LIGHTER VEHICLES.--The tendency of the day is toward lighter vehicles, brought about, in a large measure, by improved materials in every direction. It is no longer urged that heavy, ponderous machines are required to furnish stable and durable vehicles. Nothing can stop or retard this great industry. It is attractive to men and fascinating to boys. To acquire a knowledge of its “mysteries,” should be a part of the education of every young man. CHAPTER II THE FRAME, AND ITS ACCESSORIES Under this title should be included the frame, axles, springs, wheels, steering gear and brakes. From the beginning it was recognized that the different strains and stresses set up by the passing of the wheels over uneven ground and by the motor and driving mechanism, must be taken care of before reaching the body of the automobile, which otherwise would soon go to pieces. [Illustration: Fig. 1. Views of Plain Frame.] THE FRAME.--Therefore, not only springs had to be interposed between the body and the wheel axles, but also a substructure for the body, called the frame, which must be rigid enough to prevent any destructive strains from reaching the body. In Fig. 1, A shows a top view of a frame made up of channel bars and B shows a side view to illustrate how the torsion or twist takes place. It will be understood that the frame thus made is not designed to lend itself to the entire inequalities of the road, as the springs are interposed for that purpose. Experience in the construction and use of tubular frames, as first employed in bicycles, proved too expensive for assembling, when used in automobiles. The tubular form of construction was very soon displaced by frames consisting of metal parts bolted or riveted together. The main or side members are now usually made of channel steel which gives great rigidity and strength, compared with its weight. [Illustration: Fig. 2. Quarter Elliptic.] HOW THE FRAME IS SUSPENDED.--The important feature is to mount this frame on the axle. The frame, carrying a body and all the load of the vehicle, has to permit three distinct movements. First. That due to the inequalities of the road, which produces a torsional twist. Second. A lateral swing, caused by traveling alongside a hill, or due to centrifugal force when making a turn rapidly. Third. A fore and aft movement, as when traveling over undulating surfaces, or in suddenly stopping and starting. [Illustration: Fig. 2a. Half Elliptic.] For these reasons springs must be made to compensate for such motions, and to absorb the jar as much as possible. [Illustration: Fig. 3. Three-quarter Elliptic.] THE SPRINGS.--Many forms of spring mountings have been devised, but the following illustrations show the types which set forth the principles involved. Outside of coiled springs which are used in some forms of delivery cars, the standard springs are leaf springs, built up from a number of steel leaves. There are four distinct forms of springs used, as follows: