Mechanics,

equal Weight with another that is a Stand-ard. The Proportional Balance is withoutScales, and is used for discovering or assign-ing any Proportion of Weight in Bodies*The False Balance makes Bodies of unequalQuantities of Matter appear to have equalWeight. Lastly, the St at er a, or RomanBalance , commonly called the Steelyard, is •a most useful Kind of universal Balance,the Structure and Use whereof will beeasy to understand from the above Prin-ciples.

II. The PULLEY is an Instrumentwell known; if single, it is reduced to theLever of the fifth Sort, or Balance, andso affords no Advantage in raising Weights.If two or more .be combined together inthe common Way, Then the Power is tothe Weight as Unity to the Number of Ropeswhich goes to the Pulleys of the lower Box.But there are different Ways of applyingPulleys, whose Advantage or Power will beobvious from a View of the Structure ofthe several Sorts of Tackles, and the Expe-riments with them.

III. The WHEEL and AXLE (com-monly call’d the Axis in Peritrochio) is thethird Mechanical Power. We easily fee byits Make it is reducible to a Lever of thefirst Sort; and that therefore the Power is

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