262 THE MATHEMATICAL PRINCIPLES [BoOK 11 proportion, as nascent. It will be the same thing, if, instead of moments, we use either the velocities of the increments and decrements (which may also be called the motions, mutations, and fluxions of quantities), or any finite quantities proportional to those velocities. The co-efficient of any generating side is the quantity which arises by applying the genitum to ihat side. Wherefore the sense of the Lemma is, that if the moments of any quan tities A, B, C, &c., increasing or decreasing by a perpetual flux, or the velocities of the mutations which are proportional to them, be called a, 6, r, (fee., the moment or mutation of the generated rectangle AB will be «B -h b A ; the moment of the generated content ABC will be aBC -f b AC 4 -1 -2. .1 cAB; and the moments of the generated powers A2. A3, A4, A2, A2. A3, A*, A — ', A — 2, A— * will be 2aA, 3a A2, 4aA3,