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Sir Is A Ac New to n’s Book!.

equivalent to weights, fiich as the force of a man’s arm, aftream of water, or the like.

go. But to comprehend the meaning of this rule, thereader muft know, what is to be underftood by reciprocalproportion ; which I lhall now endeavour to explain, as di-ftin&ly as I can; for I fhall be obliged very frequently tomake ufe of this term. When any two things are fe> related,that one increafes in the fame proportion as the other, they aredire&ly proportional. So if any number of men can performin a determined fpace of time a certain quantity of any work,fuppofe drain a fifh-pond, or the like ; and twice the num-ber of men can perform twice the quantity of the fame work,in the fame time; and three times the number of men canperform as foon thrice the work ; here the number of menand the quantity of the work are directly proportional. Onthe other hand, when two things are fo related, that one de-creafes in the fame proportion, as the other increales, theyare faid to be reciprocally proportional. Thus if twice thenumber of men can perform the fame work in half the time,and three times the number of men can finifh the fame in athird part of the time ; then the number of men and thetime are reciprocally proportional. We fhewed above a howto find the common center of gravity of two bodies, therethe diftances of that common center from the centers of gra-vity of the two bodies are reciprocally proportional to the re-fpedive bodies. For C E in fig. j 6 . being in the fame pro-

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portion