new iron steamer, the machinery for which is made by Messrs. Seaward and Co., the highly respectable engineers at Limehouse, upon what may be termed the new-old plan, or, in other words, the atmospheric principle revived, I beg to observe, that, notwithstanding the admirable and satisfactory manner the engines are therein stated to have performed, that there are some inaccuracies in the statement-first, as to the distance from Blackwall to Gravesend-secondly, in having made that passage in less time than any other steamer. The distance from Blackwall to Gravesend instead of being 22 miles, as set forth by your correspondent, is, I believe, generally known to be under 20 miles, and this inaccuracy would, if admitted, give to the Atmospheric* a fictitious speed in her favour of two miles in the hour, and really have a tendency to make her appear the fastest boat, and also to mislead the public mind. Of her having beaten the Railway steamer, I cannot either admit or contradict; if, however, it be so (notwithstanding the advantage, she would have, being at present little more than a shell in weight, without cabin fittings, stores, &c., while the Railway, in addition to the usual freight, was interrupted in her passage by stoppages to take in, and put out passengers on the way, which is not the case with a boat running an experimental trip) the Atmospheric has done well. Still the supposition that the Atmospheric, in having made the passage from Gravesend to Blackwall in 1 hour 74 minutes, is the shortest time in which the passage has ever been made is far wide of the fact, it being well known that each of the Blackwall Railway Company's boats, excepting the Brunswick, have several times performed the distance in one hour and from two to four minutes; and upon one occasion, it will be found upon reference to your Magazine of July 10, 1841, No. 935, as stated by " Justice" in answer to "Nautilus," on June 18, No. 933, that the Blackwall made the passage on June 11, in 58 minutes, which, I believe, is the quickest passage on record. Should the Atmospheric take a station on the Thames, fully equipped for service, and perform the passage in less time than the one by the Blackwall on the 11th of June, 1841, she will be justly entitled to be placed A 1; and yet it is hardly a question whether the novelty of the adoption of atmospheric agency will answer any very great end, or warrant by the bold attempt the hazard of public approval; perilled by the employment of a principle deemed by the great master mind incomplete, and for the remedy immortalized the name of Watt. • Called se for distinction, not having, as yet, any name. By giving this a place in your highly valued journal, you will greatly oblige a constant subscriber, and a lover of fair play, anxious that every one should have the just praise due to his merit. I am, Sir, Your obliged and obedient servant, VERITAS. [We are obliged to our correspondent for setting us right as to the passage of the Atmospheric from Gravesend to Blackwall being the swiftest on record. What the distance really is-whether 20 or 22-matters nothing, so far as the comparison with other steamers goes. In the trial with the Railway, care was taken that the Atmospheric should stop every time the Ra lway stopped, and not resume her way till after her competitor had resumed hers. No doubt the fact of the Atmospheric being so lightly loaded was in her favour; but some allowance must also be made, on the other hand, for the newness of her engines, and (we may here add) for their not being very well secured to their bearings-a circumstance which caused palpably a great increase in the resistance which the steam had to overcome. As to the authority of Watt being unfavourable to this application of the atmospheric principle, we should think it of great weight if we did not remember, also, that he thought, for a long time, the navigation of the seas, by steam power in any shape, to be impossible. In the description which we gave of the pistons, and the importance we ascribed to their peculiar form of construction, we took the enrolled specification of the invention, which was patented about two years ago, for our guide; but another correspondent (R. O.) informs us that the middle groove is not filled with steam, but with melted tallow; and this we find on inquiry to be the case. The same writer points out an obvious typographical error in the dimensions assigned to the floats, which are of course of the same area on both sides, namely, 9ft. 6in. x 14in.-ED. M. M.] The operation of cutting this frigate in two, in order to her enlargement, and conversion into a steam-vessel of higher power than any yet afloat, (the intention to do which we were the first to announce two or three months ago-see Mech. Mag. for April 9,) was performed at Chatham Dockyard on the 18th ultimo. The following particulars of what took place on the occasion, we extract from the Hampshire Telegraph. "Two large booths were erected on each side of the Penelope, and were filled by naval and military officers and the gentry of the neighbourhood. The sight was novel and astonishing. Three ropes were fastened to the gunwhale of the ship from three capstans, which were fixed in the ground facing the dock, and which were worked up by windlasses by nearly 200 convicts. On the arrival of the Rt. Hon. T. Cory, one of the Lords of the Admiralty, together with Sir W. Symonds, the surveyor, and Captain R. Brandreth, architect of the navy, Captain Superintendant Shirriff, and other officers, the master builder, Mr. Fincham, gave directions for all hands to work. As soon as the parts were observed to separate, the band of the dock-yard struck up, Oh dear, what can the matter be?' amidst the cheers of the assembled multitude. The fore part of the vessel was ob served easily to glide up the dock. The fore part of the ship having been brought up to the mark allotted, left a space between the two parts of the ship, exactly 62 feet, which will lengthen her to about 190 feet." THE SOLAR ECLIPSE OF JULY 8.Professor Silliman's Journal of Science and Arts, for January, 1842, contains an article "on the Solar Eclipse of July, 1842," in which it is observed-" As the approaching eclipse will excite great interest throughout Europe, and especially in those places where it will be total, it is earnestly hoped that particular attention will be paid by those favourably situated and in the possession of suitable instruments, to the determination of the correctness of a recent suggestion-that the irregularities so frequently noticed at the second and third contacts of nearly central eclipses, and at all the contacts of the transits of Venus, may be seen or not at the pleasure of the observer, according as the colour of the dark glass he applies to his telescope is red or green." The committee of the Philosophical Society of Philadelphia, in their report on this eclipse, remark, in reference to this suggestion of Professor Silliman, "The suggestion is one of the greatest importance, as it seems to furnish evidence of the existence of a lunar atmosphere, through which, as through our own, the red rays have the greatest penetrative power. It also leads to new views concerning the cause of the remarkable appearances of the beads of light and the dark lines frequently noticed, since it shows that their appearance may be completely modified by a change in the colour, and consequently in the absorbing power of the screen glass through which they are observed." "It is believed," Professor Silliman further remarks, "that on another account will this suggestion, if well founded, be of great importance, viz., in its obvious tendency to diminish, if not wholly remove, the discordances not unfrequently found in the best observations on solar eclipses, and transits of Venus, and which, with regard to the latter in 1761 and 1769, were so great as materially to diminish the value of this me. thod of determining the distance between the earth and the sun. American Horse-rake.-In some parts of the country, where labour is very dear, they use a machine for raking the hay, called "the Flexible Horse rake." It is distinguished from all others by a joint in the centre of the head, by which the rake contracts to any uneven ground, and takes the hay clean. Also, by the form of the teeth, which glide over hillocks or stones, like the runner of a sled. This rake has also a smooth back-board, on a level with the teeth which support it; and it is not liable to become entangled with the hay, when canted over to be emptied. Twenty-four acres a day are raked perfectly clean with this instrumentone man holding it, a small boy riding the horse, The labour of managing it is less than that of holding a small plough.-Le Cras. LIST OF PATENTS GRANTED FOR SCOTLAND FROM 25TH OF MAY TO THE 23RD OF JUNE, 1842. Joseph Clisild Daniel, of Tiverton Mills, near Bath, for improvements in making and preparing food for cattle. May 25. Robert Logan, of Blackheath, Kent, Esq., for improvements in obtaining and preparing the fibres and other products of the cocoa nut and its husk. May 28. Thomas Henry Russell, of Wednesbury, Stafford, iron-tube manufacturer, and Cornelius Whitehouse, of the same place, for improvements in the manufacture of welded iron tubing. May 28. Thomas Middleton, of Loman-street, in the borough of Southwark, Surrey, engineer, for an improved method of preparing vegetable gelatine, or size for paper, and also an improved mode of applying the same in the manufacture of paper. (Being a communication from abroad.) June 6. John Railton, of Blackburn, Lancaster, machinemaker, for certain improvements in machinery, or apparatus for weaving. June 6. Thomas Hedley, of the town and borough of Newcastle-upon-Tyne, gentleman, and Cuthbert Rodham, of Gateshead, Durham, millwright, for an improved apparatus for purifying the smoke gases and other noxious vapours arising from certain fires, stoves, and furnaces. June 7. John Burnell, the younger, of High-street, Whitechapel, Middlesex, manufacturer, for improvements in the manufacture of leaves or sheets of horn, commonly called lantern leaves, and in the construction of horn lanterns. June 8. Otto Rotton, of Gracechurch-street, London, doctor of medicine, for certain improvements in machinery, or apparatus for spinning cotton, wool, and other fibrous substances. (Being a communication from abroad.) June 14. John Bould, of Ovenden, Halifax, York, cottonspinner, for an improvement or improvements in condensing steam-engines. June 23. John Cox, of Gorgie Mills, Edinburgh, tanner and glue manufacturer, for certain improved process of tanning. June 23. LONDON: Edited, Printed, and Published by J. C. Robertson, at the Mechanics' Magazine Office, MERRYWEATHER'S RAILWAY FIRE-ENGINE. Sir,-The accompanying drawing represents a powerful fire-engine recently built for the London and Birmingham Railway Company, by Mr. Merryweather, of Long Acre, London. This engine is the largest ever constructed for land service in this or any other country, the celebrated steam fireengine not excepted. The pumps are two gun-metal cylinders, 9 inches in diameter, with a 10 inch stroke, and work into a spherical copper air-vessel, the capacity of which is nearly twenty gallons. The cistern, which is 13 feet long, holds, when full, four hundred and fifty gallons of water. The pistons and valves are of metal, the latter being placed in separate and easily accessible valve chambers; these excellent valves were fully described at page 325 of your xxviith volume. The water passages are 3 inches and a quarter in diameter. The handles when opened out are 23 feet long, but they fold up fore and aft, so as not to project beyond the length of the cistern; when extended they are kept straight by a sliding bolt of a simple and ingenious description. Each end of the engine is fitted with spring buffers, attached to a buffer bar or frame, which is kept up by a pin-bolt, and hinged below so as to fall down out of the way of the handles and levers when the engine is set to work. In the fore part of the engine is placed a hose-reel* capable of carrying upwards of ten lengths (i. e. 400 feet) of riveted leather hose, all joined up, the whole, or any portion of which can be run out and attached to the engine in a few seconds. In the pockets on either side are stowed away two lengths of suction-pipes, one long and one short branch-pipe, of the construction described at page 37 of vol. xxv.; with a complete set of nose-pipes, from an inch and a quarter down to three quarters of an inch in diameter. A leather portable dam, of suitable dimensions, with a proper complement of axes, crowbars, wrenches, &c., complete the equipment of this stupendous engine. Described in vol. xxvii. page 34. A trial of this engine took place recently at the Euston-square Station before a number of railway directors, government officers and scientific gentlemen; the handles were manned by 42 of the railway servants, when a single jet, an inch and a quarter in diameter, was thrown in a compact form upwards of one hundred feet high; an inch and eighth jet was thrown considerably higher, and afterwards two jets of three-quarters of an inch in diameter were delivered at similar elevations. The trial took place under considerable disadvantage, from the deficiency of the present water supply, the small main from the Camden-town reservoirs being wholly inadequate to afford water with sufficient rapidity to meet the demands of an engine of this calibre. The name of "Niagara" has been given to several tolerably powerful engines, but if ever it was appropriately bestowed, it would be on the Railway Fire-engine. The London and Birmingham Railway Company have been tolerably exempt from accidental fires, and when they have occurred, from the judicious precautions taken, have been promptly extinguished. The capabilities of the present engine, as regards working and travelling, are such, as to afford most sufficient protection to the extensive establishments of the Company at Camdentown, Wolverton, and other stations, as well as to all property adjacent to the line of railway. The performances of the engine, as well as the excellence of the workmanship, and the skill displayed in adapting it to the peculiar service for which it is intended, gave great and general satisfaction to all who saw it, and fully sustain the deserved reputation of Mr. Merryweather in this branch of manufacture. I am, Sir, Yours respectfully, WM. BADDeley. 29, Alfred street, Islington, June 21, 1842. MR. C. W. WILLIAMS'S FURNACE AS APPLIED TO MARINE BOILERS. Sir,-In sending you the following Report of experiments made by Mr. Parkes on a marine boiler, showing the difference between the old and new mode of effecting combustion in furnaces by the admission of air behind the bridge, I accompany the tabular view of Mr. Parkes's results by those of two other experiments with the same boiler and furnace the one testing the new mode, under the circumstances of a slower rate of combustion, by heavy charges, and the other, with a reduced area of furnace. These results are highly instructive, and sufficiently prove the necessity of going further into the enquiry. In my next I hope to be able to give you some additional tables of the same character on this interesting subject, as laid before the British Association in Manchester. as regards the fuel, (namely 9.30lbs of water evaporated by each pound of coal,) was, in truth, the least economical, when time was taken into account. In this case, but 1030 lbs. of water were evaporated per hour, whereas, when the economy of fuel gave but 7.8lbs. of water per lb. of fuel, there were no less than 1715 lbs. of water evaporated within the hour. No. 1 and 2. Experiments by Mr. Parkes the former, on the old system of excluding air from the gases behind the bridge the latter, on Mr. Williams's plan of admitting the air. No. 3. Experiment by a slower rate of combustion, with heavy firing-air admitted on Mr. Williams's plan. No. 4. Air admitted and active combustion, the area of the fire-grate having been reduced. These experiments show the difference between the old and new systems. They also show how little dependence can be placed on any test, drawn from the mere weight of water evaporated by each pound of coal. In the above, we see that the experiment which gave what would be considered the most economical results Thus we see that what would here have been called economy, might be the ruin of the manufacturer; for although each pound of coal would, per se, appear to do the largest work of evaporation, still, as less was done within the hour, it is manifest that, on the whole, less work would be done by the engine; and, as the weight of water evaporated within any given time may be taken as the representative of a given quantity of work done by the engine and the machinery it put in action, so the true measure of economy will depend, not on the quantity of water evaporated by each pound of coal, but on the time required for such evaporation. The column showing the temperature of the escaping products (which are here for the first time, that I am aware of, brought into the account) is of the highest importance, since we find that, exactly in proportion as the quantity of water evaporated per hour was increased, so was the temperature of the products escaping by the chimney. This, although it is really so much extra work done by the fuel, has hitherto been overlooked; yet here lies, perhaps, the greatest source of practical available economy yet within our reach. Until we learn, therefore, how to turn this extra labour of the fuel to the work of evaporation, we are not in a position to determine, either the value of the fuel, or the description of furnace in which it may be best consumed. In my next I hope to be able to lay before your readers the practical results of a mode of estimating the temperature of the flues of boilers, as laid before the Association by Henry Houldsworth, Esq., of Manchester. By this ingenious_but simple plan, Mr. Houldsworth has effected what has so long been a desideratum, namely, the means of ascertaining not only the relative heating powers of different kinds of coal, but of the different |