which the view of the world is taken. On the sea, or a plain, a man with perfect eyes can see a distance of about two and a half miles on a clear day. That is, he sees across a circle of five miles, or around a horizon of about sixteen miles. From a sky-scraper tower, two hundred feet above the earth, the same man can see nearly nineteen miles. From a mountain five thousand two hundred and eighty feet, or a mile high, he can see nearly one hundred miles in every direction. We can see farther by going up higher, because the earth is a sphere, or globe. The surface of it slopes away on all sides. At a certain distance, on a level, the slope falls below our vision. As we go higher, farther limits come up within range of our eyes.
WHY THE EDGES OF COINS ARE "MILLED"
Have you a silver dollar, or a gold piece? A Your papa has. Perhaps you never noticed that coins are cut in regular up and down grooves around the edges. This is called "milling," because it is done in the government money mill, or mint. Coins have been milled for so long a time by all countries, that no one knows just when the practice was begun. But the reason for it is very well known. Dishonest people used to shave away thin layers from the edges of coins. When the edges were smooth this could be done, and no one could detect the theft unless the coins were weighed. When the edge is grooved or milled, stealing in that way is not so easy. New grooves, as regularly spaced and as evenly cut, could not be made again, except by melting and re-minting the coin. Copper pennies and nickels are not milled, for the metal in them is not valuable enough to pay anyone for the trouble of shaving the edges away.
HOW TRAINS RUN AROUND CURVES
The first law of motion, as you learned in what keeps a bicycle upright, is that a moving thing goes forward in a straight line. If the direction of the moving is changed some other force must come into play. What force will interfere with a forward movement on a level? Why a rise in the level. It is harder to go up hill. To make a little hill the outside rail is raised quite a little higher than the inside rail. The height to which the outside rail needs to be raised depends upon the sharpness of the curve, and the speed at which trains are expected to run around it. Around very sharp curves trains must "slow down" to keep from running off the track. When you run around a corner, or ride around one on a bicycle, you lean
