There are many other ways of making planes. If one does not care to round off the edges, he can make very light wooden rectangular frames of the size indicated, and cover them with cloth, or silk, afterward varnishing them to make them smooth and air-tight. It is difficult to give such planes a camber, but if the framework is made of strong light wire, such as umbrella ribs, and then covered, the camber can be obtained by putting light wire or light wooden ribs in the planes, much like on the big standard makes. Plane building can be developed to a high art, and after a boy makes one or two models he will see any number of ways that he can make them lighter, stronger and more professional looking. With the planes finished, the next work is to make the backbone of the machine by planing and sandpapering a light strong stick one foot long and not more than a quarter of an inch square. Cut out a neat block of the same wood, the same thickness as the backbone, and one inch square. Glue it to the end of the backbone and reinforce it by wrapping it with silken thread moistened with glue or varnish. Be sure to have the grain of this block, which is the motor base, run the same as the backbone. Three quarters of an inch from the backbone, and parallel with it, bore a little hole for the propeller shaft or axle. Unless you are sure of your drill, heat a thin steel wire and burn the hole, rather than risk splitting the block. The propeller is the next thing to make, while the glue on the backbone is drying, and the camber of the plane is setting. Some models have metal propellers, but most boys prefer to make wooden ones, either from blocks of their own cutting or from blanks that can be purchased. The blank should be four inches in diameter an inch wide, and half an inch thick. It can be cut away very thin with a sharp knife, and a fairly good whittler can make a propeller that looks as businesslike as the great gleaming blades on the big machines. A wire then should be run through the dead centre of the propeller and bent over so that when the wire shaft turns the propeller also turns. As a bearing or washer the simplest device is a glass bead strung on the shaft and well oiled to lessen the friction, between the propeller and the propeller base. The shaft is then run through the hole in the motor base and bent into a hook for the rubber strands that drive the propeller. Great care should be taken in mounting the propeller and making the hook that the shaft is kept in an absolutely straight line, and at an accurate right angle with the propeller, so that the screw can turn free and true with as little friction as possible, and no wobbling or unbusinesslike vibration. Next a wire hook should be placed at the other end of the backbone upon which to hook the other end of the rubber strands. This hook can either be imbedded in another block the same size as the motor base or can be set out by some other ingenious device, so that