I ZO Tshe consequences of the

whole quantity of motion can never be keptup, among any sort of particles, unless whereall the directions conspire, and are neveschanged, which is never the cafe in mecha-nical motion. From this consideration, thefollowing important consequence, in thiskind of motion, is plain. That a power tsnot only necessary to impress the motion atfirfi jbut that it must act incessantly , to keep it upto one constant pitch. The force or energyof every single impulse of this cause ab extra,is extinguished in whole, or in part, by theaction and re-action of the moving particlesof the system; the last always consumingthe first, as well as being equal to it: so thatthe motion would soon cease altogether, with'out the indesinent action of the original po we s-Our experience in machines contrived by theart of man confirms this. It would be ab'surd to think that one single impulse of thespring of a watch would keep it going f° sany time after. The weight must constantsact on the clock. The natural power of g ra 'vitation consists in repeated successive impulse

XV. By a machine can only properly b 2meant a sysiem of matter so disposed , that th 1

faed