NEW METHOD OF PRODUCING A MOST BEAUTIFUL ARTIFICIAL RAINBOW FOR THEATRICAL AND OTHER EXHIBITIONS.

Sir, I herewith send you a drawing and description of a new contrivance of mine for producing a prismatic rainbow of undeniable beauty and accuracy, and which will be found of great utility for theatrical exhibitions, when "heaven's aerial bow" is desired to be shown.

A box is first made of wood or tinplate, and of the form represented in the accompanying drawing. It is like a magic lantern, with this difference, that in the former neither lamp nor magnifying glasses are used, as in the latter. At C there is what may be termed a prismatic lens: it is a cone formed of flint-glass, made perfectly "true," and highly polished, and is fitted in the position shown in the figure. At D a circular hole is cut, so as to allow a portfire of brilliant-burning composition, B, to pass freely through; the latter ought to be of about of an inch in diameter. The portfire is first inflamed at the end B, and then pushed into the lantern; one of the size just mentioned will even give a greater illumination than an ordinary oxy-hydrogen light.

By the action of the lens C the light is decomposed into its component colours, which, when thrown on a flat surface, appear in all their distinct yet blended beauty. A circular-shaped spectrum will, of course, be formed; but half of it can be very easily concealed by placing the apparatus behind the cut scenery representing the hills, trees, &c., so as to cause the bow to be seen on the sky portion of the picture alone-one half of it

being thereby below the horizon, and hid from the spectator's view.

I have ofttimes thought that illumination portfires might also be used with some success in the magic lantern, screen microscope, &c., in lieu of the oxyhydrogen light apparatus, which is both expensive and cumbersome-large gasholders, &c., being requisite. Not that I think the latter plan will be effectually superseded in a hurry for large exhibitions, but that mine is more easily, conveniently, and cheaply put into action, and therefore more applicable for showing the objects in a private room : no apparatus for making the gases, nor any kind of instruments for using or collecting the same, being necessary.

The illumination portfires mentioned above are those usually sold at fireworkmakers, at from a penny to about sixpence each; one of a medium length will burn a sufficient time to show a single figure or object on the screen, and that with a most beautiful distinctness.

Sir, I am your very obedient servant,
Z. ROCKLINE.

Newcastle-on-Tyne, January 30, 1843.

COWELL'S PATENT TAPS.

Sir,-There are not many articles in daily use which cause so much and such varied annoyance, by their defectiveness, as taps.

The ordinary plug-tap is produced by turning, and made as accurate as practicable by grinding. If the grinding could be stopped when a satisfactory degree of accuracy had been attained, all might be well; but the fact is, that the very act of using the tap is but a continuation of the grinding process, which, being carried too far, is soon evidenced by leakage.

This mischievous effect has been attempted to be got over by resorting to tightening nuts, springs, and a host of other complicated contrivances; and expensive taps have thus been produced, which experience has shown to be little, if any thing, better, in point of durability and trustworthiness, than those of the older and simpler kind.

Repeated failures had invested this object with a most discouraging degree of hopelessness; the end in view has, however, at length been attained, and most successfully, by a very ingenious and

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On turning the screw in the one direction, the cross-head, links, and platform are depressed, which opens the aperture B, and allows the fluid to escape out through the nosel C. On reversing the screw, the platform D rises, and the metal round the orifice B, bedding upon the washer, makes a perfectly close joint.

The striking and important difference between the patent tap of Mr. Cowell and all previous contrivances for the like purpose consists in the action, or working parts of the former being altogether distinct and separate from the passage through which the fluid runs; no wear, therefore, however great, can affect the soundness of these taps, and, as the outlet is closed by screw pressure, they can never corrode or set fast. Another important advantage peculiar to Cowell's patent tap is, that, as the knob, or part which is struck when being driven into a barrel, is on a solid metal body, clear of the working parts, the latter remains uninjured, whatever number of blows may be given to the tap. The manufacturers of these taps, (Messrs. Stock and Sharp, of Birmingham,) have done ample justice to Mr. Cowell's ingenious invention, and at his suggestion they have adopted a woven fabric for the washers, in preference to leather; in boiler taps, and in other cases where great heat is present, this is highly important. The expansion by heat, which often operates so injuriously on other metal taps, produces no effect whatever on the patent tap, which continues both steam and water tight at all temperatures, and under all pressures.

If this tap has not realized absolute perfection, it has at least approximated so closely thereto, as to be sufficient for all practical purposes; and not the least of its merits is, that it is offered to the public at as reasonable a price as its imperfect predecessors. I remain, Sir, Yours respectfully,

29, Alfred-street, Islington,
March 7, 1843.

WM. BADDELEY.

the tap, and are moved up or down with the cross-head, by turning the male screw F.

This screw works in a female socket in the solid head of the tap, above the aperture through which the fluid passes.

PROGRESS OF SCREW-PROPELLING.

In our last notice on this subject (No. 1028, p. 336), the speed realized by the Government experimental steamer Bee, with Smith's propeller attached, in the trial in Long Reach, was stated by

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From this comparative statement it will be seen that Blaxland's screw not only gave the greatest speed with the least weight of material, but a speed which, all things considered, must be regarded as surpassing that of the paddle wheel. For though the trials were made under precisely the same circumstances, so far as the three screw-propellers were concerned, they had the following disadvantages in common, as compared with the paddle-wheel; namely, that they had to obtain their power from machinery which was made to be applied to sidepropellers only, and could not be adapted, without a certain loss of effect, to give motion to stern-propellers, and that while the screws were at work the vessel continued encumbered with the bulk and weight of the paddle-wheels, which were reefed only for the occasion (so to speak), not unshipped. The Blaxland propeller, therefore, having accomplished 7.115 miles, under such serious drawbacks, must be allowed to have done much more than the paddle-wheel, when it gave, with every circumstance in its favourvessel and machinery both specially adapted to it-7.7 miles.

Of the Mermaid, and Mr. Rennie's conoidal propeller, we have heard nothing farther than what is stated in the following paragraph, which we take, in a slightly abridged form, from the newspapers :

"The Mermaid' and her Screw Propeller.-On Tuesday se'nnight the Lords Commissioners of the Admiralty, attended by a numerous party of scientific gentlemen, met at Blackwall, and proceeded in the Mermaid, at a rapid rate to Woolwich, where her Majesty's steam-frigates, the Cyclops and Dee were waiting to receive them; their lordships then went on board the Cyclops, which immediately got under way, the Dee having preceded her a short time. After the Cyclops had advanced some dis

tance, the Mermaid was ordered to try her powers when she immediately quickened her speed, came forward, and rounded the Cyclops with the greatest facility she then continued down the river, passing the Dee in the same manner, and leaving the Cyclops two miles astern before she arrived at Northfleet. The Mermaid then turned back, and performed the measured mile at the rate, we are assured, of above thirteen miles through the water per hour. Some of their lordships then returned to London in the Cyclops; the remainder of the party proceeded on an official visit to Sheerness Dockyard, in the Mermaid. At a quarter past five they started again in the Mermaid, and reached the Brunswick-wharf, Blackwall, at eight o'clock, thus accomplishing the distance of 45 miles in two hours and three quarters."

It is but fair to Mr. Blaxland, Mr. Smith, and Captain Ericcson to observe that the efficiency of their respective propellers, as compared with Mr. Rennie's, is not to be judged of by the difference between the rates of speed which they realized when applied to the Bee, (7·115, 6·8, and 547 miles,) and those obtained by screw power in the Mermaid. In the same way that paddle-wheels, when applied to vessels of greater tonnage, better lines, and better engined than the Bee, have produced double the speed which was realized in the experiments made with that vessel in Long Reach, so may any of the propellers referred to, prove doubly effective when applied to a vessel made like the Mermaid, expressly for stern and sub-marine propulsion. We should like much to see what the Blaxland propeller would do if fitted to the Mermaid.

The chief difficulty which now remains to be overcome, in regard to screw propelling, relates to the means of transferring the power of the steam-engine to the propellers. In the Mermaid, Mr. Rennie first tried what could be accomplished by simple adhesion, as in the case of railways, but the result was an utter failure. Cog-wheel gearing was next had recourse to, and it is by means of this, the 12 and 13 miles an hour have been realized, but the noise and vibration attending the use of it are stated to be something "prodigious." Mr. Blaxland's band system of connexion is free from these objections, but then it is open to the no less serious one of extreme liability (as bands are now ordinarily made) to rapid wear, and sudden disruption. As we observed, however on a former occasion, (in effect if not in words,) we cannot bring ourselves to look on the production of a perfectly efficient band, as out of the range of mechanical possibility. We hold that

it is only necessary that it should be generally known that such a thing is wanted, in order to have the want of it speedily supplied.

We extract from the Liverpool Standard the following notice of something doing in the screw way on the Mersey, but we must confess that we are unable to collect from it, with sufficient distinctness, what the advantages are which Messrs. Mather, Dixon, and Grantham's propeller possesses over others.

"The Liverpool Screw."

"A small iron steam vessel has for some time been causing considerable interest on the river, and may be considered a subject of great public importance from the improvement which it exhibits over the present mode of applying steam power for the propulsion of vessels. *

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"It will be very generally known that the screw propeller has for some time excited considerable attention, from its causing the removal of paddle-wheels and boxes; but it has made but little progress in actual practice from two causes-one being the supposition that it could never be made so efficient in propelling as the paddle-wheeland the other that, to obtain sufficient velocity it was necessary that it should make more revolutions than the engines which worked it, requiring the intervention of spur wheels, or straps and pulleys. This small steam-vessel, which was built by Messrs. Mather, Dixon and Grantham, of this town, however, proves very clearly that such doubts are fallacious. The engines are applied direct to the shaft to which the screw is attached, and no spur wheels are required to obtain the necessary speed; and the makers have assured us that this principle can be carried out in the largest vessels without employing any means that practice has not already successfully established in the use of paddles on the old system. That high velocities can be attained is shown by this vessel, which has now beaten every steamer on the Mersey, and this with an expenditure of fuel not much exceeding one cwt. per hour.

"Another proof of the value of these improvements is shown in the fact, that the relative speed of the vessel and the screw are as 93 to 100, while with the paddle-wheel the proportion is generally as 70 to 100, showing a saving of upwards of 20 per cent., or, in other words, that an engine of 80 horses' power, with a screw, will drive a vessel as fast in smooth water as one of 100 horses', with paddle-wheels.

"The screw employed was patented by

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"The vessel is 65 feet between the perpendiculars, and 12 feet 6 inches beam; her average draft of water when ready for work is 3 feet 9 inches; she is worked by two cylinders 13 inches diameter, and 18 inches stroke, and, when light, averages about 85 revolutions per minute. The boiler is on the locomotive principle, and the usual pressure of the steam 50 lbs. per square inch, and is sometimes increased to 56 lbs. pansion valves are always used, which cut off the steam at one-fourth of the stroke-thus by making allowance for the pressure of the blast pipe, and for the operation of the expansion, which wire-draws the steam at closing, the actual power is equal only to a boiler pressure of from 27 lbs. to 30lbs. per square inch.

Ex

"In comparing this with the nominal horse-power of the vessels against which she has been running, which generally have a pressure of 7lbs. per square inch on the boiler, and 13lbs. in the condenser, (equal to a boiler pressure of 20lbs.) and the piston working 200 feet per minute, makes the power employed in the screw vessel from 19 to 21 horses.

"We may add a few particulars of a trip made by her on Friday last, which was taken in order to test her power of towing. She was matched against the Bridgewater, one of the best tow-boats on the river for her power. The Screw' had five flats, and the Bridgewater' seven.

"The nominal power of the former is 20, and of the latter is 34 horses. With these respective loads the screw-boat occupied 1 hour and 47 minutes from the Duke's Dock to the dock at Runcorn, beating the Bridgewater a few minutes-showing a superiority in the screw of about 25 per cent. in proportion to the nominal horse-power. But it has since been found from actual measurement that the respective power was as 163 to 300, showing a still greater advantage in favour of the screw.

"The little vessel, in a short time after her arrival at Runcorn, started for Weston Point. In the canals it is found that the screw has not the least effect on the banks, and that the disturbance in the water is no more than if the same vessel was tracked by

horses. At Weston Point, the canal being deep, the steamer could make more speed than is usually thought advisable in other places. She, however, took a flat in tow for nearly half the distance; and with this incumbrance, and the engine working slowly, she performed four miles in 36 minutes. An engineer belonging to the navigation accompanied her, and expressed himself satisfied that no injury to the banks could be caused by her.

"She then proceeded at full speed up the winding and beautiful River (Weaver,) and arrived, after a most delightful sail, at Northwich. Here she took on board a large party, and proceeded to Winsford, but, owing to the numerous narrow turns in the river, her speed could not be maintained. The next morning she returned to Weston Point, running the distance from Northwich in 2 hours and 25 minutes, including the delays in the locks.

"From this she started for Liverpool, the wind blowing very strongly against her, and the river very rough. Shortly after starting she overtook the Alice tow-boat, of 70 horsepower, with three flats in tow, one heavy and two light. Our little vessel took the loaded flat in tow, and now commenced a struggle. The short and angry sea continually breaking over the flats, and almost hiding them from the crew of the steamers; and here, more than ever, the triumphant superiority of the screw was shown. spite of the disturbed state of the water and the plunging of the vessels, it maintained its usual uniform speed, and soon left the Alice in the distance. On reaching Liverpool she again proceeded on her way and ran down the channel for some miles, but, as the tide was falling, the water became smooth, and she, therefore, returned to her moorings.

In

When she left the Duke's Dock on Friday, she had 18 cwt. of coke and 4 cwt. of coal on board; to this was added 11 cwt. of coke at Northwich; and with this fuel she performed all the work above described, and when she came to an anchor at 31 p.m. on Saturday, she had about 7 cwt. remaining. The steam was up from 7 a. m. on Friday, till 8 p. m. The fires were kept up all night, and at 6 a. m. on Saturday she again got up steam, and continued till 31 p. m. The quantity of fuel consumed was consequently very small.

EXTENSION OF PATENT RIGHT.

Judicial Committee of the Privy CouncilMay 13.

Petition of Lucena, assignee of patent granted to Elijah Galloway, for paddlewheels (commonly known as Morgan's). The SOLICITOR GENERAL and Mr. BUTT supported the petition; Mr. M. D. HILL and Mr. RICHARDS opposed it.

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This was an application for the extension of a patent, granted in 1829, for the wellknown paddle-wheel, known as Morgan's wheel," (see Mech. Mag., vol. xxii. No. 598.) From Mr. BUTT's statements it appeared that two patents (one for England, and the other for Scotland) had been granted to Elijah Galloway, in 1829, which were immediately after assigned by him to Mr. Wm. Morgan, who subsequently became a partner in the late firm of Acraman, Morgan, and Co., of Bristol, and was involved in their failure last year; having, however, some years previously-namely, in 1831, assigned one-fourth of his interest in the patent to Mr. Lucena, the petitioner, for 4,0007., and mortgaged the remainder, with some other securities, for 4,5007. In 1832, Mr. Morgan having become bankrupt, the whole title to the patent, by various mesne assignments, became vested in the petitioner. Up to 1835, the patent had only been applied to the Columbian, Firebrand, and other Government steamers. In that year the patent was infringed, in consequence of which proceedings ensued both at law and in equity, which did not terminate until 1839, and which entailed a loss of nearly 30007. on the petitioner. Mr. Morgan (who had the sole license) fitted up several vessels, principally for the Government, with the exception of some foreign vessels; but the patent had not been brought into general and public use, and the profits, therefore, which Mr. Lucena, the assignee, had derived from the invention, were very small, whilst he had sustained a loss of from 7000l. to 80007. The public were, however, beginning to appreciate its value, and it was about to be applied to the royal steam yacht, Victoria and Albert, now building.

Lords BROUGHAM and CAMPBELL expressed their surprise that, if its advantages were so great, the public should have been so slow in using it, for it appeared that none of the great steamers-the Atlantic steamers, for instance, which were fitted up without regard to expense-had adopted this paddlewheel.

Mr. BUTT said it had been suggested that there was some difficulty in keeping it in repair, in consequence of the frame being more complicated.