present enlarged surfaces for mutual contact, and, consequently, enlarged surfaces for chemical action between the air and the gas.

I may now say a word as to the application. On this head, the experience of every practical man must satisfy him, that, as the forms, characters, and objects of furnaces differ, so must the situation and adaptation of the means of admitting and dividing the air be also varied; and it is not for a patentee to describe all possible modes or situations of application or adaptation. Again, as it is found by experience, that even the peculiar character of different kinds of fuel vary in the quantities and character of their gaseous formations, so will they vary as to the length of time required, or the difficulty in effecting the requisite mixing or diffusion of the gas with the air. Were it convenient, perhaps, the most effective mode of introducing the air and applying the principle would be, by extending the range of apertures along the entire roof and sides of furnaces, and even along the flues. In ordinary boilers, however, this would interfere with the situation of the water. In such, therefore, we are necessarily limited to the two ends of the furnace, and to these have I hitherto recommended the admission of the air to be confined in steam boilers.

In the case of reverberating furnaces, or those for heating large iron plates, a greater range is available; and here the orifices or apertures may be placed along the roof and sides, as well as at both ends.

As stated in my former communica. tion, the object and practical application of this patent is as well defined, and as distinguishable from others, as the Argand gas-burner, with its numerous apertures, would be from that with a single large jet. The only difference to be reconciled, in comparing the Argand lamp and the Argand furnace, is, that their respective actions have to be reversed, since it is the air which issues in a divided state, and by suitable apertures, to the body of the gas, in the latter; while in the former, it is the gas which issues in a divided state to the air-the object to be effected, however, being identical in both, namely, enlarged surface, or atomic contact and diffusion, to as great an extent, and as rapidly as possible. On this head, I need only repeat the observa

tion of Professor Brande, when he says, "the effect is exactly the same, only, in your furnace, you invert this ordinary state of things, and use a jet of air thrown into an atmosphere of inflammable gas." I am, Sir, &c., C. W. WILLIAMS.

Liverpool, December 22, 1842.

WOOD PAVING-COL. MACERONE'S FLYING STONE DRIVER-WATERPROOF COMPOSITIONS-FILTRATION-LIGHTNING CON

DUCTORS, ETC.

Sir,-In your No. 1006 there is a letter on wood pavement, by "Junius Redivivus," cogent, as are all from him, but which requires a remark or two from me. He says, or implies, that my suggestion and remarks on wood pavements appeared in 1833, whereas, the work he alludes to was only a second edition of that printed in 1824. "Junius" also forgets to mention my plan of mere mechanical pressure on the subsoil, and then upon the wood or stones. The machine to perform this office in the most brief and effectual manner, you, Mr. Editor, have christened by the name of the "flying stone driver;" and you judiciously add that, whether the pavement be of wood or stone, my plan is by far the most effective and economical. In fact, any person of common sense, who will observe and reflect, cannot but arrive at the intimate conviction, that all the complicated, tedious, vastly expensive processes of laying gravel, broken granite, or concrete, under the wood or stones, and then grouting, are utterly useless, supererogatory, and inconvenient, compared with my merely mechanical, cheap, and perpetually enduring plan, by which the pavement must necessarily become more dense and level the longer it is used. All this I have demonstrated in my pamphlet called "Hints to Paviours," and in many articles in your Magazine, particularly, I think, in 1838. As many of your readers of the present day may not have seen my said work or letters, I hope you will allow me to reiterate a mere outline of my system, and patent machine. construct a square or circular horizontal frame of wood, six or eight feet diameter, mounted upon four or more castor wheels, which turn in every direction. Upon this frame are mounted two upright square spars, exactly like those of a pile driver, but only ten feet high, or less. At the top of these spar guides is a grooved pulley wheel, at least a foot in diameter, over which passes a rope, to the lower end of which is attached a block of wood strongly hooped with iron, similar to a butcher's large block, which

I

In

may be either square or fround. In the centre of the basement frame is a hole for the block to fall through. Six or eight men standing round the circumference of the stage, simultaneously pull up the weighty block by as many ropes attached to the top of the main one, then suddenly letting go, the block falls with a great momentum on the substratum to be compressed, and afterwards on the stone or wooden pavement. After two such powerful compressions, it must be passing strange indeed if a perfectly level surface is not preserved, maugre the rolling of the heaviest wagons; but should any inequalities appear, the protuberances alone must be attacked by my machine, and there is your pavement fixed for ever. the case of having to take up any part to lay water or gas pipes, the machine will, in a few strokes, restore it to an equal density with the rest. A watering cart will indicate the least protuberances to be knocked down. One of my declared and obvious objects has been economy, in making a perfect pavement with the stones already in use. But the paviours have, for years past, been persuading the lieges to have new stones, and larger and larger, which, notwithstanding all the fuss of gravel, then granite, then compost, then grouting, have produced pavements in Cheapside, the Strand, Holborn, Oxford-street, &c., which, after a few days, became as even as the surface of the Thames in a gale of wind! But then-hurra!-the job has had to be done over again in a few months, besides the constant picking up of holes, &c. " Junius" recommends the wooden blocks to be laid at an angle of 45°. I do not see the utility of that. Square blocks

are more simple and cheap. The grooves cut on the heads can only serve as deposits for wet and mud. The surface grouting when set, must soon be reduced to powder, whether between wood or stone, by the vibration of the carriage wheels. In 1824, in writing on wood pavements, I recommended hot coal tar to be poured over the surface when dry. I leave you, Mr. Editor, and your readers, to reflect on this. But durability is, perhaps, no object with the paviours. It would require a pamphlet to point out the egregious errors of the present and past systems of paving; so I must be content with these brief and disjointed remarks, which, notwithstanding the importance of good, cheap street paving, will, I know, be no more attended to by the paving and paying people than they have been during the last eighteen years.

In your last Number I read a letter of your intelligent and benevolent correspondent Mr. Wm. Baddeley, in which he kindly eulogises my cheap mode of preserving boots and shoes, and keeping out the wet.

He

also mentions an" "improved" method of applying my simple waterproof composition, thought of by your agent at Hamburgh; that is, of pouring the hot melted composition into the inside of the boot, &c. I have applied that method to my own boots and shoes for the last thirty years; but when I have ventured to do so by the boots and shoes of my wife and children, they have made an outcry about its soiling their stockings, and resisted my touching them at all. But I would beg Mr. Baddeley to remember that a very important part of a boot's construction is the external sewing of the sole to the welt, and there it is that an abundant application of the hot composition is to be poured in. If a bright polish is desirable immediately, a solution of bees'-wax in spirits of turpentine, subsequently applied externally, and suffered to dry for a day or two, will provide it. Whilst shooting or fishing in the Pontine marshes, and the other maremme, or sea side marshes, of the Mediterranean, we use "swamp boots," which draw up to the "fork" of the thighs. The shooters, and fishers, and sportsmen there, grease them with lard. So did I; but I soon found that this coating became rancid, and rotted both the leather and the sewing. Hence, in 1807, I added the powerful antiseptics, rosin and wax, and found a vast difference in all the results. I often stop to advise labourers in the streets to keep their feet dry, and make their shoes endure thrice the usual time by so cheap an application. Many, many such have subsequently thanked

me.

Three pairs of boots properly so treated, have lasted me five years.

Mr. Baddeley is quite correct in his statement of the power of a small admixture of rosin with the oil, preventing the oxidation of the brass or copper works of machines to which it is applied. Several engineers have adopted this my suggestion many years ago, and found it to answer.

Mr. Baddeley humanely and kindly asks why the wood paving gentlemen do not present me with some sum of money in consideration of my older and continued advocacy of wood paving? Alas! I have told them how I could lay down their pavements at one-fourth of what they now cost. But the sequel is, nothing! The stone paviours say that, without the continual renewal of the pavements, and the new stones, their "occupation's gone." They will not see that their contracts for "keeping in repair" could, by my means, be fulfilled at one-tenth or less of the cost of digging up, relaying, &c.

To return, for a line or two, to my simple application to boots and shoes, I must state that, when, about two years ago, I fell into want through the suicide of my last

steam carriage company, I felt anxious to obtain any employment. I knew that I could do good service at Woolwich; but how to obtain any patronage or introduction? So I wrote to Lord Hill, offering to render all the shoes and boots of the army, or any part of it, waterproof, and thrice as durable, at twopence a pair. I also proposed to render any portion of the parade behind the Horse Guards, whereon the troops tramp in the wet in rainy weather, as dry and hard as a marble pavement, at twopence a yard square, by merely pouring over it, when dry, hot coal tar, as I had done to the garden walks of Mr. J. R. Bell, at Blackheath, in 1816, and which endure to this day,-the prototype of all bituminous roads. "Lord Hill presents his compliments to Colonel Macerone, but cannot give him any employment!" Here you see, Mr. Baddeley, was a stopper to my waterproofing proposal, and to my twenty-seven years old bituminous surface. A Frenchman named Polonceau immediately obtained a contract to treat the paths along Whitehall and Parliament-street with the same bituminous application, at ten times the price which I had proposed to Lord Hill.

Now I have my pen in my hand, a word on the filtration of water, which subject has lately been much mooted in the Mechanics' Magazine, and other periodicals. I do not understand, from all that I have read, that any filtration is thought of, but that of freeing the water from all impurities which are mechanically suspended in it; such as is well performed by sandstone filters called "dripstones." Now it is of the utmost Importance that the benevolent men who advocate the filtration of our filthy, putrid Thames water, should seriously bear in mind, that mere mechanical filtration and chemical filtration are very different things. Any salt, or other substance perfectly soluble in water-for example, salt or white sugar-will pass through the dripstone filter as well as the purest water. But not so with the chemical filter, of which I will give an instance.

My friend Giovanni Dall' Armi, who introduced into Italy and France the art of lithography, in 1806 or 1807, constructed, in 1808, a chemical filter, composed of a cask with a perforated diaphragm, over which was laid a thick stratum of pounded charcoal, and over that a layer of sand; then broken bricks, then a large sponge, or thick haircloth. On the 27th of September, 1813, I attended an experiment made at the hospital called "Degli Incurabili," at Naples. In this place there were several stone cisterns to macerate skeletons, so as to clean the bones. Each cistern contained two or three skeletons, and the water had become brown

and putrid. The investigating party consisted of the celebrated physician Cotugno, Bruno di Amantea, Angelo della Leonessa, Sementini, the Prince Colonna, the Duke of Cassano Serra, and my co-pupil Don Michelino Serra. A portion of the foetid water was put into the charcoal filter of Dall' Armi, and, after it had passed through it, the entire party sipped it from a goblet, in which it was as clear as crystal, and equal in taste to the best spring water, barring the flatness which generally belongs to filtered water, from the deprivation of the air it previously held in solution.

Lightning conductors have recently been brought into notice because of the injury to St. Martin's church steeple, and the ignition of two ships by the electric fluid. On this subject I really do not know what to say. If people have not listened to the demonstrations and warnings of the great Benjamin Franklin, how can I expect that my feeble voice, repeated and re-echoed as it may be, will ever be heeded? But, as "facts are stubborn things," I will mention one or two for the consideration of your intellectual readers. When I happened to be at Rome in 1811, I found that St. Peter's Church, isolated in a vast plain, was very frequently struck by lightning, during the thunder storms which are so frequent there in November and December. I was acquainted with General Miolis, the imperial governor of Rome, with the Count Norvince de Monbreton, minister of police; M. Forbin Janson, inspector of the museums, &c., and induced them to form themselves into a committee of investigation. I had seen how the copper ball had been riddled by the lightning, and several great stone steps dislocated and cast abroad. The process of these electrical actions induced the French authorities of Rome to place conductors all over the church; one fifteen feet above the cross, with a point of pure gold, and others at every angle of the edifice. They were all above an inch in diameter, and supported by perforated pieces of marble let into the walls. It is a great increase of efficacy in lightning conductors for them to have their summits terminate in many points instead of one. Such will generally draw off the electric fluid quite silently, without any discharge or perceptible corruscation. If a branch of heath, broom, or a common birch broom, be approximated to the most powerful and fully charged electric machine, all the electric fluid will be drawn off quite imperceptibly. Thus it is that the cypress, the laurel, and some other trees, have been deemed "sacred," and lightning-proof, by the ancients, because their innumerable sharp pointed leaves prevent any electric discharge. Electricity is the main supporter

of vegetable life; in some cases, I am convinced that it is the only one; whereas, in some of the lower orders, such as the Parasiti and the Fungi, it seems to be less needed. In the "lower orders" I do not include the Gramminæ, which, I could show, are highly affected by the electrical state of the atmosphere. But this disquisition is not to my present purpose, and would lead me to a great length of disquisition, which I shall detail in my continuation (if I live) of the "Electrical Theory of the Universe," three papers on which appeared long ago in your omni-important miscellany.

I have the honour to be, Sir,
Your obedient servant,

F. MACERONE.

P.S. Tubes form better conductors than solid bars, because they have two surfaces. The conductors in this country are not onetenth of the proper size. Ships should have chains proceeding down the shrouds into the water.

THE INVENTION OF STEAM DREDGING, AND THE LATE RICHARD TREVETHICK.

Sir,-As considerable doubt still hangs over the first application of steam to dredging purposes, I send you a few particulars which will throw some light upon the share which the celebrated Richard Trevethick had in this work. These particulars, it must be admitted, are not so satisfactory as could be wished; but, considering the obscurity which is thrown round the origin of this invention by all the writers in the Encyclopædias and other standard works, any contribution to the very scanty information which is already published on the subject will, I think, be interesting to your read

ers.

The particulars I have to furnish are contained in the following extracts from a letter written by Mr. Edward Biggs, of Igtham, in Kent, who was for many years the principal manager of the extensive dredging operations carried on by the late John Hughes, in the river Thames, for the Corporation of the Trinity House, the East and West India Dock Companies, and other public bodies. I am your obedient servant,

AN ENQUIRER.

Extract from Mr. Bigg's Letter. "In the year 1806, I erected a steam engine on board the ballast lighter Brunswick, burden 60 tons, for Messrs. Hughes, Bough, and Mills, which was employed to deepen the river Thames, at the East India Moor

ings, Blackwall; and in the early part of 1807, my late friend, Mr. Richard Trevethick, came on board and looked at the machine, and was afterwards engaged by Messrs. Hughes to erect a dredging engine on board the Blazer gun-brig, a vessel about five-times the burden of the Brunswick. When it was finished, or, as it was then thought to be, Mr. Hughes, the late Mr. D. Vaux, engineer of the City Canal, and Mr. Mills, came to me on board the Brunswick, at the East India moorings, and informed me that the Blazer dredging engine was defective in some parts of its machinery, as it could not perform the work it was intended to do. They then wished me to go on board the Blazer and examine it, but I strongly objected, saying, I did not like to interfere with any other person's business; Mr Hughes then said that if I would not go on board to see what was wrong, the vessel must be put into Perry and Wells' dock, as it was a great expense to keep her on the river with two sets of men, when she was scarcely doing any work. Mr. Hughes then showed me a calculation of the expense of the Blazer dredging engine, and pressed me very much to go on board and make the necessary alterations, and I then complied with his request. The Blazer was after that time employed in finishing Mr. Hughes' work at the East India moorings, and afterwards for raising gravel near Westminster Bridge, at the entrance to the docks, and at various other places in the river.

"Mr. Trevethick was also engaged by Messrs. Hughes at the same time, to erect a dredging machine on board the Plymouth bomb brig, lying at Limehouse Hole; but when they found the Blazer engine defective, they requested me to go on board the Plymouth, and make a report to them on the subject, which I did; and then the boiler, engine, framing, &c., were taken out of the vessel immediately. Messrs. Hunter and English, of Bow, were then employed to erect a dredging machine on board the Plymouth, which vessel was first set to work to good effect, at Woolwich Dockyard.

"If my late friend Mr. Richard Trevethick, were now alive, he would, I know, assent to every word I have written on this subject. For several years before Mr. Trevethick left England to go to South America, we were very friendly indeed; he frequently coming to the works where I was engaged, and whenever I could spare time I used to spend a day very pleasantly with him in London; he pressed me very much to go with him to South America.

"Mr. Trevethick was a very ready clever mechanic; he died a few years ago at Dartford, in Kent, 13 miles from this place. "The late Mr. Rennie, and the late James

Watt, came on board the Brunswick in 1807, and they afterwards built a dredging engine for the fens in Lincolnshire."

MR. DREDGE'S SYSTEM OF BUILDING SUSPENSION BRIDGES.

Sir, I am particularly obliged to you for the able vindication of my claims in your notice last week of Professor Moseley's "Mechanical Principles of Engineering and Architecture," the more so, as but for that, I might not have known there had been any occasion for it, not having seen the work itself. Your remarks may probably seem to render any thing from me unnecessary; yet, nevertheless, I will venture to say a few words, for which, perhaps, you will allow a space in your Journal. As I am still without the advantage of having seen the Professor's work, all my present information must be considered derived from your review.

From this, it appears that Mr. Moseley "has demonstrated that it is false in principle to have a uniform section of iron for the chains of a suspension bridge, and that if it is required to build a bridge of uniform strength, and therefore, with the greatest economy of material, the area of the section of the chains should increase from the lowest point towards the main points of suspension." It also appears, that the Professor is very particular in pointing out in his Preface, that this beautifully simple principle is introduced for the first time.

As far as his demonstration of the fallacy of the old principle of suspension goes, I thank him for the trouble he has taken; because, just so far as his formulæ are correct, just so much is he assisting me in establishing my views on the subject. But, he may rest assured, he will find very few, if any persons ready to give him that credit he so anxiously seeks, for introducing a principle which was mooted and made public before his book was written, or indeed "thought of;" for, notwithstanding the Professor's assertion in his Preface, I deny that he has the slightest claim to any merit for that which I alone invented and introduced. I do not suppose that Mr. Moseley wishes his readers to think him the inventor of the principle he describes: I therefore request, and in common fairness have a right to expect, that he will state whether or not he has ever seen this principle of suspension carried out in practice, or any description of it, but such as has come either directly or indirectly from me? Or whether he thinks the varying section of the chains, and the use of the oblique rods, were ever thought of until I put them in practice across the Avon, at Bath? If he can trace his information to

other sources than myself, I will thank him to do so. If he cannot, why then, as a necessary consequence, I being a stranger to Mr. M., must have made the subject public before it could have come to his knowledge.

There is another point I shall just notice. The note, runs thus:

"This yariation of the section of the chains is exhibited in a suspension bridge recently invented by Mr. Dredge, and appears to constitute the whole merit of his invention.”

I will

The careful reader will at once perceive that Professor Moseley here allows my invention to be all he before demonstrates to be so beautiful and essential in suspension bridges; but he will also see that he does it with a bad grace, wishing to conceal the merit of the inventor as much as possible from the observation of his readers. not attempt, for I cannot divine his reason for such conduct, unless it is to arrogate to himself, by borrowing and building on other men's ideas, a merit that is not his own. But of this meanness, without sufficient cause, I would not willingly accuse any man, nor will I Mr. Moseley until I have seen his work.

Before I conclude, I beg to inform Mr. Moseley, however, that the. tapering the suspension chains is not the only merit I claim for my invention. So far from that being the case, a variation in the section of the chains is merely a consequence of that part in which the chief merit lies. What I allude to is the arranging of the suspending rods, which I place in an oblique instead of a vertical direction, with respect to the horizon. This it is which has all along bothered so many of the mathematicians and engineers, and this it is alone which allows me to taper the chains of a suspension bridge to the extent I propose, and have carried out so repeatedly in practice. If Mr. Moseley has not taken the effect of these rods into his calculations, I fear I shall not receive that assistance from the Professor's labours I at first calculated upon.

Let me request of Mr. Moseley to come forward and establish the position he has taken in his work, and, by so doing, disprove mine; and I hope he will have a sufficient regard for his reputation as a man of science to clear it from all appearance of the stigma which the borrowing of another's ideas, without a sufficient acknowledgment, would infallibly cast upon it.

I am, your obedient humble servant,
J. DREDGE.

[We regret the warmth with which Mr. Dredge expresses himself; but, at the same time, we cannot but feel that it has its exProfessor Moseley will no doubt do what is right in the matter.-Ed. M. M.]

cuse.