in consequence, Mr. Brunel went to work in a somewhat bolder way than he had otherwise intended. The soil was the great object of deliberation, for upon it depended at what level the Tunnel should be commenced. The assistance of some eminent geologists was here of great moment. These informed the engineer that below a certain depth the soil would be a kind of quicksand, and therefore advised him to keep above it, and as close as possible to the stratum of clay forming the bed of the river. We shall presently see that the geologists were right.

We are not about to give a technical description of the progress of the works of the Tunnel, which could be interesting alone to the professional or scientific man; but we must notice at some length two or three of their chief points, not only because the success of the work has depended upon them, but because in their admirable simplicity, as well as their wonderful fitness to the purposes designed, they cannot fail to be universally understood and appreciated.

And first of the construction of the shaft with which the Tunnel was commenced in March, 1825. This seems to our eyes, uninitiated in the wonders of engineering, not one of the least marvels of this altogether marvellous work. A space being marked out a hundred and fifty feet distant from the river, the bricklayers began raising a round frame, or cylinder, three feet thick and one hundred and fifty feet in circumference. This was strengthened in various ways, by iron rods, &c., passing up the centre of the thickness; and was continued to the height of forty-two feet. The excavators now commenced their work on the inside, cutting away the ground, which was raised to the top of the shaft by a steam-engine there placed, and which also relieved them from the water that occasionally impeded their descent. We may imagine the wonder with which a person unacquainted with the object of these preparations must have beheld that enormous mass of masonry at last beginning to descend regularly and peacefully after the busy pigmies who were carving the way for it, and at the same time, as it were, accommodating itself to the convenience of the bricklayers, who, in order to give it the additional height required, had merely to keep adding to the top as it descended. This is the history of the great circular opening into which the visitor passes from the little lobby, and where he beholds, in the centre, an elaborate machinery of pumps, connected with a steam-engine, raising its four hundred gallons per minute, and, as though that was really too trifling for an engine of its respectability of power, performing into the bargain the duties of drawing carriages along the railway, which as yet occupies one of the two arches of the Tunnel, and that of hoisting and letting down all the heavier articles passing between the upper and lower world. We must not omit to observe, with regard to the shaft, that by its means the bed of gravel and sand twenty-six feet deep, full of land-water, in which the drift-makers of the earlier attempt had been compelled to narrow the dimensions of their already small shaft, was passed without inconvenience. We may add also that, when the shaft was sunk to its present depth of sixty-five feet, another shaft, of twenty-five feet diameter, was sunk still lower, till, at the depth of eighty feet, the ground suddenly gave way, sinking several feet, whilst sand and water were blown up with some violence. This confirmed the statement of the geologists, and satisfied the engineer as to the propriety of the level he had chosen.

The shaft accomplished, the Tunnel itself was begun at the depth of sixtythree feet. The excavation Mr. Brunel proposed to make from bank to bank was to be about thirty-eight feet broad and twenty-two and a half high, which, being defended by strong walls, was to leave room within for a double archway, each fifteen feet high, and wide enough for a single carriage-way and a footpath. The mode in which this great excavation was accomplished has been the wonder and admiration of the most experienced engineers, and will for ever remain a monument of the genius of its author. The engravings before us represent two

views of the working of the shield, by means of which the weight of the superincumbent bottom of the river has been supported, whilst the men who were undermining it were sheltered in its little cells below. This mighty instrument-one in idea and object, but consisting of twelve separate parts or divisions, each containing three cells, one above the other-is thus used. We will suppose that, the work being finished in its rear, an advance is desired, and that the divisions are in their usual position-the alternate ones a little before the others. These last have now to be moved. The men in their cells pull down the top poling-board, one of those small defences with which the entire front of the shield is covered, and immediately cut away the ground for about six inches. That done, the poling-board is replaced, and the one below removed, and so on till the entire space in front of these divisions has been excavated to the depth of six inches. Each of the divisions is now advanced by the application of two screws-one at its head, and one at its foot—which, resting against the finished brickwork, and turned, impel it forward into the vacant space. The other set of divisions then advance. As the miners are at work at one end of the cells, so the bricklayers are no less actively employed at the other, forming the brick walls of the top, sides, and bottomthe superincumbent earth of the top being still held up by the shield till the bricklayers have finished. This is but a rude description of an engine almost as remarkable for its elaborate organization as for its vast strength. Beneath those great iron ribs a kind of mechanical soul really seems to have been created. It has its shoes and its legs, and uses them too with good effect. It raises and depresses its head at pleasure; it presents invincible buttresses in its front to whatever danger may there threaten, and, when the danger is past, again opens its breast for the further advances of the indefatigable host. In a word, to the shield the successful formation of the Tunnel is entirely owing. We may add that following the shield was a stage in each archway for the assistance of the men in the upper cells.

But, great as was the confidence of Mr. Brunel in his shield, and the resources which he must have felt he had within himself, ready for every difficulty, it is impossible that he could have ever anticipated the all but overwhelming amount of obstacles that he has actually experienced, principally from the character of the soil, and the extraordinary influence which the tides exercised even at the Tunnel's depth. The first nine feet of the Tunnel (commenced with the new year, 1826) were passed through firm clay; then came a loose watery sand, where every movement was made with imminent hazard. Thirty-two anxious days passed in this part. Substantial ground again reached about the 14th of March, matters went on prosperously till September following, by which time two hundred and sixty feet had been completed. On the 14th of that month the engineer startled the Directors with the information that he expected the bottom of the river, just beyond the shield, would break down with the coming tide. It appears he had discovered a cavity above the top of the shield. Exactly at high tide the miners heard the uproar of the falling soil upon the head of their good shield, and saw bursts of water follow; but so complete were the precautions taken that no injury ensued, and the cavity was soon filled by the river itself. Another month, and a similar occurrence took place. By the 2nd of January, 1827, three hundred and fifty feet were accomplished, when the tide, during the removal of one of the poling-boards,

forced through the shield a quantity of loose clay; but still no irruption of the river itself followed-the fear of which, from the commencement to the termination of the work, was continually upon every one's mind. From January to April the Tunnel proceeded at an excellent rate, although the ground continued so very moist that, in the latter month, an inspection, by means of a diving-bell, of the bed of the river became necessary. Some depressions were observed, and filled up by the usual means-bags of clay. A shovel and hammer, being accidentally left on this occasion in the river, were afterwards found during an influx of loose ground through the shield, having descended some eighteen feet. This little circumstance shows the nature of the ground above, and the all but invincible difficulties through which the engineer had to make his way. But the more important incidents of the work-those which were to put his ability and fortitude to the severest tests-were now coming on. About the middle of May, some vessels, coming in at a late tide, moored just over the head of the Tunnel. The consequence was, that the obstruction they presented to the water caused a great washing away of the soil beneath. What followed may be best described in the words of Mr. Beamish, the then resident assistant-engineer, with whose Report of this, the first irruption of the river, we have been favoured among other interesting matter, and which we give as a perfectly dramatic view of the scene, the actors, and the event.

"May 18, 1827. Some of the faces cut down without difficulty. As the water rose with the tide, it increased in the frames very considerably between Nos. 5 and 6, forcing its way at the front, then the back: Ball and Compton (the occupants) most active. About a quarter before six o'clock No. 11 (division) went forward. Clay appeared at the back. Had it closed up immediately. While this was going forward my attention was again drawn to No. 6, where I found gravel forcing itself with the water. It was with the utmost difficulty that Ball could keep anything against the opening. Fearing that the pumpers would now become alarmed, as they had been once or twice before, and leave their post, I went upon the east stage to encourage them, and to chase more shoring for Ball. Goodwin, who was engaged at No. 11, where indications of a run appeared, called to Rogers, who was in the act of working down No. 9, to come to his assistance. But Rogers, having his second poling (board) down, could not. Goodwin again called. I then said to Rogers, 'Don't you hear?' Upon which he left his poling for the purpose of assisting Goodwin; but before he could get to him, and before I could get fairly into the frames, there poured such an overwhelming volume of water and sludge as to force them out of the frames. William Carps, a bricklayer, who had gone to Goodwin's assistance, was knocked down, and literally rolled out of the frames on the stage as though he had come through a mill-sluice; and would undoubtedly have fallen off the stage had I not caught hold of him, and with Rogers's assistance helped him down the ladder. I again made an attempt to get into the frames, calling upon the miners to follow; but all was dark (the lights at the frames and stage being all blown out), and I was only answered by the hoarse and angry sounds of Father Thames's roarings. Rogers (an old sergeant of the Guards), the only man left upon the stage, now caught my arm, and, gently drawing me from the frames, said, 'Come away, pray sir, come away; 'tis no use, the water is rising fast.' I turned once more; but,

hearing an increased rush at No. 6, and finding the column of water at Nos.11 and 12 to be augmenting, I reluctantly descended. The cement-casks, compo-boxes, pieces of timber, were floating around me. I turned into the west arch, where the enemy had not yet advanced so rapidly, and again looked towards the frames, lest some one might have been overtaken; but the cement-casks, &c., striking my legs, threatened seriously to obstruct my retreat, and it was with some difficulty that I reached the visitors' bar,* where Mayo, Bertram, and others, were anxiously waiting to receive me. I was glad of their assistance; indeed, Mayo fairly dragged me over it. Not bearing the idea of so precipitate a retreat, I turned once more; but vain was the hope! The wave rolled onward and onward. The men retreated, and I followed. Met Gravatt coming down. Short was the question, and brief was the answer. As we approached I met I. Brunel. We turned round: the effect was splendid beyond description. The water as it rose became more and more vivid, from the reflected lights of the gas.

As we reached the staircase a crash was heard, and then a rush of air at once extinguished all the lights. . Now it was that I experienced something like dread. I looked up the shaft and saw both stairs crowded; I looked below, and beheld the overwhelming wave appearing to move with accumulated velocity. Dreading the effect of the reaction of this wave from the back of the shaft upon our staircase, I exclaimed to Mr. Gravatt, The staircase will blow up!' I. Brunel ordered the men to get up with all expedition; and our feet were scarcely off the bottom stairs, when the first flight, which we had just left, was swept away. Upon our reaching the top, a bustling noise assailed our ears, some calling for a raft, others a boat, and others again a rope; from which it was evident that some unfortunate individual was in the water. I. Brunel instantly, with that presence of mind to which I have been more than once witness, slid down one of the iron ties, and after him Mr. Gravatt, each making a rope fast to old Tillet's waist, who, having been looking after the packing of the pumps below the shaft, was overtaken by the flood. He was soon placed out of danger. The roll was immediately called-not one absent!"

The diving-bell being again employed, and the hole or chasm discovered, some three thousand bags of clay, armed with small hazel rods, were expended before it was effectually closed. On the 21st of the next month the water in the Tunnel was got under; but it was not till the middle of August that the soil' forced in was completely cleared away, and the engineer able to examine the effect of the irruption on his work. The structure was found perfectly sound, even whilst a part of the brick-work close to the shield was reduced to nearly half its original thickness by the tremendous violence of the rushing waters, whilst the chain which held the divisions of the shield together had been snapped like a twig, and whilst various heavy pieces of iron belonging to the shield were found driven into the ground as if by a battering-ram. Progress was now recommenced; and here we would pause a moment to pay a just tribute of admiration to the men, as well as to their directors, for the courage they have so constantly evinced. Even now, as they resumed their labours with the impression of the recent event fresh upon their minds, something or other was constantly occurring to excite fresh alarm. Now a report would take place in the frames like a cannon-shot, some part having * A bar so placed as to keep the visitors at some little distance from the shield and the unfinished works.