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Page:Popular Science Monthly Volume 38.djvu/792

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reference to them it is in stable equilibrium, while in regard to side motion its equilibrium is very unstable; the least thing will upset it.

To study the matter more conveniently, I have had a form made which eliminates all unnecessary parts and represents only

PSM V38 D792 A safety bicycle with lines of force.jpg
Fig. 7.—A "Safety" Bicycle, with Lines of Force.

the lines of force and the weight on the saddle (Fig. 8). It consists, as you see, of two long, slender pieces of pine, and looks like a huge capital A, the cross-piece serving merely to hold the whole more firmly together. At the apex, A, I have placed a few pounds of lead to represent the rider's weight. PSM V38 D792 Apparatus ilustrating how a bicycle is kept upright.jpgFig. 8.—Apparatus illustrating the Way a Bicycle is kept Upright. In the older form of the bicycle, the wheel in front is very much the larger. The corresponding leg, A B (Fig. 8), is much steeper and shorter than the other. In "safety cycles" it is just the reverse, the rear leg being steeper and shorter, while the two wheels are of nearly the same size. As the theory of both machines is the same, I shall, the present, for speak only of the former.

For convenience in handling, and that it may be better seen, I place the foot C, the rear one, on the table, and hold the other, B, in my hand, and at the same height from the floor. Now, notice: the weight at the apex, or saddle, begins to tilt to the