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either the common, which is formed by athread or chain equally thick, or equallyheavy in all its points; or uncommon,which is formed by a thread unequallythick, that is, which in all its points is un-equally heavy, and in some ratio of theordinates of a given curve.” (See page

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491, omnia opera.)

To draw the common catenary mechani- Fig. id.bally.

Suspend on a vertical plane a chain ofsimilar and equal links of homogeneousmatter, as flexible as possible, from anytwo points not in a perpendicular line, norSo distant from each other as the length ofthe chain. Prick the plane through thelinks as nearly as possible in the middle ofthe chain, and through the points draw thecatenary.

If the chord F B D oi F b d be given,and the absciss B A or b A intersecting itin B or b at a given angle. Draw the ver-tical line B A, and F B D or F b d at thegiven angle on the plane. Fix one end of

f 2