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The principle can be described in a single sentence. In the centre of the ship, and below the water line, there is fixed a kind of Turbine wheel, supplied with water through holes in the vessel's bottom, and which, being set in motion by an ordinary steam engine, revolves rapidly, and drives out a thick perpetual column of water through apertures, termed nozzles, on each side of the ship. This propelling power, unlike the paddle and screw, does not force the vessel ahead by pushing back the water, but acts directly on the vessel (something like the recoil produced by firing a gun), preventing of course that loss of power caused by every revolution of the paddle or screw. The allimportant agents, the nozzles, are the tubes through which the water is expelled from the wheel to the outlet apertures on the water line. When the steady stream is directed towards the stern the ship goes ahead; when to the stem, she backs; and when the streams flow one each way, the vessel, as if on a pivot, turns on her own length. These nozzles are so potent that they can be used to steer as well as to propel the ship; so that the smashing of a rudder would be a matter of perfect indifference. The advantage here is immense, when it is remembered how many disasters at sea have been traceable to the loss of a rudder, the breaking down of a paddle, or the fouling of a screw. In the Nautilus no portion of the machinery is exposed. If she were a ship of war, the invariable attempt of the enemy to shoot away paddles, screw, and rudder would be therefore useless; and if she were a merchantman, she would not labour under the disadvantage of paddles to diminish her sailing powers, or of that inevitable weakness of stern which attends the use of the screw. Again the leak, which in other ships too often means hopeless destruction, becomes here, if not a positive blessing, at least no source of danger or inconvenience, because the greedy wheel can be made to swallow up the dangerous water, use it to increase the speed of the vessel, and in doing so to send it out considerably faster than it came in. These are put forward as the main advantages; but it will at once be seen they would involve others, secondary perhaps to a certain extent, but still fraught with benefit. Thus the uniform working of the machinery prevents vibration, and consequent wear and tear; the pitching and rolling of a heavy sea produces none of that vexatious reaction which strains every part of the ship; the steamer leaves no swell and very little ferment behind; the peculiarity of the machinery enables the hull to be built on the lines of the best clipper ship that sails; and then there comes in the additional claim of economy, both in construction and working.

The Nautilus was tested with one of the ordinary iron paddle boats, and in the race down towards Gravesend she held her own, and once or twice got well ahead. The average speed was 11 miles an hour. It remains to be seen whether there is any limit to the application of this principle. Its success in vessels like those plying from bridge to bridge on the Thames was demonstrated without hitch or difficulty, and, so far as could be gathered from the trial, nothing can be better for river or canal navigation than boats propelled by this patent.

Shallow water seems to be no obstacle, and running aground is said to be an incident demanding very little anxiety. Most remarkable of all, by means of the nozzles, the vessel can be brought to a dead stop within half her own length, like a troop of cavalry charging a square. The time-honoured "call-boy" will find his occupation gone, for the ship can be stopped or her speed lessened by handles from a deck platform controlling the hydraulic propeller, and without the general vocal communications from or to the engine room. The Admiralty are so convinced of the fitness of the principle that they are now building a gunboat (the Waterwitch) at Blackwall, to be worked by the hydraulic propeller. This gunboat will be launched probably this month, and as she is to be of 778 tons burthen and 167 horse power, ber trial will in a measure decide a very important question as to the future of steamships.

The hydraulic propeller is not by any meaus a new invention, although its introduction on the Thames is comparatively recent. Like numerous other valuable inventions in shipbuilding, it came from beyond the Tweed. So far back as 1839, Mr. Ruthven, of Edinburgh, the patentee, began to theorise and adapt. He built models, improved them, exhibited them, got a patent for his principle, and for many years endured the usual difficulties arising from the ignorance and prejudice of indifferent or hostile persons. In 1851, a small vessel, 30 feet long, fitted up with the hydraulic propeller, was placed on the Thames, and a model 12 feet long was sent to the Great Exhibition. The jurors had nothing to say about in their report, but the inventor received considerable encouragement from practical men who saw the little craft on the Thames. In 1853, a ship, partly purchased by the Prussian government, was built for the Oder, upon which river she has been running ever since. The patent expired in 1863, and the Privy Council extended it for ten years. A good deal of most important evidence was given in favour of the invention before Lord Justice Knight Bruce on the application for renewal. The chief effort, however, to bring the invention fully and fairly before the public has been made in the building of the Nautilus, whose trial trip we have described. The public will have no difficulty in seeing her, as her owners invite the fullest inspection. At present, as we intimated, the Nautilus is not an exhibition ship, but a mere shell, fitted with two engines of 10-horse power each. She draws 2 feet of water, is 115 feet long, and being 7 feet 2 inches deep stands rather awkwardly high out of water. The hull closely resembles the Citizen boats, but being somewhat broader, deeper, and fuller in the lines, seems heavier. Having nothing but a temporary mast, or rather flagstaff, before the funnel, she looks conspicuously bare; but the main object-namely, the illustration of the principle-has been realised. Looked at from shore, the thick stream of water issuing from the nozzle may be seen shooting along close to the side like a white column of glass. It expends itself without causing much disturbance of the surrounding water.

Amongst the company were Admiral Elliott; Mr. Murray, chief

NO. 5.-VOL. XXXV.

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engineer of Portsmouth Dockyard; Mr. Steele, inspector of machinery to the Comptroller of the Navy; Captain Engledue, manager of the Thames Iron Works; Capt. Williams, Capt. Watts, Capt. Lovell, and Capt. Thomas, of the Peninsular and Oriental Steamship Company: Mr. Dudgeon, engineer to the Millwall Company (who are building the machinery for the Waterwitch); Mr. Hamilton, and Mr. Smith. We believe there will be an official Admiralty trial trip shortly.

American Monitors.

At a lecture recently delivered before the United Service Institute, Capt. Horton is reported to have said that "monitors are going out of favour in America,-in fact, most of them are now being turned into torpedoes;" the answer to which, without our desiring to enter controversially into the subject, may be found in the fact that every possible improvement and finish that engineering talent and the experiences of the late war can suggest are being put upon the latest monitors built, of the most powerful class of which, one, the Passaconaway, may be cited as an instance. This monitor is 345 feet long, 56 feet wide, and 18 feet 10 inches deep, 2,127 tons, and draws ready for sea 15 feet. She has two turrets, mounting each two 20-inch guns throwing 1,080 lbs. shot, with 15 inches thickness of wall (5 inches solid and 10 inches of laminated), and her side armour is 12 inches thick of solid plating. The most powerful engines yet constructed for monitors are being built for her, so that she shall attain an average speed of thirteen to fourteen knots. Sir Morton Peto also said, during a recent debate, that the monitors were not "sea-going" craft,-an assertion disproved almost daily in America by the outside passages made by monitors along the whole coast from Maine to New Orleans. Sir Morton evidently misunderstood or was misinformed on this point, probably owing to the fact that so far are Americans from looking with disfavour on the monitor system, as evidenced practically in our reply to Capt. Horton's remark, that many officers of their navy are not over-anxious to have their monitors too enthusiastically approved by other nations, from motives that are obvious.

It is conceded, we think, that excellence in a war ship depends on the possession of a number or all of the following properties, ranged in their order of value,-viz.: 1, speed; 2, sea-worthiness and quick manoeuvring power; 3, strength, and all possible simplicity of build, fitment, and machinery; 4, a battery, combining handiness for working with power and precision of projectile, whether large or small; 5, small target surface, little top-hamper, and steadiness or ease of motion in a seaway; 6, security from raking or vertical fire; 7, large capacity for coals and stores, and sufficiency of good quarters; 8, least draught for measurement; 9, durability; 10, recuperative power, or capacity for expedients in emergency. These qualities, singly and combined, form the means requisite to carry out, in such degree as they may exist, the two great principles of naval warfare; the primary one being power of attack, and the subordinate one power

for defence or escape when hopelessly overmatched. Without wishing to be understood as constituting ourselves the champions of the monitor system, we may with reason set forth the arguments of its partisans, among which, referring to our preceding scale of a man-ofwar's qualities, they claim as established facts, the possession by monitors of the following points:-1, strength, &c., of build; 2, capacity to carry with ease and work the heaviest ordnance yet made to better advantage than any other class of vessel; 3, little or no target surface, no top-hamper, and easy movement; 4, security from raking or vertical fire; 5, equal capacity for stores, &c., with broadside ships; 6, one-half the draught of water as compared with broadside ships throwing far less metal; 7, greater durability and less straining: making, out of the given ten points of requisite excellence, seven, claimed absolutely, and in some to a higher degree; while of the remaining three, the question of speed will eventually, with time and experience, so improve, as to be greater than that of ordinary ships, though even now their best monitors make 10 knots. Seaworthiness remains to be tested, and recuperative power, &c., will be solved by experiences now going on or in contemplation. But admitting the lack of these, they claim that monitors possess power of attack and power for defence so thoroughly, and to an extent so far surpassing any other description of ship, as by long odds to far overbalance any real or apparent defects as compared with broadside ships; and if it should be that in future naval battles the victory shall remain, as a rule, to the combatant who can show effective fighting front the longest while sustaining the least amount of injury or risk, then must preference be awarded to the monitor system. It is contended also, that on another point of no small consequence, that of relative less cost, monitors have the advantage, in the ratio of about one to five, over broadside ships throwing the same weight of metal. Viewed as mere constructions, "half-sunk rafts shut out from the light of heaven," as Mr. Reed terms them, or in whatever other disparaging sense, we hold all such considerations of mere taste or prejudice as totally beside the one great desideratum of ability to cope effectively and victoriously with a foe, in whatever more pleasing or accustomed form the latter might appear to the eye.

As regards comparative cost and numbers, some idea may be formed of the two systems by stating that for the 100,000 tons of iron-clad broadside ships composing her Majesty's navy, and which have cost over £8,000,000, there could have been put afloat a navy on the American plan composed thus:-50 two-turret monitors, and 20 swift cruisers of 2,500 tons, at £100,000 each, with 16 smaller swift ships of 1,500 tons, at £60,000 each; the whole fleet of 86 vessels throwing an aggregate maximum broadside of 100,000 lbs. against not certainly over 50,000 lbs. weight which our fleet of 30 iron-clads could combinedly throw; or, leaving the cruising ships out, the 50 monitors, armed with 400-pounders, would together give 80,000 lbs. at a single broadside. But, even admitting the possibility of the ironclads throwing as much metal, there would still remain the disparity

arising from 50 being opposed to 30 ships, of whatever sort they bethat is, nearly every single broadside ship could be engaged at the same time by two monitors, a disadvantage that will at once occur to any practical man who has ever seen a ship obliged to fight starboard and port batteries simultaneously for any time. The number of men would be for the 30 iron-clads somewhere about 15,000, while as each two-turret monitor requires only about 200 all told, 10,000 men would suffice for the whole fleet of the latter, or one-third less than the former,-a matter of no slight moment, considering the difficulty that frequently occurs of manning our ships.

In actual fighting experience, the monitors, if we may credit the official reports of the Unites States Government, have thus far satisfactorily achieved the work cut out for them, saving the foundering of one, and the destruction by torpedoes of some half-dozen others,— accidents from which no class of ships are exempt. As to the muchmooted question of why Charleston was not forced, materials for discussing the matter of a sufficiently precise nature are not yet before the world. But we may be permitted in the absence thereof to endorse the opinion held by more than one officer of experience, that in so far as the power to do so successfully existed before the besieged had leisure and opportunity to obstruct or command by shore batteries every possible approach past Fort Sumter, the monitor fleet could, and should, in conjunction with the land forces, under General Gillmore, have readily reduced the city. As it was, time was fruitlessly expended in bickerings until the whole thing became a very inferior repetition of Sir Charles Napier's feat in not taking Cronstadt by a coup de main. We, of course, are judging the matter from a mere engineering or warlike point of view, without at all wishing to enter into the question of right and wrong, as between Federals and Confederates, and are, as well, quite ready, on proper showing, to modify the opinion thus expressed. But until new and satisfactory light be thrown on the subject, we cannot but ascribe failure to men rather than to want of the proper means.

That monitors, in common with some other things emanating from America, are viewed disparagingly, as is the fact, does not speak well for the ingenuousness of opinion which should ever have precedence in matters of mere fact; but that such is the case in this instance we cannot in fairness deny, while utterly at a loss to discover any valid or worthy reason why such should be the case. It is more than probable that, as the oldest and strongest naval power on the globe, it may seem hard for us to swallow such a wholesale transformation, on a field we have made peculiarly our own, as is implied by substituting "rafts with cheese-boxes stuck upon them" for the noblelooking ships which may never again carry easy victory wherever they appear. Professional men of any branch are naturally loth to resign old ideas, albeit in favour of actual facts of newer date, and in nothing has this tenacity more perseveringly been shown than during the past ten years, in reference to our war navy. Had the strife been represented by blows instead of words, Whitehall would over and over

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