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leverage when at the greatest. former is consequent on a short stroke, and the latter, on a short connecting-rod. In carrying out the principle to an extreme, either jointly or separately, the same result takes place, namely, a total destruction of the whole mechanical energy by friction. On the other hand, let the long stroke and long connectingrod be extended to the utmost limits of man's capability, and we shall still have an engine that will work effectually, although the proportions be in an inverted form.

Having ventured to give an opinion on the principle which has for its basis the application of a short leverage with an increase of power to the purpose of driving paddle-wheels, I shall now proceed with a description of the accompanying drawings of the Haddington Engines, differently framed since they were presented to the notice of the Lords Commissioners of the Admiralty.

Fig. 1 is a plan; fig. 2, an end elevation, showing two engines connected by a single link; and fig. 3, a side elevation of one of them. a, plumber-block of crank-shaft; b, top of connecting-rod and-crank pin; c, crank; d, valve-case of cylinder; e, cylinder; f, steam-pipe; 9, air-pump; h, force-pump; i, levers for driving pumps, worked by the cross-head of the engine; j, condenser; and, hot-well. m, m, strong wood framing athwart the ship for supporting the plumber-blocks of paddle-shafts, (see figs. 1 and 2) and n, n, paddle-shafts. From this frame strong iron stays are extended to the cylinders; and in fig. 3, one is shown extended to the hot-well; 1, o, man-hole to cylinder; and p, the connecting link alluded to in the former part of this communication.

By this arrangement, the space occupied by the engine is reduced 46 per cent. in comparison with engines having side levers on the old plan, and the difference affords room for stowing about 100 tons of more coals in a vessel requiring engines of 200 horses power, and, as a matter of course, with vessels requiring engines of greater power, a similar advantage will be obtained. It might still be greater were the condenser, air-pump, and hot-well brought closer together, but the engine-room already is reduced to 17 feet 6 inches long, by 16 feet 10 inches wide, and it must not be forgotten that the

cylinders will throw off an equal quantity of radiating heat, and too much contraction would make the engine-room unhealthy.

If fig. 3, be turned upside down and the cylinder of the engine supposed to be fixed upon the floor of the vessel in the ordinary way, then by the plan before us, the connecting-rods b, at the same stage of construction as respects the moving parts, effect a rotary motion on the crank-shaft, which, with engines on the old plan, have only arrived at the length of vibrating the ends of two immense cast-iron lever beams; and these beams communicate the power to a third connecting rod, nearly as heavy as the other two; which, in its turn conveys the force to the crank shaft. By this comparison, the simplicity of the Haddington engines is made to appear most distinctly. Again, if the connecting rods b, be turned the reverse way, and the crank shaft supposed to be elevated a proper height to be driven by them, then the arrangement would be similar to that of a Gorgon engine, and the crank shaft 7 feet 6 inches higher than what it is; but this not being admissible in a steam vessel, the alternative heretofore explained has been adopted.

The connecting link p, offers an advantage to a steam frigate distinct from its accommodating nature as a mode of connection between two engines. For example, previous to an engagement, it may be removed in the short space of ten minutes; the paddle wheels would then be driven by their respective engines, and by giving the rudder of the ship power to act on the throttle-valves of the engines, the velocity of either paddle might be impeded to suit the movement of the vessel, which would give great facility in bringing her about. This, perhaps might be carrying the improvement too far, and the purpose might be answered equally well by the throttle-valves being operated on by hand from the deck. There can be no question about my engines working separately, as well as jointly, and by the plan suggested being adopted on such occasions, the danger of the one engine breaking down the other, in the event of a shot disabling either, would be avoided.

JAMES WHITE. 11, East-place, Lambeth, and Haddington, N.B. February, 1842.

A VIEW OF THE COMPARATIVE MERITS AND DEMERITS OF THE THREE DIFFERENT PLANS FOR THE PROPELLING OF STEAM- VESSELS, VIZ, PADDLE-WHEELS, THE ARCHIMEDEAN SCREW, AND A NEWLY-DISCOVERED PROPELLER.'

1. Paddle-wheels.

The Great Western steam-ship, of Bristol, has paddle-wheels of 28 feet diameter, making fifteen revolutions per minute, the same speed as the engines which make fifteen strokes per minute; so that this action will give a motion to the wheels of just 15 miles per hour, assisted by the wind and sails, or about 13 miles per hour without such assistance. The speed of the wheels, therefore, may be stated at just double that of the vessel, reckoned exclusively for that power belonging to the steam only, the average rate of speed across the Atlantic being about 9 miles per hour, inclusive of the wind and sails, and about 7 miles per hour exclusive thereof, although both together may be reckoned at 9 miles. Now, as the voyage to America is commonly made in about fourteen days, we have the following results:— 14 days 336 hours, and at the 9 miles per hour as an [average of speed,

=

3,024 miles

(assuming, of course, that the length of distance will admit of this estimation.) The engine power belonging to the vessel is about 500 horses power, with 7 feet length of stroke in the cylinder, and 15 strokes per minute, answering to the speed of the paddle-wheels. One revolution of the wheels will be 14 feet, and the engine motion being 15 times, as stated above, this gives a motion of 210 feet per minute, or 3 feet per second, for the piston travelling in the cylinder. Mr. Brunel says that this is, in fact, the actual rate of propulsion of the Great Western, and she is regarded as the most favoured paddle-wheel steamer that ever traversed the ocean.

2. The Screw.

The Archimedes vessel is furnished with a screw for its propeller, the dimensions of which are 5 ft. 9 in. diameter, and 8 feet horizontal length, having a motion given to it of 140 revolutions per minute, by 26 strokes of the engines. Assisted by the wind and sails, this power will only give a propulsive effect on the

The inventor of which may be communicated with by letter addressed to L., care of the publisher of the Mechanics' Magazine.

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vessel of about 10 miles per hour, derived from the motion given to the screw of about 28 miles per hour, which shows a propulsion of about, attended with a loss of about of that original motion. But taking off all the accelerated motion, both by machinery and the wind and sails, will, it is supposed, reduce the speed of 10 miles per hour down to 6 or 6 miles per hour, as that derived from the exclusive natural effect of the screw at the original speed of the engines of 26 strokes per minute.

Hence, the merits of the screw, on a comparison with paddle-wheels, stand at a much lower estimate, the screw losing of the original motion, whilst paddle-wheels only lose of their motion.

The Mechanics' Magazine states several defects belonging to the screw, that will always be an impediment to its competing with paddle-wheels, whether as regards utility, speed, power, or economy. The principal are

1. The monstrous friction, caused by the enormous speed of the screw.

2. Complexity of gear-work, rendered necessary for the high velocity.

3. The unfavourable action of the blade at the centre of motion, where it becomes parallel to the line of the ship. 3. The New Propeller.

Some time ago, a very limited, yet highly satisfactory experiment was made with this new propeller, at the West India Docks, in 24 feet depth of still water,-that piece of water having been selected as the most proper for making the trial in the fullest and fairest manner. The object was to ascertain the respective and comparative merits of the Archimedean screw propeller, as fixed to the Archimedes steam-vessel, and those of the new propeller.

"The motive power was obtained from a weight, permitted to descend through this 24 feet of still water, and propelling a model of each sort of propeller. The new propeller, made to a scale of 5 ft. 9 in. diameter, and only 4 ft. length, (just half that of the screw,) was by this weight propelled 12 feet distance in 15 seconds of time, whilst the screw could only propel 8 feet distance. Here was an advan

tage of half more space or speed in the same time.

But with the propeller made into 8 feet length, (instead of the 4 feet,) the additional engine power then wanted and required to convert the 10 miles into 15 miles per hour will constitute all the difference for that purpose; that is to say, the increased length of the propeller, by making it double, will give it double power and half more speed in the same time, as the propeller remains at the same speed of 12 miles per hour, as applied when of the 4 feet length.

A steam-vessel with this propeller will not, in short, require more, (if so much,) than about one-half engine power; the cost of fitting-up will therefore be proportionally less; it will be worked, also,

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Comparative View of Engine Power applied to the three several plans for the

propelling of vessels.

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Sir, I was sorry to find in your last Number (page 135) so disingenuous a reply from Mr. Emslie, who adheres to his own opinion with a pertinacity and inattention to facts, by no means creditable to his view of the question.

I would beg to assure Mr. Emslie, that my mind is left open for the unprejudiced consideration" of every plan that may be brought forward for the purpose of cleansing chimneys by mechanical means, whether it be the introduction of a principle entirely new, or-as in Mr. Emslie's case-the revival of an obsolete plan.

The question is one in practical domestic science in which I have felt considerable interest, and to which I have given some attention; at the same time, in reply to Mr. Emslie's insinuation, I beg to state, that the question is one in which, personally, I am altogether disinterested. I am by no means prepared

to say that Glass's is a perfect machine for the purpose, yet it is generally held to be decidedly the best hitherto produced. From a practical knowledge of what has been done, and also of what is now doing in this matter, I might stand upon my own opinion, yet in this case I am not left to do so. The vast superiority of Glass's machine has been established by many years' experience, to the satisfaction of the legislature, as well as of those gentlemen, who, from motives of the purest humanity undertook the emancipation of the "climbing-boys," and the introduction of the very best machine that could be found, without regard to any particular plans or individuals.

Like the master chimney-sweeps before

⚫ I say hitherto, because I am aware that a plan has recently been patented which professes to accomplish that to which Glass's machine cannot pretend, viz., to sweep chimneys having any number of right-angled turnings, without requiring the provision of any soot-doors.

IMPROVED MODIFICATION OF A NEW ELECTROTYPE PROCESS.

the House of Lords, Mr. Emslie has fabricated a drawing of such a chimney as the world never saw before-and to establish what? The superiority of the rope, weighted brush, and pulley system!

Mr. Emslie is peculiarly unfortunate in his "illustration," for he proves too much and thereby refutes his own argu ment. He admits (most truly) that the very outré chimney which he has sketched (and which never existed but on paper) cannot be swept by the rope and weighted brush alone, but requires in addition, a long-handled scraper! I shall not join issue with Mr. Emslie with respect to the comparative merits of brushes v. scrapers; both are excellent in their way; but as to the simplicity, efficiency, economy, and universality of application of the two systems-that is, of the "flexible rod,' and the now justly exploded "weightedbrush system," there can scarcely be a doubt in the mind of any impartial person as to which "has it."

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In reply to Mr. Emslie's question"Can a single flue be pointed out, which Glass's Machine is capable of cleansing, that the weighted-brush mode is not equally able to effect ?"-I reply, yes; a very great number. All flues having long horizontal passages, require a longhandled apparatus of some kind or other to effect the cleansing of the horizontal parts; the flexible jointed rods of Mr. Glass are better adapted for this purpose than any thing else-whether they be equipped with a brush or a scraper. The weighted brush alone cannot, under any circumstances, cleanse the horizontal parts of chimneys, but must have a Glass's machine, (or something equivalent,) to act in conjunction with it; Glass's machine, then, may as well do the whole, and the weighted brush go to

"the tomb of all the Capulets." The idea of having two distinct machines to perform an operation which one of them the essential one-is capable of performing alone, is preposterous.

I will not trouble you to engrave any sketches of the kind of chimneys referred to, as your readers will find them ready to their hands in Mr. Stevens's little pamphlet.*

Mr. M'Gillivray's suggestion for im

Plain Hints on the Subject of Chimney-sweeping. To be had gratis at the Hand-in-Hand Insurance-office, Bridge-street, London.

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Sir,-A discovery has been recently made of etching copper plates, by first gilding them by the electrotype, and then delineating the drawing through the coat of gold to the copper. I tried the gilding process several times, but could not succeed in producing a firm coat of metal; and I am acquainted with many scientific gentlemen who arrived at the same result, namely, a dirty black powder easily rubbed off, instead of the "glittering metallic surface of incomparable beauty" as it has been designated by some. deed I am half inclined to doubt that such a thing has ever been accomplished. My trials with the "noble" metals, proving in every case a decided failure, I thought of trying what could be done by means of the cupreous deposit, as I always found it perfectly pure and firm, provided only, care were taken in conducting the process. My first experiment proved quite successful; the subject of it was an ordinary steel plate: I covered it with a thin film of copper, which I afterwards etched, and bit up with dilute sulphuric acid. Far finer and closer lines can be formed on this ground than on that in general use at present, which arises from the latter being required to be laid comparatively thicker on, which, together with its property of adhering to the point of the tool during the process, sometimes sends a whole body of fine line-work into a broken unineaning mass. What I consider the greatest advantage attending working on a metallic "ground," is, that after the effect, &c. is bit in, the plate can again undergo the same process, if the resulting etching be not satisfactory-an object not to be attained by the employment of grounds of a waxy or resinous nature. Such grounds always require to be totally removed before the picture can be pronounced

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Sir,-Expecting to be engaged in a situation, about three months ago, where there would necessarily be a great deal of travelling, and the income hardly sufficient to cover the expense of keeping a horse, over and above other expenditures, I applied myself to devise some method whereby I might travel with more ease and facility, than I could possibly do without some combination of art with nature. The following is the result of my cogitations, which I shall feel obliged by your submitting to your numerous readers, in order that any deficiency in the principle may be pointed out, for the benefit of mankind generally, and your humble servant in particular, as I intend to fit up such a machine, with the expectation of its being really useful.

A is one of two large light wheels, 8 feet in diameter, (which is the largest size, according to Professor Babbage, that can be rendered useful for such purposes;) B is a guide-wheel, about 3 feet; CC is the body, or fixed frame of the carriage, made of wrought iron, and ast light as possible: there may either be a seat for two persons, and a packing box or boot underneath; or, if designed for one traveller alone, it may merely be a platform case covered with loose oilcloth, to carry his food or any small article in. DD are the propellers, worked by the opposite cranks F, (on the same shaft,) and sliding freely up and down in self-adjusting guide-sockets, hung each on its own axis in the moveable frame E, which, when placed in the

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