Differentiating and equating to zero, the cost is least when dC _ **LP** +La =o, dl = l2 P=ale=G; that is, when the cost of one pier is equal to the cost erected of the main girders of one span.

Draw **LP** upward and some convenient multiple of Ll.

Hence the total cost of that part of the bridge which varies with the span adopted is C = (n-i)P-FnaP = **LP**// - P +Lal.

Of the Memoires de la societe de l'histoire de Paris et de l'p le de France.

Then, the crank standing at any angle with the line of stroke, draw **LP** at right angles to the connecting rod, PN at right angles to the line of stroke OB and NA at right angles to the connecting rod; then AO is the acceleration of the point B to the scale on which KO represents the acceleration of the point K.

Then, the crank standing at any angle with the line of stroke, draw **LP** at right angles to the connecting rod, PN at right angles to the line of stroke OB and NA at right angles to the connecting rod; then AO is the acceleration of the point B to the scale on which KO represents the acceleration of the point K.

1(/?hi Sh f f ord - o' °kle d o ?eb >, ?y pt{**lp** h S d n?

L.,' **lP** °Faimouth Ys Seymour Long Pt.

TpE- €**LP**; Skeat (Etym.