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STEAM BOILER EXPLOSIONS.

ments, and cannot yet say which is most to be admired, his immense satisfaction with his immense discoveries, or his profound contempt for all other writers of all other countries. Witness his remarks on Hamelin's patent mastic cement, page 35, Article xxxiii. of his Appendix. “This very ingenious composition, which forms an excellent stucco, shall be noticed here, though invented by a Frenchman." What amazing condescension in the learned Colonel!

From Colonel Pasley's work it would seem as if he were acquainted with the life, birth, and parentage, of every person who has ever cemented, yet in this one instance, at least, had his scientific reading been only equal to his national prejudices, he might have spared himself the trouble of this passing compliment to "the Frenchman," for true it is that the same cement had been invented in England a century before Hamelin's time had been actually patented under the same quaint name of Mastic, and had been the subject of suits of law for infringement of the patent, &c., &c.

I should like, by the way, to be informed whether there is any of this old mastic plaster now to be found in England of the age of a century, because, if there is not, the fact will prove it to be a substance of no great durability, and furnish a caution against its renewed use.

The contempt of Frenchmen, shown in the above extract, however natural in the noble Colonel, seems rather inconsistent at this time of day, when England and France have become wise enough to be friends, and the more so, considering that the Colonel, in his compilation (which he has mistaken for knowledge) has occupied no less than twentyeight pages of his work in copying M. Vicat's treatise on limes, published twelve years since; and forty-one pages of his work in copying M. Tredescant on the same subject.

As writing a large book is considered by many a proof of great erudition, and as the writing of a book on a learned subject may by many be mistaken for great proficiency in the science of which it treats, and as the matters embraced in the Colonel's work are of very great importance, -as he has made himself much more free than welcome with my name, and with my works, which he has in many cases grossly misrepresented, from not understanding them, I send you this

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letter as the first of two or three, in which I intend to show the numerous mistakes the Colonel has made, and to do my best to place the whole subject in a better light.

That more information is neededthat more information will be usefulthat if nothing more than a classified statement of the knowledge already generally possessed were published, many ignorant and absurd attempts at improvement would be prevented, and many and large improvements in building become of easy and certain attainment-all must readily allow. An amazing proof of this has been furnished in England, in the late prodigious attempt to improve calcareous cements by cookery instead of chemistry.

I shall address you in continuation at an early day. Give me but a fair hearing before my country; I have sins enough without misrepresentations, to answer for; and it will be seen hereafter, that to misrepresent what I have done, is to do what neither you, nor your numerous readers, will, I am sure, ever willingly do,-misrepresent the cause of science.

I am, respectfully, dear Sir, yours,
JAMES FROST.

STEAM BOILER EXPLOSIONS-SUGGESTION FOR THEIR PREVENTION.

Sir, I believe it is generally understood that the explosions of steam boilers are occasioned by hydrogen or some other gases accumulating and mixing with the steam in the boilers; at least, that some kind of explosive mixture takes place, by which the boilers are burst, the boiler valves not acting at times properly, or not opening sufficiently to allow of the escape of the mixed vapours or gases into the open air. If so, would it not be a good plan to blow a steady stream of air heated to the most suitable degree, into the boiler, and downwards upon the surface of the water? A valve should of course be affixed to the boiler to discharge the air again from the boiler; that valve being fixed upon a principle of continued action. Perhaps the valve should be kept in action by the engine itself. The hot air would not only purify the boiler of all foul gases, but would accelerate the generation of the steam. I am, yours, obediently, THOMAS DEAKIN.

Blaenavon, April 7, 1842.

NAYLOR'S APPARATUS FOR INCREASING THE ILLUMINATING POWER OF COAL GAS. Fig. 1.

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Sir, I send you a drawing and description of a new piece of apparatus for increasing the illuminating power of coalgas, which I hope you will insert. Chemists have all allowed that carburetted hydrogen owes nearly all its illuminative power to the accidental admixture of a certain oily vapour which is given off during the decomposition of the coal in the retorts; being aware of this, it occurred to me that if the gas could be more strongly impregnated with a similar compound, the flame would be increased in intensity, which I afterwards found to be the case. The apparatus consists of a brass reser

voir or chamber A, attached to the end of the gas-pipe near the burner. This reservoir may be in the shape of an oilflask, made air-tight, with a screw-joint B, or other means for supplying it with any highly volatile oil, as turpentine, mineral naphtha, or the hydro-carburets, and should be kept about half-full. Into this reservoir the common gas-pipe C, ascends a little above the oil D; a very small jet-pipe is branched off below this chamber at E for the purpose of applying thereto a minute gas flame, so as to cause a sufficient evaporation from the oil to unite with the gas previous to its being

NATURAL PHILOSOPHY FOR BEGINNERS.

consumed. The whole is of course surmounted with the usual burner and lamp glass.

By employing this apparatus for burning coal-gas, the intensity of the flame will be very considerably augmented; consequently the same degree of light may be obtained with a far less consumption of gas, a point which I consider of some importance. It may be also employed for burning those varieties of gas obtained by the decomposition of several of the species of anthracite, bituminous earths, wood, &c. which could not be otherwise employed with any advantage for the purpose of illumination.

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should ever voltaic electricity be extensively used as a motive power, the large quantities of pure hydrogen, evolved from the copper or platinum plates of the battery, might be collected and effectively consumed by the new apparatus.

In conclusion, I may remark that the apparatus, from the simplicity of its construction, might be manufactured at a very trifling cost, possessing likewise the advantages of being very compact and neat in appearance.

I am, Sir, your obedient servant,
T. W. NAYLOR.

April 3, 1842.

NATURAL PHILOSOPHY FOR BEGINNERS."

We cordially recommend to all beginners in the study of Natural Philosophy -whether young or old-a little work which has been recently published under the above title. It was originally intended as an explanatory accompaniment to an excellent set of educational models (of the Mechanical Powers, Geometrical Solids, Architectural Solids, &c.) manufactured and sold by Messrs. Taylor and Walton, the publishers of the work; but during its progress through the press, it gradually assumed its present enlarged form of a complete treatise on the mechanical powers, illustrated by reference to diagrams as well as models. The author has executed his task with ability. His descriptions are exceedingly simple, clear, and intelligible; and his demonstrations of principles such as any person

Natural Philosophy for Beginners. Being Familiar Illustrations of the Laws of Motion and Mechanics. Intended as a Text Book for Schools and Self-Instruction, as a Companion to the Lecture Room, or for Model Schools. Illustrated by 143 engravings on wood. 127 pp. 32mo. London, Taylor and Walton.

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with a knowledge of common arithmetic, may readily comprehend. As a Text Book for Schools, or a vade-mecum, to persons who must instruct themselves, we know of nothing better in our language. We select a couple of specimens:

The Wedge.

"There is scarcely any instrument whose applications are more numerous than those of the wedge; chisels, nails, awls, needles, axes, sabres, &c., all act on the principle of the wedge. It is also used in a variety of cases where the other mechanical powers would be of no avail. This arises from its being driven principally by impact; the momentum of the blow is consequently much greater in comparison to the application of the pressure of the lever. As an example of the enormous power of the wedge, it may be stated that the largest ships when in dock may be easily lifted up by driving wedges under their keels. It has sometimes happened that buildings-such as a heavy chimney for a furnace—have been found to incline, owing to the dampness of the foundation, and have been restored to their perpendicular position by wedges driven under one side. It is sometimes used in splitting rocks, which it would be impossible to effect by the lever, wheel and axle, or pulley; for the force of the blow or stroke shakes the cohering parts, and makes them separate more easily. In some parts of Derbyshire, where mill-stones are obtained from the siliceous sand-rocks, wedges made of dry wood are driven into holes bored round the piece of rock intended to be separated from the mass; these wedges gradually swell by the moisture of the earth, and in a day or two lift up the mill-stone without breaking it. Builders, in raising their scaffolds, always tighten the ropes round the scaffolding-poles by means of wedges driven between the cords and the poles.

"A knife may be considered as a wedge, when employed in splitting; but if the edge be examined with a microscope, it is seen to be a fine saw, as is evident from the much greater effect all knives produce by being drawn along the materials against which they are applied, than what would have followed from a direct action of the edge.

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"It appears from the results of some

experiments made in the dockyard at Portsmouth, on the comparative effect of driving and pressing in large iron and copper bolts, that a man of medium strength, striking with a mall weighing 18 pounds, and having a handle 44 inches in length, could start or drive a bolt about one-eighth of an inch at each blow, and that it required the direct pressure of 107 tons to press the same bolt through that space; but it was found that a small additional weight would press the bolt completely home."

The Screw.

"The uses of the screw are innumerable. It is used in coining, where the impression of a die is to be made upon a piece of metal. It is also employed in taking off copper-plate prints, and for printing in general. By its aid a large bale of cotton is condensed into a small package, and from being the lightest and most buoyant of substances, becomes dense enough to sink in water. Sometimes buildings are raised from an inclined to a vertical position, by means of a small screw, acted upon by a comparatively small force. It is also of great utility in astronomical calculations, by affording an easy and very exact method of measuring or subdividing small spaces. An ordinary screw will divide an inch into five thousand parts; but the fine hardened steel screws which are applied to the limbs of astronomical instruments, will go much further. In this case it is called a Micrometer screw, from the Greek μικρός, little, and μέτρον, a measure. The gimlet and auger are examples of the screw, both of which may be considered as an inclined plane wrapped round a cone instead of a cylinder. The power of these instruments is very much increased by their terminating in a point. When liquids or juices are to be expelled from fruit or vegetables, the screw is generally used. The cider press is an example of this machine, so applied; and in cases where great pressure is required, the power of the screw is often employed.

"It is not unfrequently used in flour mills for pushing the flour which comes from the mill-stones to the end of a long trough, from which it is conveyed to other parts of the machinery, in order to undergo the remaining process. In this case the spiral threads are very large, in proportion to the cylinder on which they

are fixed. A common corkscrew is the thread of the screw without the spindle, and is used not to correct opposing forces, but merely to enter and fix itself in the cork. Complicated corkscrews are now made, which draw the cork by the action of a second screw, or of a toothed rod or rack and pinion."

VELOCIPEDES-A FEW PRACTICAL HINTS.

Sir, I have read with much pleasure Mr. W. Pearson's description of his design for a "velocipede," (No. 968,) and as I have been cogitating for some time on the same subject, namely, the applying motive power for carriages (whether that power be manual labour, steam, or other agent) to propellers, to be brought in contact with the ground instead of the cranked axle of the bearing wheels, I may perhaps be allowed to offer some remarks on your ingenious correspondent's suggestion.

I think Mr. Pearson is in error in proposing wheels of so large diameter as 8 feet. Such wheels would be monstrously unwieldy, and the leverage to be overcome would more than counterbalance any supposed advantage to be derived from them. Instance Mr. Brunel's experimental ones on the Great Western Railway, which he was obliged to abandon from the cause stated. I should say that 5 or 6 feet is the utmost practicable limit for wheels of such a carriage; still retaining, however, the full diameter of 3 feet for the guide-wheel. I think that in general, guide-wheels are disproportionably small. The power expended in lifting the guide-wheel, and all the apparatus at the fore frame of the carriage by every action of the propellers, would detract considerably from the advantages otherwise derivable from them. The simple remedy for this would be to have the propellers 2 or 4 in number affixed to an axle, with the same number of cranks underneath the body of the carriage, leaving the guide-wheel at liberty to apply itself to the use which its name indicates. These propellers should be directed backward at such an angle as practice may determine to be best; and there should be an adjustive apparatus for inclining them to any degree found most convenient, or rather efficient, to counteract shocks. In order also that they may adapt themselves to the inequalities of surface, each propeller should be provided with a spring of strength sufficient to bear a moderate degree of pressure, and which, on meeting with any obstacle, would bear a compression of 3 or 4 inches. This spring might be placed in any part of the

SPECIFICATIONS OF RECENT ENGLISH PATENTS.

propeller-perhaps the best position would be at the top, uniting the propeller to the crank. A strong spiral spring I think the best.

The most efficient method of applying power is the next thing to be considered. No doubt the hands are best adapted to this purpose-applied to the levers in the way boatmen use their oars in pulling. Sitting in a natural position, with the feet firmly fixed against a board, the strength and muscles of the whole man, legs, loins, shoulders, and arms, are brought into play; and by thus distributing the exertion equally, many hands make light work." The levers should both be worked precisely together, as the boatman pulls his two oars at once, and should describe as small an arc as possible. I think this would be conveniently done by connecting them by rods to a pair of horizontal knee-joint levers, in connexion with two of the propeller cranks. I cannot at present give a design of such a carriage to illustrate my suggestions, but if your correspondent, Mr. Pearson, or any of your readers wish it, I will furnish one with details. I am, Sir, yours, &c.,

GEORGE ROBINSON.

London, 26th February, 1842.

[The plan referred to by our correspond. ent, in a postscript to his letter, we shall be glad to receive.-Ed. M. M.]

WALKER'S HYDRAULIC ENGINE.

Sir, I have seen in the Mechanics' Magazine two accounts of a hydraulic machine patented by a Mr. Walker-the first account by Mr. Baddeley, the second by a Builder. The subscriber was at Madras in 1822, when a person, by the name of Wood, made a machine exactly corresponding with Mr. Baddeley's description and drawing. It was for the purpose of drawing water in greater quantity than in the usual way, as the ship was very leaky and heavy laden. The passengers made a subscription for the inventor. Wood was carpenter on board, and the commander, his brother. It was spoken of in high terms at Blackwall at the time, as the ship was considered to have been saved by the invention.

Your obedient servant,

SAMUEL TOZER. 12, High-street, Kensington Gravel Pits, April 7, 1812.

WALKER'S HYDRAULIC ENGINE. Sir,-In perusing your 971st Number, Mr. Baddeley's communication adverting to "Walker's Hydraulic Engine" came under

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my notice and I now beg permission to lay before your readers a few remarks upon it.

As to there being any advantage obtainable from the peculiar construction and operation of this engine, I consider it a perfect fallacy. The plain facts are these: firstly, that in its first action it is neither more nor less than a lifting pump; and in its second a forcing pump; secondly, that these two operations are required to obtain the result of one action, of either the common forcing or lifting pump-and, finally, that it is only under particular circumstances, and in par ticular places that it can be applied. The valve being at the botton of the elevator, according to Mr. Baddeley's statement, (by the bye, not the right place after all,) the upward motion of the elevator must conse quently have to lift the whole weight of water in that tube above the valve, and I defy Mr. B. to show that this weight of water is in any way counterbalanced (as he says) by the other elevator, while in action: now this is the lifting operation-differing in its results from the common lifting pump in this important particular only, that the lift does not discharge its water, but requires to be forced out by a second motion, namely, the downward stroke of what is termed, the elevator; the water in the well, cistern, or what not, acting, if it has sufficient depth, and consequent resistancethe motion of the elevator being quick, as the piston-and this is the force pump operation. Now, I beg to ask in what does this differ from the common forcing pump? Why, in nothing but the substitution of water (without the slightest possible benefit accruing by it,) for the well-known ram; and here is Mr. Baddeley's "legerdemain"-two well-known operations to be performed, to obtain a result which either is capable, singly, of producing.

There are other disadvantages attending this "wonder-working" machine, which, in all probability, hereafter, I shall be required to exhibit.

I am, Sir, your most obedient servant, JAMES A. EMSLIE. Newcastle-upon-Tyne, April 2, 1842.

ABSTRACTS OF SPECIFICATIONS OF ENGLISH PATENTS RECENTLY ENROLLED.

BENJAMIN AINGWORTH, OF BIRMINGHAM, GENT., for improvements in the manufacture of buttons.-Rolls Chapel Office, April 7, 1842.

Six skins of parchment about buttons! To thread our way through them is no easy task, even with the aid of the admirably elaborate directions for threading given by the patentee-as hard, almost, as finding the

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