[Illustration: TYPICAL MASONRY AND EARTHWORK DAMS OF THE WORLD.]
The accompanying table gives the pressures to which various dams are subjected, and it may be noted with regard to the weight of water, generally assumed as 62.4 lb. per cubic foot, that it will, in some districts, in time of flood, carry so much matter in suspension as to be increased to as much as 75 lb. weight, or an addition of 20 per cent., which, it may be easily imagined, will affect the conditions of stability very seriously.
Lb. per sq. in. Gileppe (Verviers). 88 Furens (St. Etienne). 93 Puentes. 112 De Ban. 113 St. Chamond. 114 Alicante. 154 Hamiz (Algeria)--failed. 157 Habra (Algeria)--failed. 185
A diagram comparing the section derived from Molesworth's formula and those of Furens, Gileppe, Vyrnwy, and Quaker Bridge, is given at Fig. 20, the limit of pressure assumed for the masonry being 93 lb. per square inch, which is that of the Furens, the Gileppe being 88.
We illustrate the new dredger Ajax, recently built for Mr. Geo. F. Smith, of Stockton, Cal.
The dredger has now been working for two weeks at Wakefield, and, we are informed, is giving entire satisfaction; having been repeatedly timed to be discharging clay at the rate of 220 cubic yards per hour.
The Ajax is almost a duplicate of the last dredger designed by Mr. Ferris for levee building on Roberts Island, with such modifications and improvements as have suggested themselves in the two years it has been working.
The hull, oval in plan, is 36 ft. 10 in. by 60 ft. over all; it has four solid fore and aft bulkheads, and a well hole 5 × 12 ft. at one end for the bucket ladder.
The main engine is 10 × 24, operating, by bevel gearing and a 3½ in. vertical shaft, a 4 sided upper tumbler with 21 in. sides. This engine works also a gypsy shaft for swinging, and the conveyer that carries the mud ashore. A steam hoist with 6 × 11 engines raises and lowers the bucket ladder. The buckets, at 4 foot centers, have a struck capacity of 5 cubic feet, and are speeded to deliver from 18 to 20 a minute, according to the character of the material being handled. They are of boiler iron, with a 5 in. steel nosing. The links are of wrought iron, with cast bushings. The lower tumbler is hexagonal, on a 4 in. shaft.