24

links to be formed alternately of 4 or 5 plates, each plate to be 4 inches by7-8 inch thick. The length of the plates will vary from 5 to 10 feet.

The object of curving the chains is to place the last link in a vertical position,and to assist their tension by their pressure upon the masonry. The strain ofthe last link will thereby be reduced about one fourth; the same section of ironwill, however, be preserved throughout. A good quality of masonry, all to belaid in cement, is of course required, so that no appreciable settling will takeplace. The uplifting force of the last or vertical links being one-fourth less thanthe tension of the cables, is therefore 1070 tons: this pressure will have to beresisted by the weight of the superincumbent mass of masonry and embank-ment between the anchor or return walls. These walls, as far as they rest upona group of anchors, descend 15 feet below the pavement of the wharf, and willaverage 31 feet high; they are 7 feet thick on bottom and 5 feet on top, and asfar as they exert a pressure upon the anchors, they are 88 feet long. Theycontain, together with the buttresses, a quantity of masonry of 35,000 cubicfeet, wbich, at 130 pounds, weigh ----- 4,550,000 pounds.

The body of embankment between the walls is likewise sup-ported by the anchors, and measures 88 feet long, 22 feetwide and 30 feet deep, and contains 58,080 cubic feet, whichweigh, at 100 pounds, ------ 5,808,000 pounds.

Total weight upon anchors,. 10,358,000 pounds,

Or--------- - 5,179 tons.

To this must be added the resistance of the earth, stamped in outside, and whichpartly will adhere to the walls. We may safely estimate the total resistance at6000 tons, which is opposed to a pressure of 1070 tons. It may be asked, whyprovide for such an abundance of resistance ? In high water, the weight ofmasonry and embankment will be reduced about one-third. The depth of thewalls is necessary, to render the foundations safe : their thickness could not bereduced much without endangering their stability, and the embankmentbetween, which adds much to the weight, will cause no extra expense on thataccount.

c. Solidity of Foundations.

The greatest vertical pressure which the structure can exert upon the centretower, will be equal to the weight of 1180 feet of floor, cables and load. It willbe recollected, that this distance is the extent of the chord of that complete cat-enary, of which the cables form only a part. One-half of this span, or 590 feet,on each side of the tower, will fall to its support. The maximum weight of 1foot of floor being 11-2 ton, including all, we find the weight upon the tower

equal to---------- - 1,770 tons.

The tower itself contains 12,000 perch, or 300,000 cubic feet of

masonry, which, at 130 pounds, weigh - 19,500 “

Total weight upon foundation of tower.21,270 tons.

The superficial area of the lowest course will measure 2,600 feet; this, divided

in the above weight gives about 8 tons for every foot. This is far within thesafe limit of the resistance of sandstone. The pressure upon the top course ofthe towers on the Pittsburgh aqueduct, is over 9 tons for every superficial foot.

But it remains to be examined, in case a timber foundation, or piling, shouldbe resorted to, what degree of safety would be afforded by such a mode ofbuilding. It has been stated that the stratum of limestone, which, at low water,is exposed on the Covington side, is believed to extend all the way across to the