In Ramsbottom's Duplex hammer, shown in fig. 52, two horizontal hammers running upon wheels are advanced and retired by a sort of elbow-jointed lever worked by a steam cylinder set beneath the floor. But in some cases a cylinder is set behind each

THWAITES AND CARBUTT'S DOUBLE CYLINDER STEAM HAMMER
(ANOTHER FORM).

hammer to press it forward, and the action of the two is rendered synchronous by the interposition of a coarse right and left hand screw which rotates as the hammers advance and retire. All things considered, however, a hydraulic squeezer is certainly better than any form of hammer as it will better enable the pressure to be transmitted to the heart

of the iron, and will give time for the slag to escape.

In illustrating the special features of the various forms of marine engines of modern construction, the most convenient course will be to take an example of an engine by each principal maker, and to describe its structure and peculiarities. A tolerably just conception will thus be arrived at of the present condition of marine engineering in this country in its most perfect form, care being taken that the examples selected are good and recent examples of their several kinds.

Boulton and Watt.-The example of modern engines by these makers that I shall select is the oscillating paddle engines of the Holyhead steamers, Ulster

and Munster; for although I might have selected a still more recent example, I could not have selected a more perfect one. These vessels have now been plying regularly across the Channel at all seasons for a sufficient time thoroughly to test their qualities, and they have been found to maintain a very high speed and to work in a most satisfactory manner. The vessels are each 328 ft. long, with 35 ft. breadth beam, 21 ft. depth of hold, and they each measure about 2,000 tons, builder's measurement. Each vessel is propelled by two oscillating engines of 96 in. diameter of cylinder, and 7 ft. stroke. The pressure of steam in the boiler is 26 lbs. per sq. in. The nominal power of each pair of engines by the Admiralty rule is 750 horses. They make 23 strokes per minute, and they work up to 4,100 actual or indicated horses' power.

The boilers are tubular boilers with iron tubes; they are made in eight parts, and contain in all 48 furnaces. The total heating surface of the boiler is 18,400 sq. feet, and the total area of grate bars is 840 sq. ft. The area of the immersed midship section of the vessel is 350 sq. ft. and the coefficient of performance 860. The draught of water of each of the vessels when launched was: forward, 9 ft. 3 in.; and aft, 8 ft. 2 in. The draught of water with the engines, boilers, masts, and fittings, on board, but without water in the boilers, was, forward, 12 ft., and aft, 12 ft. 6 in. The draught of water when ready for sea, and complete with stores, and 75 tons of

ft. diameter

coals, was, forward, 13 ft., and aft, 13 ft. 4 in. The weight of the engines is 220 tons, of the boilers 230 tons, of the water in the boilers, 170 tons, and of the paddle wheels, 110 tons: making a total weight of 730 tons, or nearly 1 ton per nominal horse power. The pistons are each made with a metallic ring pressed out by springs. The average pressure on the piston is 28.77 lbs. per sq. in. The total number of tubes in the boilers is 4,240, of 21 in. diameter, 5 ft. 3 in. long, and th thick. The tube plates are of ironin. thick, and the tubes are 14 in. distant from each other. The length of each furnace is 7 ft., and its breadth 2 ft. There are two sets of boilers in each vessel, one before and the other behind the engines, and each set has a chimney 7 and 44 ft. high above the grates. wheels are feathering, 33 ft. inner edge of the outer ring. each wheel, and each float is 4 ft. deep and 12 ft. long. The dip of the wheels is 5 ft. 9 in. at deep draught. The steam is superheated by passing up and down through annular steam chests surrounding the chimneys, divisions being introduced into the annular space to compel the steam to ascend and descend before escaping to the steam pipe, as in the arrangement which was introduced by me into the Don Juan steamer as far back as 1837. These vessels, and two similar vessels, the Leinster and Connaught, the engines of which were constructed by Messrs. Ravenhill, Salkeld and Co., have realised a

The paddle

9 in. diameter to the There are 14 floats in

speed of upwards of 20 miles an hour, and an average speed in all weathers, during the first six winter months, of 18 miles an hour. In the Leinster and Connaught the cylinders are 98 in. diameter, and 6 ft. 6 in. stroke, and the engines are rated at 720 nominal horses' power, but are in reality 770 nominal horses' power. There are eight boilers, containing 40 furnaces and 4,176 tubes, and a total heating surface of 16,800 sq. ft. At the official trial the engines, with a pressure of steam of 20 lbs., made from 25 to 26 revolutions per minute, and exerted 4,751 actual horses' power. The consumption of fuel is about 3 lbs. per indicated horse power per hour.

John Penn and Son.-The engines of these makers which I shall select for illustration are the engines of the Warrior, Black Prince, and Achilles-all horizontal trunk engines of the construction represented at page 79 of my 'Catechism of the Steam Engine.'

These engines are each of 1,250 horse power, and notwithstanding their immense size, they are distinguished by the same beauty and accuracy of workmanship for which Messrs. Penn's engines have long been famous. The cylinders are of 112 in. in diameter, and 4 ft. stroke. The trunks are of 41 in. diameter, which reduces the effective diameter of the cylinders to 104 in. The air pumps are double acting, 36 in. diameter, and 4 ft. stroke. The feed and bilge pumps are 7 in. diameter; the crank shaft is of 19 in. diameter, and the screw shafting is of 17 in. diameter. The screw, which is on Griffith's plan, is 24 ft.