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. MOTION AT THE SADDLE AS WHEELS ROLL OVER AN OBSTRUCTION. [Illustration: Fig. 1. Ordinary, 52 F., 18 R.; 4-in. obstruction; saddle twenty degrees back.] [Illustration: Fig 2. Rational Ordinary, 52 F., 18 R.; 4-in. obstruction; saddle thirty degrees back.] [Illustration: Fig. 3. Lever Rear-driver Star, 18 F., 52 R.; 4-in. obstruction; saddle twenty degrees forward.] [Illustration: Fig. 4. Star, 20 F., 52 R.; saddle vertically over axle.] [Illustration: Fig. 5. Star, 24 F., 39 R.; saddle over axle.] [Illustration: Fig. 6. Kangaroo, 40 F., 18 R.; saddle twenty-five degrees back.] [Illustration: Fig. 7. Rear-driver Rover, 30-in. wheels, eleven inches apart; saddle forty inches high, twelve inches forward.] [Illustration: Fig. 8. Rear-driver, 30 F., 24 R.; saddle forty inches high.] [Illustration: Fig. 9. Dennis Johnson, 30-in. wheels; saddle thirty inches high, midway between wheels.]