238

MOTIVE POWER EMPLOYED

hour = 400, as the general expression of hisperformance for twenty miles : and consideredthat in travelling twenty miles at any otherrate of speed, his effect would not be greater ;at least, I considered that the extra muscularexertion required to transport his own weight,which is more than seven times that which isexerted upon the load, would be equal to thatdiminution of weight, which, multiplied intothe speed, would make the sum of his effortremain the same, and equal to 400.

Taking this rule, and making v — the velo-city in miles per hour, we have 224 lbs. as theeffort of a horse at one mile an hour, and — -his effort at any other rate of speed ; or, making400 as the expression of his performance of theweight multiplied into the velocity, we haveas the weight which he will drag upon alevel Rail-road at any other velocity.

Since forming my calculations, I find Pro-fessor Leslie, in IiIb Elements of NaturalPhilosophy, had previously given a formula forcalculating the force which a horse can exertupon the load at different rates of speed.

He states, “ with regard to the power ofdraught, the formula (12— vf, when v denotesthe velocity in miles an hour, will perhaps befound sufficiently near the truth.—Thus, if ahorse beginning his pull with the force of