I think the above sufficiently exposes the sophistry of the wide-tread theory, but lest some of the old adherents to the idea should not be willing to accept Mr. Stoney’s mechanical reasoning, I have had made a device to test the matter in this way (see Fig. 3). [Illustration: Fig. 3. Roller experiment.] We have an upright frame provided with two cross pieces, _bc_ and _ef_, a saddle at _a_, rests for the feet at _b_ and _c_, and a roller, _d_, placed under _ef_. Sitting upon the saddle _a_, I was totally unable to move the roller _d_ by any pressure upon either pedal _b_ or _c_. The above I consider conclusive proof and the result unbiased by prejudice in trying the experiment, because I tested the matter before looking carefully into Mr. Stoney’s article and becoming convinced that in this he is right. The laws applying to internal forces or forces within a system are very often disregarded, and especially are internal confounded with external forces, as in this case. In any machine where the rider throws his weight on and vertically over the pedal, the formula given for the side-slip does represent a force acting to swing the machine out of perpendicular and to cause it to “wabble,” as Mr. Stoney calls it, but not to slip it on the surface of the roadway, as many would suppose. The rider rarely, however, throws his weight directly over the pedal sideways, as he does in raising upon it in a forward direction in order to get over the work. The lateral or wabbling strain in a cycle of the foot-pressure in one direction is balanced by the pull on the handle-bars and pressure of the leg against the saddle. The only feasible connection the formula theory can possibly have in this matter is that the thrust on the pedal is so sharp and violent that the inertia of the man and other heavy parts of the system are not perceptibly affected sideways; hence we might get an action against the slight weight in the lower part of the wheel. I cannot, however, detect any slipping action of this or any other kind in the roller experiment.