as possible, the only room for reduction was in the boilers. The Bureau therefore decided, after mature consideration, to advise that about three-fourths of the boiler-power should be put in the form of coil or tubulous boilers. The advantage of these boilers in point of lightness and rapidity of raising steam has long been appreciated, but a distrust of their durability and proper functioning when arranged in group has existed. While there are sufficient grounds for this feeling in the case of many boilers of this type, the Bureau is satisfied that there are some which will work well, and, as stated elsewhere, this will soon be determined by the Board on Coil Boilers.

The service which this vessel is to perform, coast defense, makes boilers of this type especially useful. Ordinarily she will be at anchor or under easy steam, the two cylindrical boilers which are to be fitted giving steam for ten knots speed. The emergency power in the coil boilers will enable steam to be raised in less than half an hour, in sufficient quantity to give seventeen knots.

If, as the Bureau anticipates, these boilers give entire satisfaction in practice, we shall be able to reduce the boiler weights for future ships almost one-half.

The two cylindrical boilers which are to be fitted are to work at 160 pounds, and are 11 feet

2 inches diameter by about 10 feet 7 inches long, the shell-plates being of mild steel inch thick. There will be two corrugated furnaces in each boiler, 42 inches diameter. Each boiler will have about 44 square feet of grate surface and about 1,420 square feet of heating surface. The material, size and arrangement of tubes is the same as already described for the Maine and the Monadnock.

As in the other vessels, evaporators will be fitted for supplying the distillers and replacing losses of fresh water. The evaporators are to have a capacity sufficient to supply in twentyfour hours the water necessary to fill the coil boilers.

Provision is made for heating the feed-water. The feed systems are the same as in the other vessels.

Cruisers 7 and 8, of 3,000 Tons Displacement.

These vessels are designed for a very high speed, and in consequence very powerful engines are needed to secure it. They are to be twin-screw, vertical, triple expansion engines of 10,000 I. H. P. at full power, when making 164 revolutions with 160 pounds pressure. The cylinders are 36, 53, and two of 57 inches diameter, by 33 inches stroke. Two low-pressure cylinders are fitted, because of the limited space athwartship, which would not have permitted a

good arrangement with a single large cylinder. Each engine is in a separate water-tight compartment. The piston-valves are all 20 inches diameter, there being one for each H. P. cylinder, two for each I. P. cylinder, and two for each L. P. cylinder. They are all worked from Stephenson double-bar links. Provision is made in these engines, as in all the Bureau's recent designs, for adjusting the point of cut-off for each cylinder independently of the others, by making the attachment of the suspension-rod of the link to the arm on reversing-shaft adjustable. The crank-shafts are in three sections, the two forward ones being interchangeable and the after ones reversible. The two L. P. cranks are placed opposite each other, as are the H. P. and Į. P. cranks, the plane of these two being at right angles to that of the two L. P. cranks. The journals are 131⁄2 inches diameter, and the crank-pins 141⁄2 inches diameter, all with 6-inch axial holes. The thrust shafts will be 13 inches diameter with 61⁄2-inch axial holes, and the propeller-shafts 134 inches diameter with 6% and 6-inch axial holes. The propellers will be three-bladed, of manganese bronze, or equivalent metal, and about 14 feet 6 inches diameter.

The condensers will be cylindrical, of composition, 5 feet 8 inches diameter, and the tubes II feet 6 inches long, each having a cooling surface of about 6,990 square feet. A valve is

fitted in the exhaust-pipes from L. P. cylinders to shut them off when the condenser is used for auxiliary purposes. Each centrifugal circulating pump will have a capacity of 9,000 gallons per minute when pumping from the bilge. There will be two vertical single-acting air-pumps for each condenser, 181⁄2 inches diameter and 161⁄2 inches stroke, worked by a compound engine.

There will be steam starting-valves, steamactuated throttle-valves, steam and hydraulic reversing-engine, turning-engine, workshop machinery, and the usual auxiliaries.

There will be four double-end and two singleend boilers of the usual return tubular type, all built of mild steel. Two of the double-end boilers will be 13 feet 4 inches diameter, and two 14 feet 61⁄2 inches diameter, all 20 feet 3% inches long. The single-end boilers will be 11 feet 6 inches diameter by 9 feet 10 inches long. The shell-plates will be 1 inches, I!! inches, and of an inch, respectively. The double-end boilers will each have six corrugated furnaces 44 inches diameter for the large, and 40 inches diameter for the small ones. The single-end boilers will each have two corrugated furnaces 42 inches diameter. The total grate surface is 607 square feet, and the total heating surface 20,167 square feet.

The size, material, and spacing of tubes are the same as for the Maine's boilers. The feed

systems are also like those of that ship.

The same arrangement of the evaporators for the various purposes exists as in the other ships, the capacity being 5,000 gallons of potable water per day.

Cruisers 9, 10 and 11, of 2,000 Tons Displace

ment.

The machinery for these vessels is, in its general features, a reduced copy of that for the 3,000-ton vessels, but each main engine has only one L. P. cylinder. The dimensions are as follows: Cylinders, 262, 39, and 63 inches diameter by 26 inches stroke. I. H. P. of main engines and air and circulating pumps at full power, 5,400, with 185 revolutions and 160 pounds pressure.

The piston-valves are one for the H. P. cylinder 14 inches diameter, one for I. P. cylinder 14 inches diameter, and two for L. P. cylinder 20 inches diameter.

The journals and pins of crank-shaft are 10 inches diameter with a 5-inch axial hole. The three sections are interchangeable, and the cranks are set 120° apart. The line and thrust shafts are 934 inches diameter with a 5-inch axial hole, and the propeller-shafts are 101⁄2 inches with a 6-inch axial hole.

The propellers will be four-bladed, about 11 feet diameter, and of manganese bronze or equivalent metal.