WHAT KEEPS THE BICYCLER UPRIGHT? 773 



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 sup- 

 port 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 bot- 

 tom 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 giv- 

 ing 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 ma- 

 chine 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 



VOL. XXXVIII. 54 



