CHAPTER VIII.
COMPARISON OF THE CURVES OF TRANSLATION, IN MACHINES OF WHICH THE DIAMETERS OR COMBINATION OF WHEELS DIFFER, OF A POINT TAKEN IN THE SAME RELATIVE POSITION ON THE SEVERAL SADDLES—CONSEQUENT CONCUSSION AND EFFECT UPON MOMENTUM.
In discussing this matter it has been taken for granted that the proper point upon which to base calculations is that point in the saddle at which the motion of the machine may be supposed to be transmitted to the rider; this happens to be very near the centre of gravity of the system, and is also quite near the centre of gravity of the man. The motion is of course partially transmitted to the rider at the pedals, but we will for the present waive that modification.
Simple as the running of two wheels over an obstruction seems to be, there are some interesting points to study. It was a surprise to the writer, and it is his hope that it may be of interest to others, that the saddle, and of consequence the rider, actually goes backward at times when the wheels are running forward; as, for instance, when the machine rolls slowly from a four-inch obstacle, as shown by the curve of the point in the fifty-two-inch Ordinary given below, and also particularly in the advance upon the same of the Star rear-driver. This reversion of momentum sometimes results in a drop of the rear wheel, but it is always an actual reacting force in the front. We feel the curves very plainly on a rigid machine, but it is a satisfaction to know exactly what they are and what the springs must overcome.