Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: LESSON FIFTH. When a pendumm to a clock swings backwards and forwards, does it move in a straight line? It does not; the line is curved like a part of a circle. Why does it not. swing quite around the place where it is fastened, just as the ball does when you whirl it round your hand 1 The attraction of gravitation draws the pendulum down towards the ground when it begins to go up. Then why does not the pendulum stop, instead of going up the other side ? Because it goes down so fast that it cannot stop in an instant. What is this like ? Like a boy sliding down hill. How does he go ? He goes so fast down the hill that when he gets to the bottom he cannot stop, but goes part way up the next before the sled stands still. How would it be if somebody should push him down this second hill? He would go part of the way again up the first. And how is this like a pendulum ? When my hand strikes the pendulum, it will go down as far as it can, and because it cannot stop itself it will go up the other side. What will it do then ? The earth will draw it down again so fast as to send it up the side from which it started. How long will it go so ? Sometimes it will go a great many days. Could it not be made to go forever without stopping ? It could not. Why could it not ? Because the attraction of the earth would finally stop it. What amusement have the Russians like sliding down hill ? They have a Mountain of Sledges. Can you tell how it is made ? It is a kind of wooden mountain, made of three hills, one above the other, with a valley between each hill. How do they get to the top of it ? They walk up one hill, then down into the little valley, then up a higher hill, and down into another valley, and then up into t...