[Illustration: Paper Gliders. Antoinette Monoplane and Wright Biplane] [Illustration: An excellent glider with wooden planes] [Illustration: A covered-frame sling-shot glider] The best glider for launching on the sling-shot principle is made from planes cut from thin metal sheets. Aluminum is the best material, but a very thin wood will answer. A one-foot model glider will be found the easiest size to manage. Cut one plane eight inches in length by three in width, and the second five inches by two inches. Round off the corners on one side of each plane, leaving a straight line for the front or entering edge. Mount the planes on a strip of reed, cane or bamboo about eighteen inches in length. In all these gliders the forward plane is made the smaller, thereby reducing the head resistance as far as possible. The metal planes should be slightly flexed by bending them to a slight concave above the horizontal and just back of the front edge. The forward end of the stick should be bent into a large hook by heating or first soaking in water. If your glider falls quickly to the ground bend the frame a trifle upward. Since your glider is intended to travel at a comparatively high speed, the planes may be mounted much further apart than in the case of a glider launched from the hand. Try them first ten inches apart and afterwards adjust them to suit. The rubber used for launching the glider should be fairly heavy, say three strands of one-eighth inch rubber or its equivalent. The end of the hook may need adjusting so that it will escape from the rubber on being released. It will be found an easy matter to obtain long, graceful glides from this model from the first. By launching it upward, it may rise to a considerable height. When you have caught the trick of launching your glider with sufficient force, try a spectacular flight. Set your forward plane at an angle by inserting a block of wood between the stick. In the case of metal planes, bend up the front edge. A very slight upward elevation will answer. Gradually increase this angle until the model sweeps upward and turns on itself. You will soon be able to make the glider describe a complete circle or loop the loop twice before landing. When traveling at such a high rate of speed, your glider is likely to be dangerous and might inflict a bad cut, and the flight should only be attempted where one has plenty of room. These flights may be still further varied by adjusting the rear edge of the vertical plane or rudder. By turning the rudder to the right, for instance, the glider may be made to travel to the right or the direction may be reversed. In this way the glider may be made to describe a complete horizontal circle or several circles. By launching the glider upward with this adjustment, it may be made to fly in a graceful spiral.