In speaking of different styles of bicycles, we will adopt the name “Ordinary” for the prominent form of machine which is provided with a large wheel fifty to sixty inches in front, with a crank movement, and the usual fifteen- to twenty-inch rear wheel. The recent rear-crank driver, with the two wheels of about equal size, we will recognize as the “Rover” pattern, in deference to the people who first pushed it into the market and so named it. Other terms will be adopted which will be self-evident to all acquainted with the art. Attention is called to the engravings in Part II. of this book, which will give an idea of the different forms of machines used in the art. [1] Animal Mechanism, 65. [2] J. Bell Pettigrew, M.D., F.R.S., F.R.S.E., F.R.C.P.E., “Animal Locomotion.” [3] E. J. Marey, College of France, Academy of Medicine, “Animal Mechanism,” 1887, p. 1. CHAPTER IV. THE DIRECT APPLICATION OF POWER. It is evident that one of the greatest, if not the very greatest, of the requirements of a practical road wheel, or a man-motor carriage, is that the power of the rider shall be transmitted to the said wheel in the most direct manner possible; that is, by causing the strain to come upon the muscles in such a way that these muscles shall be placed in the best possible position to overcome such strain, and to take advantage of such conditions as nature has already provided for, in training our muscles to the work we have had to do under the old _régime_, without the wheel. The muscles of man are best adapted to a direct pull or push. If we push upon a weight with the muscles at an angle to the direction in which we want the weight to move, the effective power is limited in the same way that the effect upon a weight is limited if we push at it in a direction at an angle to that in which we wish to move it; that is to say, not the total, but only a portion of the power will be effective in moving the weight. The above facts apply particularly to our subject when we desire to transmit motion to a wheel by means of the weight or gravity of our bodies. Gravity acting downward in a vertical line, if we are not placed over the resistance, the resultant effect is in proportion to the cosine of the angle at which we work, as follows: Let _W_ = the weight of the man and _a_ be the centre of gravity and also the location of the source of power of said weight, and let _c_ represent the point at which it is desired to apply the power to turn the wheel. [Illustration: Power angle.]