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him on the supposed principle of my furnace-"I have long paid great attention to the operation of smoke burning furnaces generally, and more particularly to those constructed on the principle so imperfectly attempted by Mr. Williams. " (And again, still having never seen a single furnace of my construction.) "This conviction has been forced upon me by a careful and unprejudiced examination, (careful and unprejudiced!) of a great many steam engine furnaces, erected both by myself and others, including several constructed by Mr. Williams himself." What, Sir, will honest, well meaning men say of such "careful and unprejudiced examination," seeing that when called on he was unable to point to a single one which could justify the slightest ground for the word "examination," and for the plainest of all reasons, namely, that none such were in existence at the time this (wisely undated) report was written.

For the sake of truth, however, and to do justice to Mr. Armstrong, I must state that he subsequently consented to a letter of recantation, and wrote to my agent, stating, among other things, as follows: "I find that the opinions expressed in my report before named, were formed on erroneous data, and therefore calculated to mislead. I therefore consider it due to the public and the inventor, and not less to yourselves, to make this explanatory statement, as I find my report has been misconstrued and circulated to your injury, and as you have expressed your satisfaction with this explanation, and agreed, at my request, to waive any legal proceedings in respect to such injury.'

This paper, my solicitor states, Mr. A. consented to sign, on three conditions, (dictated by himself,) one of which was,

that it is not to be published or circulated, but only referred to at the office of the solicitor." Having subsequently evaded the actual putting of his name to the paper, (as if that were of any importance, after having admitted its necessity and correctness,) I feel absolved from the restriction as to publication. The verbal admission of his error (and consent to sign,) was in fact as satisfactory as a writ

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PLATING BY ELECTRIC PRECIPITATION.

Sir, I see in No. 956 of your Magazine a letter from Mr. Walker, claiming certain improvements in the electrotype, for which patents have been taken out by others; but in my opinion, neither Mr. Walker, nor any other person has a right to take out a patent for either electro-plating or gilding, as the matter was made public by Mr. Sturgeon in his Annals of Electricity, very soon after the original discovery of the electrotype by Mr. Spencer, in a letter to that gentleman inserted in the work above mentioned. Mr. Sturgeon says in the letter referred to, "You will remember the idea occurred to me of giving medallions, coins, &c., taken by the process of voltaism, silver, or golden surfaces, by a similar voltaic process, employing a solution of either of those metals with the prepared matrix instead of a solution of copper.

From your obedient servant,

A COUNTRY SUBSCRIBER.

FENN'S REVOLVING OIL STONE. [Registered pursuant to Act of Parliament.] It frequently happens, that nearly as much skill is required in preparing and sharpening tools as in the subsequent use of them; and in the case of engravers in particular, success depends greatly upon the care bestowed upon the sharpening of their gravers. It is in many cases of the highest importance, that a precise angle should be maintained between the face and the belly of the tool, and the attainment of this desideratum by a backward and forward motion upon a stone lying in a horizontal plane, is a work requiring more than an ordinary degree of skill for its successful execution; a skill, in which those who possess it, justly pride themselves.

In order to obviate the greater portion of the difficulty which presents itself in the attainment of this object, Mr. Fenn, the well known tool-maker, of Newgatestreet, has registered an ingenious little contrivance which is shown in the annexed engraving, by means of which any artist, or amateur, may readily ensure a fine edge of the required form for his gravers. It consists of a small disc of turkey stone a, mounted upon a suitable holder and axle, which has a small pinion

THE SUPPOSED PERCUSSIVE ACTION OF STEAM.

on its outer end on the opposite side of the supporting side frame or bracket; a multiplying wheel b, furnished with a handle, takes into and drives the pinion. A small quantity of oil being spread

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on the surface of the revolving hone with a piece of woollen cloth, the tool is held against it at the required angle, and the stone made to revolve by turning the wheel b.

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THE SUPPOSED PERCUSSIVE ACTION OF STEAM.

Sir, Mr. Parkes appears to me to have fallen into an error which many other philosophers have done before him, viz., that of inquiring more into causes than effects. He imagines that, according to the recognised laws of expansion, a greater portion of work is performed by the Cornish pumping engines than the steam used would warrant us to expect; and without taking into consideration the possibility that his calculation of the effect produced may be erroneous, he sets off into the regions of fancy in

search of a cause: this cause he styles the "percussive action."

The first idea which the word "percussive" gives rise to is, that of the steam travelling through a partially vacuous space before it comes in contact with the piston, and acquiring through that motion a force similar to that acquired by any body in falling; or moving in any direction with a continuous propelling power applied to it. Such, however, cannot be the view taken of the subject by Mr. P., or he must obviously

be in error, as decidedly the reverse of percussive action is produced by so admitting the steam; for however rapidly a body of steam may flow into a partial vacuum, it must expand far more rapidly; and the outward portion, or that which falls on the piston first, will necessarily be attenuated in a great degree, and impart a force thereto little exceeding that of the partial vacuum which previously existed.

If, then, the travelling-if I may so speak of the steam gives diametrically the reverse of "percussive action," we shall gain a maximum of this imagined force when the vacuous space through which the steam has to travel, between the induction valve and the piston, is the smallest that can be obtained. This is so palpably plain, as to admit of no dispute on the subject; and yet, if Mr. P. admits it to be the case, his theory at once falls to the ground. Let us imagine, for instance, a cylinder having a piston fixed in any part of it. Above

this piston let us imagine a slide of inappreciable thickness, yet strong enough to bear the whole pressure of the steam, and placed so as not to touch the piston, yet at an inappreciable distance from it, and let the induction port be double or treble the usual size. Now, suppose the steam to be full on, and pressing on the slide with a force equal to 1,000 lbs., can we, without risking a charge of absurdity, imagine it possible that, by suddenly withdrawing the slide, the steam may be made to exert a force on the piston, exceeding that which it had previously exerted on the slide? If it would exert this extra force, whence comes it? The body of steam has not moved an appreciable distance, and consequently cannot have acquired an appreciable momentum; and I have just shown that, if it had moved, the reverse of percussive action must have resulted. This is so obvious, that I may be charged with prolixity in giving further illustration; nevertheless, I will say a word or two more.

If, by suddenly withdrawing the slide, the steam is made to exert a force of 1,500 lbs. on the piston, instead of 1,000 lbs., (the pressure it previously exerted on the slide,) the same, or nearly the same, effects must be produced on the parts of the cylinder submitted to the action of the steam; and, consequently, if a mercurial gauge were fixed a little

above the slide, and marked a pressure of 40 lbs., the mere abstraction of the slide would cause the quiescent mercury to rise suddenly, and mark a pressure of 60 lbs. ; and yet, all that we have done to the steam has been to substitute one base for another. If such an effect were possible, we may draw from it the most extravagant conclusions; for if a number of these cylinders, pistons, and slides were fixed directly to a boiler, the simple abstraction of one slide would suddenly raise the force in the boiler from 40 to 60; and if, at the precise moment when the steam was exerting this 60 lbs. force, another slide were suddenly withdrawn, the pressure would be raised to 90 lbs.; and if another were then withdrawn, it would be raised to 135 lbs. ; and so on ad infinitum. Your readers will, I doubt not, smile at the absurdity of such a calculation, but those who are inclined to weigh the matter, will find that the idea is arrived at by strictly inductive reasoning; and, absurd as it is, it must hold good, as long as this "percussive theory" does.

Such, or nearly such, were the ideas which occurred to me when this theory first came under my notice; but as I imagined Mr. Parkes advanced it merely as an opinion, I took no further notice of the subject. I find, however, from a subsequent paper of Mr. P.'s, that he still upholds his theory, and brings forward what he seems to consider indisputable arguments in its support.

I have not the abstract of his last paper by me at present, but, if I recollect right, he states that if a mercurial gauge be attached to the cylinder, the sudden impact of the steam will cause the mercury to rise high enough to denote a pressure of 60 lbs. per inch, when the pressure of the boiler is only 40 lbs.; and that when the steam is admitted gradually, no such effect is produced. I believe 40 to 60 are the proportions; but at all events we will assume it to be so, for the sake of round numbers. Mr. P. also states, that in the larger engines the cylinder covers are deflected, or bulged outwards, when the steam is admitted suddenly; but when slowly, no such effect is produced.

Now, to a merely casual observer, these two arguments seem to tell strongly in favour of the "percussive theory;" but when examined into, we find them to result from causes entirely independent

THE SUPPOSED PERCUSSIVE ACTION OF STEAM.

of an additional, or "percussive force." With regard to the first argument, I would ask, how can Mr. P., or any one else, imagine it possible that a stream of mercury driven 100 inches, with the great velocity it must acquire from having so great an unbalanced pressure on one side, would suddenly stop and remain quiescent, when it had risen a sufficient height to balance the pressure of the steam? The momentum acquired by such a velocity would be sufficient to carry the column considerably higher, even though the whole pressure of the steam were instantaneously removed when the gauge marked its proper level. What, then, ought to be the effect when this momentum is aided by the continued pressure of the steam? Theoretically, a body of mercury under such circumstances should rise to double the height warranted by the pressure of the steam; provided means were adopted to prevent the column acquiring additional length or weight after it had reached the 100. Practically, of course, such an effect cannot be obtained. The deflection of the cylinder cover is, apparently, a more weighty argument; but if analysed, is found to result from an entirely different cause to that assigned by Mr. P. Before, however, we investigate this point, I must request your readers to bear in mind, that in the engines Mr. P. experimented on, although the pressure of the boiler was about 100 inches of mercury, that of the steam in the cylinder was only about 75, with the steam full on; owing, of course, to the velocity of the piston being too great, or the induction too small to admit of the steam flowing in with sufficient rapidity.

Now, let us imagine an engine to be working under such circumstances, the piston at the top of the cylinder, and the steam admitted suddenly. The space between the cylinder cover and piston being small, in comparison to the size of the induction port, is almost instantly charged with steam of nearly equal pressure with that of the boiler; before this space can be enlarged, the vis inertia of the immense mass of matter, comprising the piston, beam, pump-rods, &c., and materials to be lifted, has to be overcome; and sufficient time will be required to do this, to admit of the pressure above the piston becoming equal to that of the boiler. This pressure is sufficient to

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bulge or force the cylinder cover outwards. As soon as the piston begins to move, the pressure gradually decreases from 100 to about 75, and the cylinder cover assumes its proper form. I need not enter into any elaborate argument to show why the cylinder cover is not deflected when the valve is opened slowly, as every one, who knows any thing of the steam-engine, knows there is a great loss of power occasioned by so admitting the steam-not owing to the loss of "percussive force," but owing to the wiredrawing and undue expansion, which is the natural result of admitting the steam too slowly.

If I am rightly informed, Mr. P. in his calculation of the effect produced by the Cornish engines, takes the maximum pressure of the steam in the cylinder at 27 lbs. ; which 27 lbs. is continued during one-sixth of the stroke, the steam being expanded during the remaining five-sixths. If this be his mode of proceeding, he is not likely to arrive at a just conclusion, as to the relative quantities of steam consumed and work done; as it is obvious that the steam is exerting a pressure nearly equal to that of the boiler at the commencement, when the piston is moving very slowly; which pressure decreases as the velocity of the piston increases, and consequently expansion is going on during the whole of the stroke, instead of only during fivesixths.

Not being thoroughly conversant with the action of Cornish engines, I should incur a risk of error in speaking thereon; therefore, I wish it to be borne in mind, that the following remarks on the crank are not made in reference to them. My reason for speaking on this subject is in reply to an assertion of Mr. Parkes, that a crank engine cannot possibly realize the advantages gained by a non-rotative; and I see by a reference to the patent list, that a patent has lately been taken for machinery to be used as a substitute for the crank, probably with a view to obviate the supposed disadvantages assigned to it by Mr. P. Now, as far as I can perceive, a pumping engine, regulated by a crank and fly-wheel, would realize more advantage than a non-rotative, especially while the latter labours under such a palpable disadvantage as the one Mr. Parkes experimented on, viz. not admitting the steam with suffi

cient rapidity to keep up a due pressure in the cylinder when the steam is full on. In a crank engine, the extreme slowness of the piston during the first part of the stroke, allows sufficient time for nearly the full pressure of the steam to be maintained in the cylinder; and consequently, much more may be admitted during one-eighth of the stroke, than Mr. P. obtained in one-sixth. I should imagine there would be considerable difficulty in arranging a merely reciprocating engine, in such a manner as to keep up a full pressure while the steam is on; as such a pressure cannot be maintained unless the piston is loaded so as to offer a certain modicum of resistance; and if the load be thus increased, the weak expanded steam at the end of the stroke will not be sufficient to keep the load in motion. With a crank and fly-wheel, both these disadvantages may be obviated: the slow motion of the piston at the commencement of the stroke, allowing the admission of nearly full pressure steam; and the momentum of the fly-wheel, acting, as it does, with a gradually increasing leverage from the middle of the stroke, admitting of the steam being expanded to any degree of rarity above that required to overcome the friction, &c. Yours, respectfully, J. BRITTEN.

ABSTRACTS OF SPECIFICATIONS OF ENGLISH PATENTS RECENTLY ENROLLED.

SIR SAMUEL BROWN, KNIGHT OF THE ROYAL HANOVERIAN GUELPHIC Order, COMMANDER IN HER MAJESTY'S NAVY, OF NETHERBYERS-HOUSE, AYTON, BERWICKSHIRE, for improvements in the means of drawing or moving carriages and other machinery along inclined planes, railways, &c., and for drawing or propelling vessels on canals, rivers, and other navigable waters. Enrolment Office, December 18, 1841.

The first part of this invention relates to a mode of propelling carriages by means of a ground chain. For this purpose a cranked axis, turning in suitable bearings upon the framing of the carriage, and driven by connecting-rods from the steam cylinder, carries a cog-wheel and a chain-wheel. Two other axes also carry respectively chain-wheels and cog-wheels, which are driven by the former. On motion being given to the machinery, a ground-chain is progressively picked up, and passing under the wheel on one axis and over

the other, is laid down again, and the car. riage thereby propelled along.

The second part of the invention consists in the application of similar machinery on board a vessel, for propelling it.

The claim is, 1. To a mode of propelling carriages by means of wheels or endless chains, worked by suitable gearing, and acting with a ground-chain; 2. To a mode of warping vessels by means of wheels or endless chains, worked by suitable gearing, and acting with a chain of single links, whereby one chain is rendered sufficient for the passage of vessels in opposite directions at the same time.

JAMES HENRY SHAW, OF CHARLOTTESTREET, BLACKFRIARS-ROAD, Jeweller, for improvements in setting wheat and other seeds.

1841.

Enrolment Office, December 18,

These improvements consist in furnishing means by which given quantities of wheat or other seeds may be set at regular intervals apart. A frame is mounted on two running wheels; two smaller wheels are also applied to side frames in front of the machine, which admit of adjustment, so as to regulate the depth of furrow produced by the ploughs, which are fixed in the front rail of the framing by wedges. On the nave of one of the running wheels a cog-wheel is fixed, which, by means of a clutch-box, can be thrown into or out of gear, with a corresponding cog-wheel on the axis of a seed cylinder. This cylinder is divided into a number of compartments, corresponding to the rows of seeds to be deposited. Around each compartment there is an apparatus for regulating the quantity of seed, and depositing it at the prescribed distances apart.

The seed passes down rectangular tubes, the lower ends of which are kept closed by spring valves, which are opened at proper intervals, and to a proper distance, by a series of curved bars affixed to the machine.

The claim is to combining mechanical apparatus into a machine, by applying depositing apparatus, and suitable parts connected therewith, to a revolving cylinder.

WILLIAM CHESTERMAN, OF BURFORD, OXFORD, GENTLEMAN, for improvements in filtering different liquids. Enrolment Office, December 21, 1841.

Under this deceptive title we are presented with another new coffee-pot, which seems to us to be an inferior modification of the very excellent contrivance of Mr. Platow.

This coffee-pot is made of tin plate, with a wooden handle attached horizontally to one side of it; a hole is made in the bottom of the vessel, to admit a heater to enter a tube which passes up the centre of the pot. The ground coffee being placed in the vessel,

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