and minutely examined. These essential matters being disposed of, the form and number of the arches and piers are the next things to be attended to. In the design for a bridge not less than 5 drawings are necessary, independent of minor details. The principal drawings are as follows:1. a plan of the piers and abutments at the lowest part of the foundation; 2. the superstructure, or roadway; 3 and 4. longitudinal and transverse sections; and 5. a general elevation.

Mr.

Before treating of these things, independently of each other, I shall just notice a peculiar feature in the ancient practice of bridge-building, namely, the erection of a chapel in the centre of the bridge. I believe it is pretty generally known, that the care of these bridges devolved on the priests, whence they derived the honorary title of "Pontifices."* Priestly influence is strikingly apparent in the designs of many of the most ancient of these structures; in the old triangular bridge at Croyland, for example, which was made to assume that form in honour of the Trinity. Hawkesmoor, in his "History of London Bridge," edit. 1738, has thus attempted to account for the grand pier" on which the chapel that formerly occupied the centre of the bridge was erected:-"To be a steadying for the whole machine, instead of making an angle, as it is in the famous bridge of Pragué, and in some of the bridges in France, so this fortress was placed in the middle of the bridge to stem the violence of the floods, ice, and all other accidents that might be forced against it." The idea of creating a stoppage in the centre of the current of a large river for the purpose of giving additional stability to a bridge, is certainly whimsical enough. Is it not more likely this pier was erected in the centre of the river for the purpose building the bridge in two distinct parts for the sake of greater security while the work was in progress?

of

I will now return to the important consideration of the preparatory mea

These buildings were afterwards in the care of the Emperors, and it was also considered an act of charity and piety to build a bridge.

Britton's Arch. Antiq. of England, vol, iv,

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sures for the progress of bridge-works. In the same manner as station-poles are fixed for the line of a new street, so should piles be driven into the bed of the river, and along the intended line forming the centre line of the new works. Along this line and between the piles, soundings are taken as often as the necessity of the work may require, and the boring-machine is as frequently used to discover the nature of the soil. If this is concluded in a satisfactory manner, the foundations of the piers may be then commenced. The reader has been informed of the method employed for this purpose in some of the most ancient stone bridges, called building on stilts: a full account of this method is also given by Scamozzi. Several other means have been at different times empleyed for this purpose: such as having the foundation erected upon rafts of sound timber of heavy scantling, and allowing it to be gradually sunk at the intended spot, properly guided by ropes, &c. ; or by turning the course of the river, thereby leaving the bed perfectly dry; or, lastly, by the improved methods of founding in caissons or coffer-dams. Westminster and Blackfriars Bridges are instances of the caisson method; Waterloo and new London Bridges of the cofferdam. As these edifices fully exhibit the progressive increase in the size of stone arches-in fact, from those of moderate dimensions to the largest stone arch in existence-I shall be the more circumstantial in describing the modes of their construction.-A coffer-dam is a space in a river surrounded by large pieces of timber of a certain form, called piles, placed or driven close together by a steamengine, or any other adequate power. The water is withdrawn from between the surrounded space, in order that the pier may be erected on dry ground. Pileing is of various denominations: close-pileing (for embankments), ground-pileing, plank-pileing, &c. are the terms and varieties in common The close-pileing (see figs. 2 and 3) is executed by driving two piles at a distance apart; and these are connected together by bolting pieces of timber to them longitudinally, technically termed wailing

use.

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pieces. Grooved and plank-pileing is executed by grooving the piles, and introducing a plank of timber into the grooves thus:

This method gives great neatness to the dam, and generally supersedes the necessity of puddling with clay; it is not, however, remarkable for security. The lower ends of all piles are sharpened or cut into a pyramidal form, and shod with iron; the upper extremities are encompassed with a ring of the same metal, to prevent their splitting by the force of the iron ram with which they are driven into the earth. As soon as the pier is completed, these piles forming the dam are withdrawn. The timber generally employed is either oak, elm, or beech. The coffer-dams of new London Bridge were of an elliptical form, and consisted of three rows of piles dressed in the joints (without grooving): some of them measured between 80 and 90 feet; and they were all puddled with clay, &c. and shod with iron.

The foundations of the piers are raised upon piles of beech wood, on the heads of which were laid two rows of sleepers, 12 x 12, covered with level planking, six inches thick.

In order to compensate for the additional obstruction which the works of the new bridge, while in the progress of erection, would occasion to the navigation of the river, it was determined that, previously to proceeding therewith, two of the small arches of the old bridge on each side should be thrown into one, by which means freer scope would be given to the current. In the accomplishment of a conversion of this kind, more skill is required than might at first sight be supposed. It became necessary for the purpose to board in and take up half the roadway at a time, and to clear away for the reception of an iron girder A, (fig. 1) and massive timber principals BB; also to place what may not be inaptly termed the brest-summer C. The principals have a purchase on the girder, as may

be seen from the engraving; and, instead of being placed at intervals, as in roofs, they are all fixed and bolted close together from one end of the roadway to the other, forming a complete unbroken mass of timber. On the brest-summer, at intervals, pieces of timber are mortised in forming joists, or purloins D DD, on which substantial planking is fixed, the road being paved as before. These are further strengthened by counter-principals; some of the struts being fixed close together, and others having an interval of one width between them. It will be seen that the greatest precaution was necessary in the construction, owing to the bulky and weighty materials continually passing over the bridge from the hop-market, tanners, and merchants' wharfs, which are situated contiguous to the building. Another difficulty laboured under was to keep the truss sufficiently high to allow of vessels to pass under; in doing this, the span became exceedingly flat, and added to the difficulty of forming the centering. On the whole, this may be reckoned a good specimen of professional and mechanical skill.

The contractors for the execution of these alterations in the old bridge, and for the building of the new bridge, were Messrs. Joliffe and Banks. For the former they were to receive 30,000l.; for the latter, 426,000l. The time allowed was six years.

On the 27th of April, 1825, the first coffer-dam above described was finished, and the water pumped out; and on the 15th of June following, the first stone was laid by the then lord mayor, Alderman John Garratt. The depositum plate, which was of brass, had the following inscription engraved upon it in Latin and in English. I shall conclude the present paper by subjoining the latter. It is from the pen of Dr. Coplestone, Bishop of Llandaff and Dean of St. Paul's.

THE INSCRIPTION.

"The free course of the river being obstructed by the numerous piers of the ancient bridge, and the passage of boats and vessels through the narrow channels being often attended with danger and loss of life, by reason of the force and rapidity of the current; the CITY OF

LONDON, desirous of providing a remedy for this evil, and at the same time consulting the convenience of commerce in this vast emporium of all nations, under the sanction and with the liberal aid of Parliament, resolved to erect a bridge upon the foundation altogether new, with arches of a wider span, and of a character corresponding to the dignity and importance of this royal city nor does any other time seem to be more suitable for such an undertaking than when, in a period of universal peace, THE BRITISH EMPIRE flourishing in glory, wealth, population, and domestic union, is governed by a Prince, the patron and encourager of arts, under whose auspices the metropolis has been daily advancing in elegance and splendour. The first stone of this work was laid by JOHN GARRATT, Esq. Lord Mayor, on the 15th day of June, in the sixth year of KING GEORGE THE FOURTH, and in the year of our Lord 1825; RENNIE, F. R. S. Architect.'

JOHN

ANDERSON AND JAMES'S LOCOMOTIVE

CARRIAGE.

Sir,-The want of sufficient time has hitherto prevented my calling your attention to some little errors, into which you have inadvertently fallen, in your account of Messrs. Sir James Anderson and W. H. James's steam-carriage, arising probably from the paucity of information contained in my descriptive sketch of that machine. In reference to an undeserved compliment you paid to me at the commencement of your paper (p. 194), justice also requires of me to state, that I have not been in the slightest degree instrumental in the improvement of any part of the apparatus of the said carriage; but that whatever merits it may possess, in the present arrangement of its parts, will be found in the specification of the original patents granted to Mr. W. H. James, in the years 1824 and 1825.

In your comments upon my account of the carriage given in the " Register," you treat with ridicule the assertion that I could manage to carry one of the engines in each of my coat-pockets; and you say that I ought to have added,

all but-the furnace, flue, chimney, boiler," &c. Now, Sir, this is just as reasonable, as to require of you, because you may have undertaken to carry a hackney-coach, to carry a horse also, under each arm, with all the harness, &c. In this case the coach is the machine, and the horses the power, just the same as in the other case of the

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engine and the boiler. But if we admit your argument to be correct, you ought to be loaded with eight horses; since the boiler in Messrs. Anderson and James's carriage, which you are desirous of burdening me with, supplies the power to four engines.*

The hurdy-gurdy process," as you facetiously term an early proposition of Mr. James's, for cleaning out the annular chambers of his boilers, I can inform you, is not practised at all; nevertheless it is a very effectual one, and is employed at Birmingham for scouring and brightening various me tallic articles. A more convenient and rapidly executed process is now adopted in lieu, which prevents the lodgement of any sediment whatever, and requires only the attention of the engine-man for a few seconds every day; and if neglected for a long period, so as to allow the formation of a hard encrustation, it is removed by a similar process, almost instantaneously, without labour, and without the employment of any chemical agent. For the present, I believe, it is not intended to make the process public.

In my remarks upon the velocities attainable by the carriage of Messrs. Anderson and James, you seem to consider that I have contradicted myself, and request an explanation, which I take pleasure in affording. In saying that arrangements had been made for increasing the speed beyond 12 miles an hour, I had reference to the application of "fast-gear." The "slow-gear" having been proved adequate to propel the carriage at the rate of twelve miles an hour, and the "fast-gear" being adapted to communicate 34 times the speed of the slow to the running wheels, it was quite correct to state that "arrangements had been made to increase the speed to twenty or more miles," although it was not deemed advisable to use it" on the thronged public roads."

With respect to a blast, I think, Sir, you will find that I have not said it was "both necessary and unnecessary," but the latter only.-That although great effects might be produced by it, it was inexpedient, on account of its pernicious effects upon the metal of the boilers.

You express a doubt of the constant effect of the boilers on the plan of those in question, which may at once be removed by your visiting+ Messrs. Ander

We miss the analogy entirely-if there is any-and must refer the reader again to what we have said on the subject.-ED. M. M.

We shall take an early opportunity of doing so, and shall report the result to our readers. ED. M. M.

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son and James's manufactory, at Vauxhall; where, I make no doubt, the proprietors will take pleasure in showing you their engine, which has been constantly at work, twelve hours per day, ever since the manufactory was established. They have also recently started a small steam-boat, propelled by machinery and boilers on the same principle, in which I recently made a voyage to Richmond and back (27 miles altogether), in 4 hours and 5 minutes; 19 miles of which was against the current. This is quite as fast as any of the Richmond boats, if not faster; and it was performed under the unfavourable circumstance of the paddles being much too deep in the water; and when you are informed that the radius of the wheel was then less than three feet, you will readily conceive how disadvantageously the paddles must have worked. The boat is unquestionably the safest on the river; and when her paddles are altered, so as to waste less of the power, I confidently anticipate she will be also the quickest.

I remain, Sir, respectfully,
Your obedient servant,
L. HEBERT.

20, Paternoster-row,
Nov. 21, 1829.

BRAITHWAITE AND ERICSSON'S BOILER.

Sir, Mr. Braithwaite's last letter, although elegantly written, contains so little substance of a tangible nature, that a very brief reply to it will suffice.

I am accused therein of disingenuousness, for admitting (as he states) that it was the flue of the furnace which gave way, and not the boiler. Now, as Mr. Braithwaite has over and over again insisted that that was the true nature of the occurrence, he ought to have charged me with ingenuousness for admitting it. It being however recorded in your pages that so far from admitting any such thing, I re-asserted (and in my own judgment proved clearly) the contrary: to whom, I would ask, in the name of common sense, does the charge of disingenuousness apply?

I remain, Sir, respectfully,
Your obedient servant,
L. HEBERT.

20, Paternoster-row,

Nov. 23, 1829.

Sir, Had Mr. Hebert himself treated the question of the merits of Messrs. Braithwaite and Ericsson's boiler "scientifically," as he wishes me to do, I should never have interfered in the matter. I am no man of science, only a friend to truth and fair play; in which character, and no other, I have presumed to use a byestander's privilege. Mr. Hebert says the question is "simply one of science.' I submit, that it is simply and exclusively one of fact. The Editor of the "Register of Arts" has asserted and re-asserted, that the yielding of the furnace-flue of "The Novelty" was owing to the application of a blast to the furnace; the Editor of the "Mechanics' Magazine" has certified, that the real cause was the want of a sufficient supply of water to keep that flue covered. The question then shortly is, which are we to believe? Mr. Hebert, who was not present at the late competition, who has never seen the engine in question, and who can, for both these reasons, know personally nothing of the matter? Or Mr. Robertson, who was on the spot at the time of the accident, who personally investigated the cause of it, and who has stated nothing concerning it but as of his own knowledge? We want no lights from science to enable us to determine on which side the truth in this case lies. A very small share of common penetration is all that is requisite to lead every one to the same conclusion. Neither do we want any help from science to unmask the purpose which is to be served by Mr. Hebert's invented version of the affair. By persisting in the assertion that the blast was the cause of the accident, Mr. Hebert wishes to make it appear that the principle of the engine was in fault: while, by frankly recognising that the want of water was the cause, he would be forced to acknowledge that the accident was one of the most ordinary description (such as his friend" Betty" must have often en

countered in the course of her culinary practice); and one which did not at all affect the principle of the engine, since it would have been equally sure to happen, whether a

[In a private letter with which we have been favoured from a respectable engineer, the operation of a blast when applied to a steam-engine furnace is so much better explained than it has been yet done by any of the parties to this rather protracted dispute, that though the letter was not intended for publication, we must take leave to quote so much of it as bears on the point in hand. It will, we hope, serve to convince Mr. Hebert, that the reason as well as the truth of the case is on the side of his opponents:-" We usually associate (says the writer) with the word blast the idea of a sudden and impetuous gust, operating at intervals, directed to and impinging on some one point: a blast of which description would of course soon destroy the strongest metal subjected to its influence. But this is a term wholly inapplicable to the case of feeding the close fire of a steam-boiler with air: for many times the quantity of air that would pass through a fire by a common draught, may be delivered as softly and regularly by means of a forcing apparatus, and without the least determination towards any one point of the furnace or flue, as if no such apparatus were employed. It is altogether absurd, and contrary to every-day experience, to pretend there can be any danger to apprehend, from any addition which a pair of bellows such as those of The Novelty' can make to the volume of air passed through a furnace."-EDIT.]

THE ALMANACS FOR 1830.

(Continued from p. 218.) THE ENGLISHMAN appears to us to be for every body's use the best of all the

We stated last week that this al

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almanacs published. Not only does it give a great deal more information in the same space, and for the same money, than any other; but that information is uniformly of a more select, accurate, and generally useful description. We find in it most of what is valuable in the old almanacs, without any of those faults which have been made such grievous matter of charge against them; and much, very much, of the highest value, that is quite new, and to be met with no more else. While "The Englishman" is as free from every taint of "superstition, prejudice, and indecency," as "The British" itself, it is, by we know not how many degrees, more learned and instructive. We have not here to lament repetitions on repetitions, or to wonder at blank spaces devoted to the "diffusion" of waste paper; every corner almost is filled with information at once new and useful. The whole, too, is printed in so beautifully distinct and clear a manner, though with types of every variety of minuteness, as to be legible with the greatest ease.

The Calendar pages of "The Englishman" exhibit this year an improvement alike remarkable for its novelty and importance. Instead of merely exhibiting the moon's risings for every day from the full moon to the new, and the moon's settings for every day from the new moon to the full, there is now given, for the first time in any English Almanac, the time of the moon's rising and setting for every day in the year.

In order to make room for the two columns containing this new information, an abbreviation of comparatively little consequence has been made in the Tide Table. The time of the primary high-water, or that which depends upon the moon's coming to the south, is all that is given; while the secondary highwater, or that which depends upon the moon's being on the opposite part of the meridian, is omitted. It is stated, that "the time of the secondary high-water may always be found with sufficient accuracy, by taking the midway between any day's high-water and that of the following day."

manac owed its existence entirely to the rivalry of The British ;' but we have been since assured, on the best authority, that "The Englishman' was planned before 'The British' was heard of, and would have appeared last year, although The British' had never existed.'