is, however, no need for any personal remarks whatever. If Mr. Hancock is as sincere as I am for the truth, the whole truth, and nothing but the truth, he will prove his sincerity by inserting (with your acquiescence) a verbatim copy of his specification, and drawings attached thereto. Then would the readers of the Mechanics' Magazine be able to estimate the value of Mr. Hancock's pretensions; then would they see that all his patent claims in boilers consist in the inventions of preceding machinists. (I would not hence infer that Mr. Hancock has effected nothing; on the contrary, I believe that some of his contrivances in locomotion are original and good.) If Mr. Hancock shall refuse to subject his pretensions to this fair ordeal, I may admire his prudence, but I shall sincerely regret that he should have so far committed himself, as to make charges that he has no means of substantiating, and to fulminate threats which he would not to execute. It is a most singular feature in Mr. Hancock's letter, that he expresses his indignation at being charged with an attempt to impose upon your readers, and in the very next sentence proves, that such charge was well founded! In his first letter, it will be remembered that he stated himself to have invented, and that he possessed a legal monopoly in, flut-chambered boilers, without any limitation as to the kind; thus suppressing that portion of the truth, which was essential to forming a correct judgment of the real fact. Now, to avoid the claims of previous inventors, which would demolish his broad claim, he is obliged to qualify it down, first, to "constructing narrow flat vessels, in the form and manner hereinbefore described." The form, be it observed, means flat and square (which was adopted by Smith, Dr. Alban, and many others); the manner means, chiefly, the tyeing of the thin flat surfaces together by stay bolts (which was the especial object of Captain Smith's patent, and which I saw, both in the process of manufacture, and in use; and it was, most likely, the interference of Captain Smith's patent that hindered Mr. Hancock from making boilers according to his specification.) Mr. Hancock goes on to say, that these narrow flat vessels are 66 adapted to be placed vertically, or edgeways upwards over the fire, for producing steam for steam engines." Now, is there a reader of the Mechanics Magazine, who will deny that Dr. Alban's square flat plates, of the same proportions too, were not previously placed vertically, or edgeways upwards over the fire for producing steam for steam engines? The third claim put forth is equally Dr. Alban's; but I will not exercise the patience of your readers by the needless repetition of the paralle'.* Although there is much more that might fairly be commented upon, I will here conclude my brief epistle, by observing, with respect to Mr. Hancock's allusion to my description of his boiler in the Engineers' Encyclopædia, that that description was chiefly supplied by himself, and that it had no reference to his patented boiler of 1827, which is an essentially different apparatus. I remain, Sir, your obedient servant, Camden Town, 5th Sept. 1838. COLLIERY COMMUNICATION. Sir,-Eight or nine months ago, having some spare tubing, and being rather inconvenienced by the distance which my workshop is from the front one, I thought of applying tubes to convey the voice from one place to the other, that so I might save unnecessary waste of time and labour. I therefore proposed my plan to some friends, and it met with decided opposition, "it had no chance to answer." However, I resolved to try it, and my labours were completely successful. (Note, when I had my tubes put up I was not aware that the same plan had been in use many years before: indeed I have since seen advertisements, offering to make "speaking tubes" at so much per foot.) My present object is to suggest, through the medium of your useful pages, that such tubes would be very suitable for colliery purposes, obviating the necessity of either signals, or that unearthly yell which is ever and anon pouring *As Mr. Hancock has declared his intention of not proceeding further in this controversy, it is perhaps necessary that we should append a few words to Mr. Hebert's letter. In our last we stated our opinion that if Mr. Hancock can prove himself to be the first inventor and patentee of flat-chamber boilers, his monopoly extends to all mere modifications thereof. As far as evidence has yet been adduced, and in particular, as regards the patents of Smith and Alban, we think decidedly that Mr. Hancock's patent would be legally upheld.-ED. M. M. The Sir,-The above sketches represent a Swiss portable fire-engine, manufactured by Messrs. Bramah and Robinson, Pimlico, for the use of private and public buildings, ships, gardens, &c. working part consists of a horizontal brass cylinder, having a flanch at each end, to which two end-caps or covers are screwed. These caps have stuffingboxes in their centres for supporting, in an air-tight manner, the working axis of the engine. Within the cylinder is placed a strong metal partition or radius, the lower edge being joined to the cylinder, and the uppermost edge, which is grooved, made so as exactly to fit the circle of the latter. The axis is armed with two wings or fans, on each of which is placed a valve opening upwards, to allow the water to pass through them. Fig. 2. These fans are made to move water-tight against the sides and ends of the cylinder, by means of leather on their edges. When the axis carrying the fans is fixed in its place, the groove in the metal partition, described above, is filled with hemp, or some other soft material, so as to press on the under surface of the axis, and cause it to move in a water-tight manner. The fans being a diameter of the cylinder, divide it into two parts, the lower of which is again divided by the radius partition into two compartments; in each of these an aperture is cut through the cylinder opening into the suction-passages; these apertures, like those in the fan, are closed by valves opening upwards. A vibratory motion being given to the fans by means of the lever on their axis, the capacity of the two lower compartments of the cylinder become alternately enlarged and diminished; the consequence of this is, that water becomes drawn up into the cylinder, gets above the fans on either side, and is then forced out through the exit-pipe, the stream being equalized by means of a spherical air-vessel placed above the working cylinder. This engine is mounted in a wooden tub, as shown by fig. 1. The working cylinder is concealed by the side of the tub, but the air-vessel A is seen. BB are the lever handles by which the engine is worked; for the convenience of carrying about, they fold up, as `shown at fig. 2. If made so as to work by suction from a pond, reservoir, cistern, &c., as well as from its own tub, the suction-pipe is attached to a screwed orifice C, its course being denoted by the two dotted lines D. A short metal branch-pipe is affixed to the ascending tube of the air-vessel by means of a flexible leather hose E. FF are two handles by which the engine is lifted. As the weight of this apparatus is under 100lbs., it can be readily carried by a man; for this purpose two shoulder straps are permanently attached to the engine. The mode of carrying is shown by fig. 2. This is a very compact engine, of considerable it may power; be worked by one man, but when two are employed, about twenty imperial gallons of water are discharged per minute to a distance of nearly 70 feet horizontal, or 50 feet high. To be really useful as a fire-engine, however, it is absolutely necessary that the machine should be furnished with a good length of leather hose, for it is next to impossible for any person to stand within an apartment where a fire is raging, and work the engine to any good effect; the labour and excitement, (leaving fear out of the question) would cause an increased respiration, which the heated and contaminated atmosphere of the apartment would very ill supply. One of the best authorities on this subject, Mr. Braidwood, in his treatise on fires and fire-engines, remarks:-"Much has been said about the convenience of conveying small engines up stairs, and into places where the fire is raging; but I fear that those who have so strongly recommended them have never made the experiment. I have generally found that all the fresh air to be had in a burning apartment is required, to enable a man to lie on the floor, and direct the water from the hose, while the engine is being worked by those on the outside." Portable engines have advantages enough to recommend their general adoption, without attributing to them powers which they can never possess; they are calculated to be eminently serviceable at the infancy of a fire, but it is not by placing them in an unpleasant and even dangerous situation, that their advantages can ever be fully realised. It is a misunderstanding of this kind that has operated to limit the adoption and practical application of many ingenious machines that have from time to time been constructed for the speedy extinction of fires; I trust, however, that the time has now arrived, when a more general diffusion of the proper mode of proceeding in case of fire will tend to nip these accidents in the bud, and render available the several mechanical aids which have been designed for this important purpose. I remain, Sir, yours respectfully London, August 30, 1838. TRANSPOSING PIANO-FORTE. Sir, I have had an idea of extending the range of amateurs' singing, by means of a transposing piano-forte, for many years. Various have been the attempts at simplifying transposition: an instrument was once attempted to be introduced, in which all the keys were alike with respect to fingering, but were placed black and white alternately. This, however, presented so many difficulties to those who had acquired a knowledge of the usual mode of fingering, that it did not succeed. My plan is as follows:-Let the instrument be strung with five additional wires above and also below the compass of the keys; let the key-board move on rollers, by means of an adjusting screw, and an indicator made to show whether the key-board is screwed 1, 2, 3, 4, or 5 semitones above or below the pitch (suppose concert pitch) of the instru ment. I need not point out to an instrumentmaker the alterations in bridges, hammers, &c. contingent on this plan. I am, Sir, yours, AN OLD CORRESPONDENT. Hitc in Herts PRACTICAL SQUARING OF THE CIRCLE. Sir,-Understanding that contributions connected with mechanics are acceptable for the columns of your Magazine, I send you the accompanying demonstration of the square of the circle, as applicable to the measurement of trees and other cylindrical bodies. The mathematician will not object to a subject of scientific study since the days of Euclid and Archimedes, as it affords, I believe, the readiest and nearest practical data, as a relative proportion between the square and circle, ever yet offered to the public in integers, and the young arithmetician, or humble artisian, will be able by it to make his calculations free of decimals and fractional parts. To the private gentleman wishing to ascertain the dimensions of the beam that he can get from a tree; to the merchant in purchasing timber; to the builder, the mechanic, and in short, for numerous purposes, it may be found useful in simplifying and shortening calculations. The author, Captain Cortlandt Taylor, of the Madras artillery, when on a mission in 1837, from the Madras government to the Malabar coast, to procure teak timber for the government guncarriage manufactory, forwarded it with some calculations in the reduction of logs, to the military board of that presidency. I am, Sir, your obedient servant, London, July 23, 1838. The square of the circle, and its adaptation to measuring of timber and other cylindrical bodies. D meters (A C, and BD perpendicular to each other; then are the triangles AEB, BEC, CED, and DEA (formed by the radii of the circle and the points A, B, C, and D being joined), right angle triangles and similar; having the common centre E a right angle in each; the legs A E, BE, C È, and D E (or circles radii,) equal; and the lines or hypothenuses A B, BC, CD, and A D, also equal, and together forming an inscribed square to the circle ABCD. Then, as the circumferences of all circles are to their diameters, as 3.1416 is to unit. So 3.1416 is to 1, as the circumference of any given circle ABCD, is to its diameter, DB: but D B the diameter is the double of EB,-the radius; and EB is one leg or side of the right angle triangle A E B, of which AE is the other leg, and A B, is the third side, or hypothenuse. Then, as in right angle triangles, the square of the hypothenuse is equal to the sum of the squares of the other two sides, in the right angle triangle AEB, BE2+A E2=A B2: but as BE, and A E are equal, their squares are equal also, therefore 2 EB2=AB2, or √2 EB2=AB, the one-fourth of the perimeter of the required square. Thus, knowing the circumference of any circle, the perimeter, or measurement of the inscribed square can be easily ascertained; and vice versa, knowing the square the circle can be obtained, and the difference, (or loss on the latter being squared,) is known. Practical Illustration.-To illustrate this demonstration by numbers: In the above figure, assume the measurement of the inscribed square* A B C D at 100, (one hundred, say inches,) of which the side A B is one-fourth or (twenty-five,) 25. Then in the right angle triangle A B E, (as before), the square of the hypothenuse (or side A B), or 252, is equal to A E2+E B2, that is 625 = A E2+ EB; but as AE and EB are radii of of the same circle and equal, their squares are equal also, and 6252 E B2, or 625 A E2, or √25 = E B, or again √312.5 =EB. (Extract root of 312.5-) 312,5)17,6776 the root. 2 = Let A B C D be a circle, and the dia *This is working the reverse way, but as it enabled me to come, by a single process, to the required information, it was adopted. Sir,-In your Magazine, No. 775, p. 168, I notice a letter from a Mr. J. Murray," in which he deprecates the use of "Perkins's pipes." I have seen the heating apparatus by those pipes successfully used for many years, without having produced any of the evils he ascribes to them, evidently because his "knowledge" does not "extend" to their efficient practical application. The term red-hot, as applied to iron, conveys an idea of ignition, but I have yet to learn that this term applied to water, excites any such association or its consequent alarm. Red-hot water could not have set the building at the Manchester Botanic Garden on fire-of this his knowledge of its elements should have prevented him giving credence or publicity to any such an allegation. I am desirious he should have the practical benefit of the maxim "audi alterum partem." That his mind may be disabused of the mere abstract impression of this subject which it has received, and if he will call upon me, I shall be able to show how an heating apparatus formed exclusively of these pipes, which have for years been used with uninterrupted safety, and that the owner APPARATUS. does not wish "to get rid of them," but deems them a valuable improvement. Any defective pipe is always discovered on being first properly tested by the workmen that construct the apparatus, by noticing any fissure therein, or emission of steam, so that no danger need afterwards be apprehended if superintended with common care. Yours most respectfully, JOHN DORNING. Wavertree, near Liverpool, Sept. 8. 1838. PS.-Will thank you to inform me if the writer of the letter alluded to be Mr. J. Murray, the chemist and lecturer, of Hull, or some other gentleman of the same name, as probably I shall write to him on this subject.-J. D.† 72 1000 *The decimal .072, or per cent. may, for any practical purposes be omitted as insignificant, but should a greater degree of accuracy be required, it may be obtained, I may say to fractional nicety, by the addition of unit to the sum of percentage of every 1400,-which would so be 14 x 11-154+1= = 155; or as 1400 is to 1555. The proof of the correctness of this demonstration is, that decimal .7071 is the side of an inscribed square, the diameter of the circle of which is unit:-Then, as 1555 is to 1400, so is 3.1416 to its inscribed square 2.8384, the side or one-fourth of which, is .7071.-Q ED. + Mr. Murray, of Hull, we believe -ED. M. M, |