CORRESP ONDENCE. 



267 



CORRESPONDENCE. 



TA n 



EIGHTING THE BICYCLE. 



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 supple- 

 mentary statement to make it comolete. 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 phys- 

 ics that the center of gravity of a body must 

 be over some point in its base in order that 

 the body may stand 

 without outside sup- ^ 



port. Now, the base 

 on which a bicycle 

 rests is only a line 

 about half an inch 

 wide, which joins the 

 point B, in ray 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 out- 

 side 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 equiva- 

 lent, 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 di- 

 rection 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 0, parallel to the new course of 

 the machine. The result is, that it takes an in- 

 termediate 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 jo. 

 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 fall- 

 ing bicycle in motion involves two move- 

 ments : 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 ray ex- 

 planation. I will add that I ride a bicycle 

 myself, and so am acquainted with this mat- 

 ter on the practical as well as on the theoreti- 

 cal side. Very truly yours, 



Fredekik a. Fep.nald, 

 L. A. W., 12,99G, 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.] 



THE KELLEY'S ISLAND GROOVE. 



Editor Popular Science Monthly : 



Dear Sir: In this month's number of 

 the Science Monthly, under the " Miscella- 

 neous " 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 occupa- 

 tion for them must seem to those who know 

 them very inappropriate. Prof. Wripht 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- 

 hlood. It is not Y onn^blood, 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. 



