WATER-WHEELS. COWAN'S GAS METER. Smeaton concluded that the overshot water-wheel realized but sixty-six per cent. of the theoretical power of the water. The Franklin Institute has shown that, when accurately constructed, "eighty-four per cent. of the power expended may be relied on for the effect." Smeaton also concluded from his experiments that "the best velocity (for an overshot wheel) is a little more than three feet" at the skirt-though, singularly enough, he used a much higher speed in his practice, and yet never formally corrected the statements he had made before the Royal Society. The Franklin Institute has shown, that "the best velocity" ranges from "four and a half to six and an eighth, and probably even to seven and a half feet per second."-The Franklin Journal. ATMOSPHERIC ENGINES: THE "SAPPHIRE." Sir,-Your correspondent "Curve," in his reply to the queries of a Steam-boat Proprietor, has pointed out the disadvantages of several varieties of steam-engines constructed on Watt's principles, in comparison with the atmospheric engines of the Sapphire, and has remarked, that the economy of Boulton and Watt's engines does not depend on the use of the cylinder cover, but on the employment of the mode patented by Watt of condensation in a separate vessel. Has not Watt's condenser been applied to the open topped cylinders of the "Sapphire," and should not such engines be termed "Watt's Atmospheric," to distinguish them from Newcomen's, or the old atmospheric, in which condensation was effected in the working cylinder? The views of your correspondent respecting the friction of these engines seem liable to objection, and it would perhaps be safer, in the absence of good practical data, to assume friction as proportional rather to the power exerted, than to the area of rubbing surface alone. Possibly low steam may require its packing to be less tight in a higher ratio than the increase of area for equal power; if the differences are appreciable, the chances seem to me to be in favour of low steam. The escape of heat, in the case of an open-topped cylinder, is an obvious defect, both as a direct source of waste, and as producing an injurious effect. I should be obliged for information on this point:Whether it has not been overrated in theory? And whether, in practice, the heat of the 319 engine-room is much higher than usual in the Sapphire? The common opinion referred to in the queries, that" atmospheric engines must be larger, and consequently heavier, than engines of equal nominal power on the usual plan, besides being less economical in work. ing than the double-acting engines of Mr. Watt," must be derived from tradition, as until the Sapphire's performances were before the world, no data for opinions, I apprehend, existed. Perhaps the opinion equally prevalent of the necessity of using only low steam in atmospheric engines is based on no better foundation. It may be asked, Why might not the piston of an atmospheric engine be loaded to from 7lbs. to 15lbs. per square inch? High steam could then be admitted to work either at full pressure or expansively in the cylinder, to drive up the weight against atmospheric pressure, when the down-stroke would be performed by the weight and atmosphere conjointly. A scheme of this nature seems better adapted for a pumping than a marine engine, and I propose to forward, for subsequent insertion, three modes in which it may be carried out in Watts's atmospheric engine. The success of the Sapphire's engines have pointed out a course that could have been adopted by Watt, in the introduction of his steam engine improvements, by means of which the early commercial difficulties of the firm might perhaps have been avoided. The reasons against this course, I apprehend, have been recorded by Smeaton; since that period atmospheric engines have been neglected. Their real position in the scale of merit arising from the economy of their construction, and their probable greater durability, is a subject of interest to many parties. The present ideas of atmospheric engines refer to Newcomen's engine alone; but the present question is between Watt's atmospheric and Watt's steam-pressure engines, and the different conditions best suited for each variety. I remain, yours faithfully, May 6, 1844. COWAN'S GAS METER. S. Sir,-When looking over the pages of No. 1071 of your Magazine for February 17, I found on page 77, diagrams of Mr. Cowan's improved gas-meter drum, and on the next page a description of the same, in which it is stated, that gas is measured by this drum, with as much precision as spirits are by the standard measure. Now, Sir, had I not met with this, I should, in all probability, never have informed you that I made a drum on this principle near five years ago, and had I not known that, even with this improvement, it was imperfect, it would, in all probability, have been before the public at least four years ago. In the common drum there is a certain amount of error in each revolution, which is caused by increasing or decreasing the quantity of water above or below the proper standard. But this error is brought about in two ways, or in two parts of the drum, namely, partly by increasing or decreasing the capacity of the gas-chamber in the body of the drum, and partly by increasing or decreasing the capacity of that part of the outlet which is above the surface of the water when the chamber is closed by the water at the inlet side. The improvement of Mr. Cowan has the effect of keeping the capacity of the chamber in the body of the drum constant, but the inlet and outlet are altered by the variations of the water as in the common drum; for if the water be lowered half an inch below the proper line, the drum must be turned half an inch upon its axis before the inlet can be closed, which will make an inch difference in the outlet. Now, this will make at least an error of four cubic inches of gas for each revolution of the drum. I am, Sir, yours, &c. Preston, April 17, 1844. J. CHETWIN. NOTES AND NOTICES. The "City of London Steamer."-On the 18th ult., a magnificent iron steamer, to which this name has been given, was launched from the new buildingyard of Mr. Robert Napier, at Govan, near Glasgow. She belongs to the rich and enterprising Aberdeen Steam Packet Company, and it is intended that she should ply between that prosperous city and London. She measures, from stem to stern, upwards of 230 feet; breadth of beam, 31 feet; depth of hold, 20 feet; estimated burthen, 1100 tons. Hungerford Suspension-bridge.-Casual spectators, unacquainted with the art of building suspensionbridges, when they only observe two large masses of masonry erected about 100 yards from each bank of the Thames, with no communication either from the shore or with each other, can little imagine that the structure is so near its completion, that during the present summer the public will be enabled to cross from Hungerford-market to the Belvidereroad, Lambeth, for the small toll of one farthing each. To the curious this bridge is worth notice, as being the only one in the metropolis dedicated to foot passengers alone, and erected on the principle of suspension. The entire length of the bridge suspended on chains will be 1,342 feet 6 inches-that is, the centre span or arch, 676 feet 6 inches; those on the side 333 feet each. The width within the chains will be 14 feet, and a clear pathway of 13 feet; the height of the flooring above high water (Trinity standard), in the centre 31 feet 6 inches, at each pier 28 feet 6 inches, and at each abutment 22 feet 6 inches; the height of each pier above the flooring 55 feet 3 inches; the number of main plates which form the chain is 2,500, about 24 feet each in length. The total weight of iron is between 700 and 800 tons, and the estimated cost, including the approaches, is 110,000l. It will be seen that its centre span alone is nearly 100 feet greater than the entire of the deservedly celebrated Menai-bridge, which is 579 feet 10 inches. It is likewise 274 feet greater than the centre span of Hammersmithbridge, which is 402 feet 3 inches; and above three times as great as the centre arch of Southwarkbridge, at present the largest in London. Indeed, with the exception of the wire bridge at Fribourg, in Switzerland, which is 870 feet, it will be by far the largest in existence.-Mining Journal. Glass Milk Pans.-Captain Stanley Carr, of Tüsehenbeck, near Lubeck, has transmitted to the Royal Agricultural Society of England, a glass milk pan, employed successfully in his German dairy. From the memoir which accompanies the glass pan, it appears to be everything that can be desired in a dairy, more easily cleaned than wood, and in Germany cheaper than copper tinned, or cast iron enamelled; but the excise on glass renders their use in this country quite out of the question. The specimen sent by Captain Carr, is 16 inches broad at the top, and 12 inches at the bottom, the glass dark bottle green, perfectly smooth, and about one-eighth of an inch thick, and provided with a rounded rim, which makes it easy to retain a safe hold of them when full. It contains eight quarts, but it is not usual to pour in more than six. These pans cost in Germany eightpence cach. It has been ascertained from Mr. Apsley Pellatt, of the Falcon Glass Works, that glass milk pans, of the size and shape of the specimen, but of white flint glass, (why white?) could not be made for less than 7s. 6d. Another instance this of the baneful result of the duties of restrictions on glass, which have the direct effect of repressing improvements and encouraging fraud. It is a well-known fact, that there is scarcely a manufactory in England, under the control of the Excise, which could be successfully carried on without a greater or less evasion of the laws. Sale of Iron Steam-boats.-On Wednesday, the 3rd ult., the Locomotive, 41 9-10ths tons register, built in 1842, by Messrs. Ditchburn and Mare, with watertight bulkheads, fitted with a pair of engines equal to 25-horses power, length 104 feet 6 inches, beam 11 feet 4 inches, drawing about 26 inches, was sold by auction for 6901. On the same day was sold the iron steam-boat Prince Albert, 290 tons, (o.m.,) built in 1842; she is propelled by two engines of 30 horses power, upon an improved construction, by Messrs. Braithwaite, Milner and Co., with tubular boilers; the saloons of this beautiful vessel were fitted up in June last, with great taste and at considerable expense; length between perpendiculars, 155 feet, beam 19 feet 6 inches, depth 10 feet, sa loons 36 feet each, ladies' cabin 16 feet, engineroom 26 feet 6 inches, draws 4 feet 9 inches with her fuel on board. The biddings, which commenced at 3,000l., were very spirited, and the hammer ultimately fell at 3,7507. INTENDING PATENTEES may be supplied gratis with Instructions, by application (post-paid) to Messrs. Robertson and Co., 166, Fleet-street, by whom is kept the only COMPLETE REGISTRY OF PATENTS EXTANT from 1617 to the present time. LONDON: Printed and Published by James Bounsall, at the Mechanics' Magazine Office, MERRYWEATHER'S CABINET FIRE-ENGINE. (Registered under the Act for the protection of Articles of Utility.) NOTWITHSTANDING the protective forms which fire-engines have been made to assume since their invention, two centuries ago, the appearance of the Cabinet Fire-engine furnishes proof that variety is not yet exhausted. It has long been a custom to provide "the stately homes of England" with engines for preventing the spread of fire, and the advantage of such a provision has on many occasions been strikingly shown. The entrance halls of many mansions are adorned with unique specimens of fire-engines of the best construction and appointment, while in numerous instances the out-houses are made the depositories of fire-engines of a less ornamental character. The forms which these machines have hitherto assumed, have greatly limited, and in the majority of instances precluded their admission, to the more vital parts of buildings, or, when so admitted, have led to their being stowed away out of sight, and consequently out of mind, in the hour of need. The idea of conspicuously placing a properly appointed fire-engine in the drawing-room, the bed-chamber, or the boudoir, has rarely been entertained; and yet, on how many occasions would such an auxiliary, so located, have been invaluable ? The truth is, that the visible mechanism of a fire-engine, with its handles, pipes and buckets, in domestic apartments, is too apt to engender uncomfortable feelings, and to give rise to unfortunate associations; its room has therefore been generally preferred to its company. The present engine, by one of the first makers of the day, was produced at the request of his Grace the Duke of Norfolk, and is certainly the most elegant, as well as the most compact and efficient ever constructed. In addition to more powerful aids located externally, the interior of his Grace's seat, Arundel Castle, is protected by three of these Cabinet Fireengines. The engine is enclosed within a neat mahogany case-stand, mounted on four strong castors, with a handle at each end; and is kept constantly charged with water in readiness for instant application. In the event of a fire breaking out, the top cover of the case is lifted off, which dis plays to view the pump handle folded back, and the branch-pipe affixed to the end of a length of leathern hose which lies coiled upon the shelf of the cistern, as shown in fig. 1. Fig. 3 exhibits the working handle straightened, and the leathern hose extended ready for action. The works of this engine are upon the patent principle, with metallic valves, &c. It is capable of delivering water in a continuous jet upwards of 50 feet high, at the rate of ten gallons and upwards per mipute. The branch-pipe is furnished with Mr. Baddeley's Fire-engine spreader, (a previously registered invention,) which affords the means of covering the whole surface of an apartment, and of extinguishing every particle of fire, with a very small quantity of water: thus limiting the damage done by the two antagonist elements, to the smallest possible amount. In some cases the cover of the engine contains a domestic fire-escape which adds much to its completeness. Whether this engine is considered with reference to the elegance of its appearance, its readiness for application, economy of power, or the perfection of its equipment, it may be regarded as the ne plus ultra of modern fire-extinguishing machinery. When got up in a plainer style, this engine supplies what has long been a desideratum, viz., a machine superior in power to the ordinary garden syringes, and more moderate in cost than the usual fire-engines. There are numberless persons who are sensible that the former are unequal to their requirements, but are unable or unwilling to incur the outlay necessary to obtain the latter; to such persons the Cabinet Fire-engine strongly commends itself, affording, as it does, at a small cost, the maximum effect of a man's power, combined with great compactness of form, and an unusual completeness of equipment. B. THE CAMPHINE LAMPS. Sir,-In your Number 1078 there is a letter from a correspondent, under the signature of "Z. Z.," in which he remarks, that camphine and rectified spirits of turpentine are identical. In stating this he is perfectly correct. Mr. English himself only claims, as you observe in a ON SOUND BY HORATIO PRATER, ESQ. note, his particular process of rectifying the spirit of turpentine: to this process the patent is limited, but whether it is an invention of Mr. E.'s is rather doubtful. Camphine has long been in use in the United States, and is the principal article there used in illuminating shops, public buildings, &c. Soon after the alteration in the import duties, Mr. English, as well as other parties, turned their attention to turpentine, and I have no doubt, that it will now, from its very low price -about 3s. per gallon-become one of the principal commodities used in illumination. I have rectified several samples of turpentine obtained from the manufacturers, and I find that there is but little difference in the quality of them. Various means have been used for the purpose of rectifying and depriving it of its oxygen-of which it contains in general about 8 per cent. It has at different times been brought forward in England as a material well adapted for lighthouses, and in fact, was tried and approved of by the surveyor to the Liverpool Lighthouses (Lieutenant Lord). The then inventor, being short of funds, could not carry the business on, or find any one to assist him. The surveyor having no regular supply furnished to him was obliged to take the camphine lamps out and replace them with the old ones for burning sperm oil. A person of the name of Spratt, residing at Cork, had a patent for, or at least sold rectified turpentine under the name of patent spirit. This he first brought before the public about 1835, and sold in his own neighbourhood a considerable quantity. The price he charged, I believe, was about 5s. to 6s. per gallon. His successor now sells at a reduction of 2s. to 3s. A variety of lamps have been used for burning, but in none have I seen the combustion so complete as in Mr. Young's "Vesta." Though this is only a modification of an American lamp, it is superior from having a nonconducting material interposed between the light and the magazine, and from being also manufactured of better materials, and finished in a workmanlike and elegant manner. The button for deflagration, placed in the narrow part of Mr. Young's lamp, is immovable; in the American it is regulated by a screw. Mr. English, I believe, went to New York previous to taking out his patent. I have been told also that he has had some of 323 the American manufacturers of camphine at his distillery. Several parties now prepare the article, and I believe all prepare it quite as well as Mr. English. It must be borne in mind, that the manufacture of such an inflammable material is attended with great danger. I would also give the consumers a warning on this point, for notwithstanding Mr. Young's ingenious lamp removes much of the danger, still it must be handled with great care, and must on no account be brought near to any flame. There can be no doubt about its being, as Dr. Ure says, (No. 1080, Mech. Mag.) the cheapest of all lights; if anything, the cost is less than the sum which he states. The term Camphine was first given to pure turpentine by the French philosophers. M. Dumas, I believe, originated it. A MECHANIC. Although recent physiological researches have induced me to question whether the received theory of sound be correct, I have nothing to object to the above passage of the learned writer, taken in an isolated sense. I say, taken in an isolated sense, because it is obvious that the author, like natural philosophers in general of the present day, believes that the air is the medium of sound, because it is susceptible of being thrown into undulations; and that it is by such undulations that sound is communicated. Hence, soon after the above passage, we have the following, "The vibration of the particles of air which produce sound," &c. &c., and to the same effect, to the end of the whole of the sections on Sound. Now I have to inquire if sound be occasioned by the undulations of the air, why it is that we can hear the voices of people in a room above or below us when all the doors are closed? while writing this, hear the servants talking in the kitchen below me, though of course I am unable to tell what they say, I can, |