engines on board the Amethyst is passed into the low-pressure turbine receiver instead of into the condenser-a practice carried out in the other ships. At 14 knots the conditions are, so far as economy is concerned, more equal; but when the speed was increased to 18 knots it was found that the consumption on board the Amethyst was something like 20 per cent less. At 20 knots it was nearly 30 per cent less, and at the higher speed improvement was still greater. The influence of this economy on the radius of action is very marked. For instance, the turbine-propelled ship could, with her 750 tons of coal on board, steam 3,160 sea miles at 20 knots, as compared with 2,140 miles by the cruisers fitted with the ordinary machinery.

Turning now to the details which we have collated from these respective vessels, we may note, first, that the Amethyst, the vessel supplied with steam turbines by the Parsons Marine Steam Turbine Company (Limited), of Wallsend-on-Tyne, was constructed by Sir W. G. Armstrong, Whitworth & Co. (Limited), at the Elswick Works. The other three ships are the Sapphire, constructed_and engined by the Palmers Shipbuilding and Iron Company (Limited), and the Topaz and Diamond, constructed and engined by Messrs. Laird, Cammell & Co. at their Birkenhead works. So far as the hull is concerned, all four vessels are alike. With a length of 360 feet and a beam of 40 feet, they displace 3,000 tons when the draft is 14 feet 6 inches. In all of the trials this draft was either equaled or slightly exceeded. They are third-class cruisers, and will probably be used for dispatch work, although the speed of the Amethyst may justify her being regarded as a scout. The armament includes twelve 4-inch guns, one on the poop, a bow chaser on the forecastle, and five on each broadside on the upper deck. These guns have hoods of 4-inch armor. In addition there are eight 3-pounders, three Maxim guns, and two torpedo-launching tubes on the upper deck.

The boilers are of the Express water-tube type, and it was specified that the coal burnt per square foot of heating surface should not exceed 1 pound. In the Amethyst the Yarrow boiler, as constructed by Messrs. Hawthorn, Leslie & Co., has been adopted, the fire-grate area being 493.5 square feet and the heating surface 25,968 square feet, a ratio of 1:52.5. In these boilers the constructors have again utilized the method of adopting the two outer rows of tubes for heating the feed water. The top of the water drum to which these tubes are connected is isolated by a diaphragm plate from the remainder of the drum, and into this space the feed water is discharged. This is an important subject in turbine driving, because, owing to the fact that a high vacuum is desiderated, it results that the temperature of the feed water is less than in other ships by about 20° F. The effect of the utilization of these two outer tubes is to heat the water without adding materially to weight carried-always an important matter in war-ship designs. The Amethyst tubes are 14 inches in diameter. The Laird-Normand boilers fitted to the Topaz and Diamond have 15-inch tubes, but in the Reed boilers in the Sapphire the tubes are of 1-inch diameter.

In all cases the two rows nearest the fire are greater in internal diameter to the extent of one-fourth of an inch. The boilers are arranged in all the ships two in the forward stokehole and four in each of the other two. All the 10 boilers are single-ended and placed back to back. In each ship the stokehole is closed, the fans being driven

by inclosed steam engines arranged for forced lubrication. The air pressures on the full-power trial in the reciprocating-engined ship ranged from 1.7 to 2.6 inches. In the Amethyst, on the other hand, the pressure at full power was 1.7 inches on one trial and 1.6 inches on another. The former was run in very rough weather, when the force of the wind was four to six, and the other on Wednesday of this week with a calm sea. In Table 1, page 690, where the results of all the trials of the Amethyst are set out in detail, it will be noted that at lower power the high air pressure of 1.9 inches is recorded. This is explained by the fact that only four of the boilers were used. In the other trials the pressure was normal. The summary of boiler performances in Table 3 shows the result of the higher air pressure, and also indicates how easily the Amethyst attained her excess in speed.

The reciprocating engines on the two Laird cruisers and on the one Palmer ship are distinctly suggestive of the destroyer type, having at back and front forged steel columns, braced diagonally. The scantlings are heavier and the working parts are more substantial generally, while the number of revolutions is considerably less. The high-pressure cylinders are 244 inches in diameter, the intermediate cylinders 38 inches, and the two low-pressure cylinders 42 inches in diameter, the stroke being 24 inches. It was anticipated that the full power of 9,800 indicated horsepower would be developed when the machinery was making 250 revolutions, equal to a piston speed of 1,000 feet per minute. In the case of the Topaz the air pumps are worked off the main engine. This was the first of the vessels laid down, and subsequent to the order being placed, it was decided that in the others separate air pumps should be utilized, consistent with later-day practice, adopted in view of the better vacuum obtainable by this method. The auxiliary machinery includes two electriclighting forced-lubrication engines, the dynamos being of 350 amperes capacity at 150 volts, when the engines are making 450 revolutions per minute; two evaporators, capable of evaporating 60 tons per day; and two distilling condensers, capable of condensing steam from the evaporators at the rate of 20 tons per day, in addition to the usual donkey and other pumps.

TABLE I.-Results of steam trials of H. M. S. Amethyst with Parson's steam turbines.

Date of trial.

Duration of trial.

Draught of water (mean).
Speed of ship.

Air pressure in stokeholds.
Steam pressure in boilers
Steam pressure in receivers:
Cruising H. P

August 1 and 2,1904.

24 hours at 10

3, 1904.

July 12 and

13, 1904.

271

276.

Number of boilers in use