and twelve inches round outside. A school-globe might be one foot through and three feet round outside; or two feet through, and six feet round outside. A balloon might be twenty feet through and sixty feet round outside. Or it might be thirty feet through, and ninety feet round outside. The through measure is called the _Diameter_ of a ball, and the outside measure is called its _Circumference_. A globe may be of any size; and it can be measured according to its size in inches, or feet, or yards, or miles. Our Earth is a little less than _eight thousand miles_ through, from side to side, or from north pole to south pole. Its outside measure, right round the equator, is nearly _twenty-five thousand miles_. This will not give you any clear idea. It only sounds very large. Think first of a mile. One mile is a good way for a little child to walk; but not much for a big boy. Some people count five or six miles a very long walk, while others think nothing of ten or twelve miles. Not many men can do as much as thirty or forty miles in a day. But even fifty miles are only half of one hundred. And it takes ten hundreds to make one thousand. And the through-measure of our Earth is eight thousands of miles. If that man, whose story you heard in the first chapter, ever had really done as the story says, and walked round the whole world, he would have gone about twenty-five thousand miles! How long would that have taken him? Certainly very much longer than twenty-four hours. He could not possibly have got along at the rate of one thousand miles and more each hour. The fastest express train does not manage over sixty or seventy miles in an hour. If he had journeyed all the while, Sundays and week-days alike, twenty miles each day, then he would have got round the world in three years and a half. And if he had only done ten miles a day he would have been nearly seven years getting round. Of course no man could really cross the oceans on foot; but this will help you to a little notion of what the size of our Earth is. A very big globe, is she not? yet not truly large, compared with other larger worlds in the sky. Our Moon is not one of those larger worlds, however.