Page:Popular Science Monthly Volume 40.djvu/279

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Editor Popular Science Monthly:

SIR: The article What keeps the Bicycler Upright? in the Monthly for last April was a very interesting one, especially to wheelmen, but I think it needs a little supplementary statement to make it complete. Mr. Charles B. Warring, the author, states that the rider's lost equilibrium is restored by bringing his point of support under him, and gives the impression that this point can be moved square to the right or left, like the foot of Mr. Warring's A-frame, saying nothing about the forward movement of the wheel. While agreeing with the main part of this statement, I think the righting of a bicycle can be more clearly and accurately explained as follows:

It is one of the elementary laws of physics that the center of gravity of a body must be over some point in its base in order that PSM V40 D279 Bicycle upright equilibrium explanation.png the body may stand without outside support. Now, the base on which a bicycle rests is only a line about half an inch wide, which joins the point B, in my figure, where the front wheel rests on the ground, with the point C, where the rear wheel rests. (I adopt Mr. Warring's lettering.) So long as a vertical line dropped from the center of gravity of the machine falls on some point of the line B C, the bicycle is in stable equilibrium; but, when it falls outside this narrow base, as at the point D, the equilibrium becomes unstable. In order to keep the machine and rider from coming to the ground, D must be brought upon B C; or, what is equivalent, B C must be brought under D. The latter is what is actually done. As the rider can not slide his machine sideways over the ground, he steers it obliquely toward the side on which he tends to fall. Thus, if the bicycle were running in the direction C m, he turns it toward the right so as to go in the direction B p. The center of gravity of the machine and its rider, which had been moving parallel to the course of the machine, is now acted on by two forces: (1) its acquired momentum, which tends to carry it on in the direction D n, and (2) the force constantly being received from the moving bicycle, which tends to carry it along the line D o, parallel to the new course of the machine. The result is, that it takes an intermediate direction, D p, in accordance with the law of the composition of forces. Thus, by being made to follow converging lines, D and B C are brought together at the point p. As quick as this is accomplished the bicycle must be turned again parallel to its original direction, or D will pass over to the left of B C and make the machine tilt toward that side. Hence, it is seen that righting a falling bicycle in motion involves two movements: first, a turn of the machine toward the side on which it tends to fall, then a return to its original course. Gravity was not mentioned among the forces considered above, but its action does not vitiate my explanation. I will add that I ride a bicycle myself, and so am acquainted with this matter on the practical as well as on the theoretical side.

Very truly yours,
Frederik A. Fernald,
L. A. W., 12,996, N. Y. Division.

[Substantially the same explanation as that given above has also been received from Mr. Thomas Gary Welch, of Buffalo, N. Y.—Editor.]




Editor Popular Science Monthly:

Dear Sir: In this month's number of the Science Monthly, under the "Miscellaneous" head, you have a notice of the work now in progress for the preservation of the great glacial groove on Kelley's Island.

In that notice you speak of Prof. Wright and Dr. Sprecher as having "surveyed" the plot of land on which the groove is located. In this statement you are in error. They are not surveyors, and they did not survey the plot, and the suggestion of such an occupation for them must seem to those who know them very inappropriate. Prof. Wright is Professor of "New Testament Greek" at Oberlin, and the author of that noble book. The Ice Age in North America, published by the Appletons in 1890; and Dr. Sprecher is pastor of one of the largest Presbyterian churches in our city. And in that notice you make another error, which to me seems very absurd. You give my name as Young-blood. It is not Youngblood, as you may learn from your subscription list, where it has been recorded from the time that the first number of the Science Monthly was issued.