Page:Popular Science Monthly Volume 38.djvu/793

Rh right; I quickly move my hand to the right till it comes under the weight. If the saddle tilts to the left, I move my hand quickly to the left. In every case, by moving my hand more rapidly than the weight tilts, I bring the point of support under it. It is very easy in this way to keep the weight from falling; and that is the way the bicycle is kept upright.

But you will ask, How can the rider move the point of support when it is on the ground, and several feet out of his reach? He does it by turning the wheel to the right or left, as may be necessary—that is, by pulling the cross-bar to the right or left, and thus turning the forked spindle between whose arms the steering-wheel is held and guided.

But, some one will say, How does turning the wheel bring the point of support to the right or left—whichever the machine may happen to be leaning?

Let us suppose a 'cyclist mounted on his wheel and riding, say, toward the north. He finds himself beginning to tilt toward his right. He is now going not only north with the machine, but east also. He turns the wheel eastward. The point of support, B (Fig. 6), must of necessity travel in the plane of the wheel; hence it at once begins to go eastward, and, as it moves much faster than the rider tilts, it quickly gets under him, and the machine is again upright. To one standing at a distance, in front or rear, the bottom of the wheel will be seen to move to the right and left, just as I moved the foot of the skeleton frame a moment ago.

I conclude, then, that the stability of the bicycle is due to> turning the wheel to the right or left, whichever way the leaning is, and thus keeping the point of support under the rider, just as a boy keeps upright on his finger a broomstick standing on its smallest end.

It may be questioned whether the bottom point of the wheel really travels faster than the weight at the saddle tilts over, and, if it does not, then the explanation which I have been giving fails.

By an easy calculation, based on the well-known principle that the velocity of a body moving under the influence of gravitation varies as the square root of the height from which it has fallen, irrespective of the character of the path it has described, I find that when the rider's seat is, e. g., sixty inches high, and the machine has inclined, say, six inches out of the perpendicular, it is at that instant, if free to fall, tilting over at the rate of much less than a mile an hour. But six inches is a large amount to lean—a good 'cyclist does not lean that much—we will suppose him out of plumb only three inches; then his lateral movement will be at the rate of only some twenty-two hundred feet in an hour.. If the tilt is less, the falling rate will be less. To keep the center of