The twin screw dredger Dolphin was recently constructed for the Colonies, under the direction of Sir John Coode, assisted by Mr. Wm. Matthews, C.E., and is especially designed, says the _Engineer_, for harbor improvements in the West Indies. The dimensions are: Ft. In. Length between perpendiculars 130 0 Breadth moulded 30 0 Depth 8 0 ENGINES--Compound surface condensing, I.H.P 250 Stroke of pumps 14 Diameter of high pressure cylinder 16½ " low pressure " 33 Length of stroke 24 Diameter of air pump 11½ " circulating pump 6½ " feed pumps 2½ " bilge pumps 2½ The boiler is of steel, for a working pressure of 90 lb. per square inch. The bucket ladder works through a well formed in the center of the vessel, and dredges to a depth of 33 ft. below the water level, and the buckets are made wholly of steel, and are capable of lifting 250 tons of free soil per hour. Triple-geared winches are supplied at bow and stern for working the mooring chains, the barrels of which can be worked independently or conjointly, as required. The cabins for the officers and crew are of the most complete description; those of the former being fitted on starboard side of the well, and consist of rooms for the captain, mate, and engineers, also mess room. All the rooms are large and efficiently lighted and ventilated. A powerful crane is erected at forward end for overhauling the buckets, hoisting gear, etc. [Illustration: THE DREDGER DOLPHIN.] Hydraulic Dredging at Washington. At a recent meeting of the Engineers' Club of Philadelphia, a paper by Conway B. Hunt was read on hydraulic dredging machinery. The paper mentions the early application of the principle of hydraulic dredging, that is, the mixing of dredged material with water and then removing the mixture by suction or otherwise; and after referring briefly to the Roy Stone and Bowers dredges as typical machines, describes in detail the Von Schmidt dredge. Two of these dredges are engaged on the improvement of the Potomac River at Washington, D. C., under the United States Government. Each is 100 feet by 50 feet, with a semicircular bow, around which travels a vertical suction pipe, 22 in. in diameter, and telescopic. At its foot is a conical hood, beneath which works a rotary excavating plow, 8 feet in diameter. The suction is produced by a powerful centrifugal pump, run by a 200 horse power engine.