A Course Of Lectures In Natural Philosophy

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1739 edition. Excerpt: ... LECTURE VIII. Of Compound Engines. Lect.t, he mechanick powers, which for the moft VIII... part are made ufe of feparately, may in ma-Vy-' ny caes De combined together, and engines thereby formed of fuch efficacy, as that by the help thereof exceeding great weights may be raifed by very fmall powers. In all fuch compounded machines the proportion, which the moving power bears to the weight when they balance each other, is compounded of the feveral ratios which thofe powers have to the weight which balance it in each fimple machine, whereof the compounded engine confifts. Thus when a machine is compofed of an axle in the wheel and a pulley, by fattening the drawing rope of the one to the axle of the other; the power which balances the weight in fuch a machine muft be to the weight, in a ratio compounded of the ratio which that power has to the weight which balances it by means of the axle in the wheel alone, and of the ratio which that-power has to the weight, which balances the weight by means of the pulley alone. Exp. i. For inftance, if the nature of the pulley be fuch, as that a power equal to one tenth part of the weight balances it; and if the axle in the wheel be fuch, as that a power equal to one fifth part of the weight can rupport it; the power, which balanceg the weight in the compounded machine, will be to the weight in a ratio compounded of one to ten, and of one to five, that is, it will be to the weight as one to fifty;. for, fince the weight is in effect fattened to the axle of the wheel by means of the rope which goes round the pulleys, it is evident that the axle will be drawn by a force equal to that, which when applied to the drawing rope of theLEcT pulley is requifite to fuftain the weight by means of VIII. the pulley, .