Page:Report from the Select Committee on Steam Carriages.pdf/154



Mr. Richard TrevithickDavies Gilbert [sic]. 17 August, 1831.  being a given quantity as well as the force requisite for impelling a given weight up a given ascent, the power required for moving Steam Carriages on a Rail-way remains theoretically independent of its speed, and practically increases but a very little, in consequence of resistances from the atmosphere, slight impacts against the wheels, inertia of the reciprocating piston, &c. The expenditure of what I have termed Efficiency, is as actual force multiplied by the velocity, and the consumption of fuel in a given time will be in the same proportion, but the time of performing a given distance being inversely as the velocity, the expenditure of fuel will theoretically be constant for a given distance, and very nearly so in practice. The power requisite for moving bodies through water is in the opposite extreme; here, the mechanical resistance of the fluid increases with the square of the velocity, as do the elevation of the water at the prow and its depression at the stern. The cars or paddles must therefore preserve a constant ratio to the velocity of the vessel; and the force applied will consequently vary as the squares of the velocity, and the expenditure of Efficiency being as the force multiplied by the velocity; the consumption of fuel will be as the cube of the velocity in a given time, or as the square of the velocity on a given space; and I have ascertained from the records of voyages performed by Steam vessels, that the law is nearly correct in practice: hence the great power required for such Steam vessels as are constructed not merely for speed, but also to set at defiance the opposition of winds and seas; while, on the contrary, a very small power will be found sufficient for moving ships of the largest dimensions through the water, at the rate of two or three miles an hour, when their sails are rendered useless by continued calms." 



is your profession?—I have no profession; I am pursuing the introduction of locomotive Engines on common roads. 