Sir, I must request your readers will do me the favour to substitute the word attraction for pressure in the thirty-first line from the top, page 424, vol. xi.

The apparatus consisted of a piece of board, a part of which is shewn at A, long enough to rest on the top of a tub, to which was fixed perpendicularly, a piece of square wood B, on which the guides a and b were fixed by wedges; and also the piece of wood c, for hanging the weights to. The weights were of lead, turned true, and suspended by a thread from the centre. They hung on the wire d, which, on being withdrawn, let them drop without shaking them. E is a cylindrical piece of wood, a portion of which is cut away at the upper part to allow the guide a to pass through it; E is kept upright by two pieces of wire working in the guide a, and one piece working in the guide b. A small piece of cork,

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, put on to one of the wires so as to slip easily upon it, completes the whole; this was for the purpose of measuring the distance to which the fall of the weight sunk E; the cork being placed as shewn in the drawing was stopped by the guide a, when Ë moved down, therefore, the wire passed through the cork; which, sticking to it, shewed the greatest depression of E.

It is to be observed that it was not requisite to ascertain the exact depression of E, as the experiments were only intended to prove the error of a conclusion already formed; and not to constitute the basis of a theory.

The tub was filled with water and the height at which E stood marked; ten ounces were then laid on the top of E which sunk it five inches and three-eighths deeper. A weight of five ounces was then suspended so that the bottom of it was six inches and three-eighths clear of the top of E.

The experiments were repeated with a three, a two, and a one ounce weight. When either of them fell six inches and three-eighths, it sunk the cylinder E to the same depth as twice its weight laid upon E sunk it, and no deeper; but they settled steadily upon E. When either of these weights were allowed to fall only one and a quarter inch, they sunk the cylinder E to the same depth, within about an eighth of an inch as when they fell six inches and threeeighths.

Now, if we estimate the force of a falling body from these experiments, which of them shall we take from which to calculate that force? The fall of only one-sixteenth of an inch has an equal claim with the fall of six inches and three-eighths, and yet,

what widely different results they will give. But the fact is, that of all the methods that have been imagined, to measure percussive force by experiment, those depending on the depression of a floating body by the fall of another body upon it, are the very worst, and it is a pity that scientific men should be so unthinking as to lead practical men to place any dependance upon them. Carelessness of this kind only serves to increase the contempt which one class feels for the other, a feeling which every one must deplore who is solicitous for the improvement of the arts.

But the error may be shewn in a readier way. A body before it has fallen one inch acquires a velocity of twenty-seven inches per second. The force of such a body is equal to that

of a body nine times its weight moving at the rate of three inches per second. And the force of a body in motion, although that motion be ever so slow, is greater than the force of its dead weight, which is easily proved either by reasoning or experiment.

In the same simple, cheap, and easy manner might the principles be put to the test upon which all those new inventions and new schemes depend, for which we see patents daily obtained, and money daily wasted; for in too many cases they turn out completely useless and unprofitable.

As some of your correspodents may perhaps amuse themselves by explaining why the five ounce weight with a fall of one sixteenth of an inch sunk the body E seventy-eight sixteenths of an inch, while the fall of one hundred and two, only sunk the same body eighty-six, I shall not at present attempt to account for it.

I am, Sir,
Your's respectfully,

S. Y., A Young Engineer.

Aug. 26, 1829.

P. S.-I know nothing whatever of the description of an engine to which Mr. Jarvis alludes, said to be signed S. Y.

THE NEW FLEET MARKET.

Sir, I trust to your sense of justice for the prompt insertion of a few remarks in vindication of the New Fleet Market from the strictures of the writer of the Rough (coarse would have been the more appropriate word) Notes in your last Number.

The chief fault your Correspondent finds with the market is, that the principal entrance was not made at the bottom instead of the side of the inclined plane. But he has wilfully overlooked the fact, that the greater part of the bottom of the plane in question is occupied by houses fronting the Old Fleet Market, the purchase of which would have added immensely and unnecessarily to the expense the Corporation have been at to obtain a clear space for the market. Was the architect to blame for this?

Another fault he finds is, that the shops on two sides do not look into the square of the market. But suppose it should turn out that orders were given to study the security of the occupants of the shops, in preference to any thing

else? Would the architect be to blame in this instance more than the other?

The shops have no openings externally (the gratings at the top excepted) either on the side of the market square, or on any other side; they consist of double ranges, with open fronts facing each other, but blocked up behind; and the access is by gates at different parts, the closing of which at night will effectually exclude those crowds of thieves and vagrants, who were wont to make Fleet Market their nightly rendezvous.

The clock-tower does not please your Note-taker: but chacun à son gout; he does not like it; I do. Who is to decide?

The key-stone of the gateway fronting the Old Fleet Market is said to obtrude itself to no purpose (something like the Rough Note-taker's remarks.) Now, so far is this from being true, that fifty instances from this very metropolis might be adduced of key-stones obtruding in the same way. To go no farther, Sir, than your own neighbourhood, I need only refer to Temple Bar, (a work of Sir Christopher Wren's) where an ornamental curved key-stone may be seen projecting quite as much as this of the New Fleet Market, and supporting just as little. I am, Sir, Sept. 13, 1829.

Your obedient servant,

CIVIS.

[Having referred the preceding letter to the author of the Rough Notes, he has favoured us with the following reply.-ED. M. M.]

"This by his voice should be a Montague, Fetch me my rapier, boy."-SHAKSPEARE. Dear Sir, I am obliged to you for your early communication to me of Civis's letter. Publish it by all means, but have the goodness, when you do so, to publish at the same time this my reply:

I confess, I did overlook (though not "wilfully") the fact, that the greater part of the bottom of the plane in question is occupied by still unpurchased buildings. Of course, we must transfer to the Corporation the blame which we have imputed to their travelled architect, for not making the entrance to the market where it ought to have been. But since the architect could not have an entrance at the bottom of the plane, why did he not get rid of the plane altogether? It would have cost but the expense of removing so many more cart-loads of rubbish to reduce the ground to one level, and of one level it ought unquestionably to have been.

The idea of blocking up the shops for "security" sake, is one which certainly did not occur to me. Deplorable as we all know the state of the police of the metropolis to be, one could hardly have imagined that it had reached to such a pitch, that people must be built in to secure them effectually from depredation!

"Chacun à son gout." Doubtless! But every one's taste is not a pure taste. There is a classical taste, and a barbarous taste; a Grecian taste and a Wapping Old Stairs or Low Dutch taste. Civis asks, "Who is to decide?" He ought rather to have asked, "Who is there to approve?" The very drovers laugh at the new clock-tower as they pass, and insist that it is not half so fine (which is the truth) as the clock turret of the Old Market.

Civis affirms that " fifty instances from this very metropolis might be adduced of key-stones obtruding in the same way," as the one in the gateway of this market. I defy him to produce one from any building of authority in matters of this sort. His reference to Temple Bar is singularly unfortunate. It is true, that on the side of this gateway next the city, there is a key-stone of a scroll-shape, which at the present time supports nothing; but had Civis examined the edifice a little more closely, and compared the inside with the outside of the gate, he would have discovered, that it originally supported an armorial shield, which has in the course of time fallen down.

I remain, dear Sir, Your's, &c.

The Author of the "Rough Notes." Sept. 14, 1829.

JACKSON'S PATENT STUDS.

"If the Patent Stud-Maker would screw in that part of his stud that he intends to force into the leather, he would certainly improve his invention; for if one of the studs which he describes in your Number, were to come out, it would make a complete thoroughfare to the foot. I have tried a common screw many a time, and it answers the purpose very well; if the materials would last it would never come out."-Extract from the Letter of a Correspondent.

Our correspondent seems to have overlooked, not only that screws would cost a great deal more, but that it would require ten times the labour to insert them. The stud is meant to effect

the same purpose as a screw in an easier way; and, for our own parts, we have no doubt of its retaining its hold equally well. We are glad to learn, that since the appearance of our notice on the subject, orders have been given at the Horse Guards for a trial being made of the stud, preparatory to its general introduction into the army. -EDIT.

ORGAN FOR THREE PERFORMERS.

Messrs. Flight and Robson, the builders of the celebrated Apollonicon, have just completed for Sir R. Vivian, an organ of a very novel and much-improved construction. While most organs have one, two, or, at the most, three sets of keys, this has no less than five; three in front, one above the other, and one on each side; so that three performers may play on the instrument at the same time, and all in perfect unison. The mechanism, on which the swell depends -the most difficult part by far of organ building has here been so skilfully contrived, as to give the players a perfect mastery of the gradations of tone, free from any of those sudden bursts which are so commonly characteristic of inferior instruments. The pedals are of the compound description, invented by Mr. Flight, and described in our 238th Number, p. 101; an invention, by the bye, which we have lately seen very unfairly ascribed to the Germans. A first trial of this organ was made last week by Mr. Adams in the presence of a select party of competent judges, when it appeared to give the most unqualified satisfaction. .D.

SOLVENT FOR PUTTY.

Sir,-In answer to an inquiry in your valuable Magazine for the best solvent to take off old putty from glazed sashes, I send you the following recipe :--Take American pearl-ash and mix it with slaked stone-burnt lime, to the consistency of paint, and apply the same until you find the strength of the putty is drawn out. The greatest difficulty is to get it to enter the bedding putty, which must be done over with the solvent oftener than any other part. The same solvent will prevent the necessity of burning off paint, as if applied with a brush over the whole surface, it soon destroys the tenacity of the paint. Your s, &c.

PETRUS.