We are glad to find that we are at length advancing, instead of retrograding in the experiments which are daily being made in the application of screw machinery to vessels of war. The progress has been of late, as it ought to be, a gradual development of the excellence of a novel power of propulsion, and what has been attempted step by step has been secured, and will form an invaluable data for working out the same perfection in screw-steaming as has been attained in the use of the paddle-wheel. This must be a source of congratulation to all who have of late years been accustomed to see so many hundreds of thousands of the public money thrown away on useless and absurd unscientific experiments.

We have at last some satisfaction in expenditure - some encouragement from the past to hope for the future. We have emerged from gross and expensive blundering and conceited empiricism into something like a clear and defined course, pursuing which carefully, steadily, and economically, supported by sound theory, guided by practice and warned by experience, we may justly anticipate results of an important and valuable character. It is impossible to estimate too highly what was commenced in the Amphion, now at Spithead ; to this vessel was applied the first great scheme of auxiliary propulsion by means of screw - the ship, it being remembered, not adapted for the purpose, for which she was appropriated, but selected to try 300 horse power screw machinery on Count Rosen's principle.

The pains which have been taken by various parties to work out the knotty problem of success in this vessel are beyond all pecuniary reward or even appreciation, especially when it is known that the prejudices of Naval officers, as well as engineers, who certainly ought to have known better, or to have been more liberal, were perhaps more difficult to be allayed or dissipated than even the working of the machinery itself. To the honour and credit of Mr. Miller, however, the senior of the firm of Miller Ravenhill, and Co., who manufactured and matured the engines, and who, although in very bad health, did not hesitate to endure all the miseries of an ill conditioned man-of-war to superintend the experiments on board the Amphion ; to Mr. F. F. Smith, the projector of the screw propeller ; and last, but not least, to Mr. Dinnen, inspector of steam machinery afloat, and who established the success of the experiments, the everlasting gratitude of the scientific world, and the thanks of the government are most justly due.

They were the pioneers in this great work, and the Amphion is the ship that has laid the foundation for that mighty success which is shadowed forth in the working of the Encounter sloop, the second large ship which has been. tried with advantage and credit. In our former notices of the Encounter, we have stated that she was designed by Mr. Fincham, of Portsmouth Dockyard. She is 895 tons, and has engines of 360 horse power, by Messrs. Penn and Co., and we then spoke of the compactness of the machinery. and the rate of her speed on the passage to Portsmouth from Woolwich. This vessel is, indeed, a wonderful instance of what has been accomplished in the improvement of both vessel and engines. She was tried several times on the river with the most gratifying results. On the last trial in the river, immersed with weights equal to her stores and armament, she attained an average speed of 11 knots, the engines having cylinders 60 inches diameter, with a stroke of 2 feet 3 inches, making 78 revolutions, with a screw of 12 feet 6 in diameter, and 16 feet pitch : and this speed with another and better adapted screw. she has maintained within half a knot on a sea passage, the ship too, having comparatively for a steamer, a bluff bow, as is necessary for men-of-war to possess.

A third large ship is now about to come into the field of experiment, and this vessel is the frigate Dauntless. She was built by the same naval architect (Fincham), but that extreme portion of her stern in which the propeller is placed, instead of being finely shaped away as that of the Encounter, is square, and thus in her case it is proved beyond question, that with a square truck, although with lines generally good and well adapted for a screw-steamer, she cannot attain that speed which the Encounter with a finer run has acquired ; for although the Dauntless has engines of 580 horse-power to 1496 tons, or 1 to 2.58, the highest mean rate of speed on trial was not beyond 7� knots. We have accounted for the difference between this vessel and the Encounter to some extent ; but it will be a subject of inquiry, whether or not the description of engine has not likewise something to do with the results.

We may repeat, however, with this short notice of screw steam-vessels, that we seem at length to be progressing in a satisfactory manner, and to acquire grounds for continuing our experiments to the attainment of that perfection in steam-machinery for vessels adapted for war purposes, which it is so desirable for this country to possess.

The Reynard, screw schooner, is not vet commissioned by Commander Cracroft. Her engines, we hear, are fitted with much compactness by Messrs. Rennie, whilst many improvements suggested by Mr. Humphries, the superintendent of their factory, have added much to their completeness By an ingenious contrivance of Mr. Humphries, the screw propeller is lifted out of its position with the greatest facility, at the will of the engineer in the engine-room. On the last trial the time occupied in lifting the screw-rudder three feet out of the water was two and a-half minutes, and on one occasion one and a-half minutes. The engine was stopped and disconnected, and the screw was lifted out of the water in the space of five minutes ; and it was lowered, the engines connected, and the machinery in motion again in an equally short apace. The vibration, it is reported, is not perceptible, and the chimney can be lowered and berthed in five minutes. Morning Herald.

SG & SGTL ; Vol 5 ; pages 311-2.

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