considering the difficulties of the execution, one of the most perfect works of its class. In extent, and in some respects for cleverness of execution, even this bridge is surpassed by that across the St. Lawrence at Montreal, which, though only a single tube, is 6592 feet long, but the centre span is only 330 feet, and the remaining 24 openings average 242 feet. The great engineering difficulty was the erection of such a structure on so rapid a river, frozen at times, and at the breaking up of the ice bringing down great bergs which threaten to overwhelm everything. All these difficulties have been successfully surmounted, and the bridge promises to be as stable as it is efficient.

Neither of these, however, has reached the limits of the system. When, for instance, it was proposed to erect a railway bridge across the Rhine at Cologne, Mr. Fairbairn gave two designs: one for a bridge in four spans, which it was estimated would cost when complete 2301. per foot, and one in two spans, the expense of which would have been 2807. The latter would have consisted of two tubes, carrying the railway with the roadway between them and footways outside, each tube measuring 1140 feet, supported by one pier in the centre; the two spans being thus 100 feet in excess of those of the Menai Bridge. Indeed there seems no reason why openings of 700 or 800 feet might not be bridged by these means. Whether or not this is the cheapest mode of accomplishing the object is not quite clear. The Menai, with its double road, cost 4007. per foot; and the Montreal, with its single line, 1717. But the only economy that could be made is in the vertical web that connects the top and bottom. All engineers are pretty well agreed as to the amount of metal which is required to provide a given amount of strength to the top and bottom for a given span, but they differ as to the mode of forming the sides. Thus the great tubes of the Menai Bridge weigh about 1600 tons; 500 tons of this weight is in the top, and a like quantity in the bottom, and consequently 600 in the sides.* Half that quantity would suffice according to some, and con

*The smaller Montreal tubes weigh 252 tons, made up thus :

So the only economy could be effected in the last item, and this is very inconsiderable compared with the whole cost. For according to the published account the masonry of the piers cost 1147. per foot of the bridge, leaving only 571. for the iron work, and the only saving that could be effected would be on one-third of this. Vol. 114.-No. 228.

Y

sequently

sequently all conceivable forms of lattice girders and trusses have been employed for this purpose, and have economised metal to a great extent; but it has yet to be ascertained whether they are as stable. There is a grand simplicity in a wall of iron, every inch of which is as available in tension as it is in compression, and consequently can take all the, varying strains of the traffic without suffering from the inequality; whereas the best designed truss must always be stronger and better in one position than another, and depends more or less on bolts and fastenings, which any inequality or sinking may throw out of work. If such be the case, it is to be regretted, for it is to be feared that the tubular girder can never be other than ugly; while many of those composed of diagonal framings are pleasing in themselves. A mere lattice like that at Cologne is not better than a tube, and is as flimsy as it looks; but a welldesigned truss like that of the Charing-cross Bridge is a beautiful thing in itself, and, if the bridge really cost only 1307. per foot for four lines of rails, is as cheap an expedient as can well be adopted. The spans, however, are only 154 feet, which, of course, prevents its being compared with the great works just

mentioned.*

In the early ages of engineering experience, tunnels seemed far more formidable undertakings than bridges. Men could face what they saw, and undertake what they could calculate; but it was another thing to burrow into the bowels of the earth to encounter rocks or quicksands, or it might be springs and moving clays, and all this in darkness, and in ignorance of what might come next. All these things are now become perfectly understood, and the mode of making them settled. There have, in fact, been more than eighty miles of tunnels excavated for railways in this kingdom alone under every variety of circumstances and difficulty, and at an average cost of only 157. per foot forward. The experience so gained has been such that were it now proposed to execute a new tunnel under the Thames, there are twenty contractors who would be ready to undertake it, and could carry it through. The first, indeed, would hardly have been found so difficult of execution, had it not been carried too near the bottom of the river, where the soil was only recent sediment and rubbish.

We have become so familiar with these wonders that it is

*For the railway bridge now erecting between Southwark and London bridges Mr. Hawkshaw proposed, in order not to interfere with the traffic, to make the central arch 300 feet span,-which would have been a really grand object,―the side arches 150. The authorities decided that if there was one arch larger than the others all the traffic would go through it, and consequently ordered them all to be made equal, so that the bargees might be puzzled which to choose!

curious

*

curious to look back on the interest and excitement caused by an attempt to carry a roadway under the Thames, and still more to turn to what occurred less than one hundred years ago (in 1766), and mark the incredulity and the ridicule which were displayed when Brindley proposed to cut the Harecastle Tunnel in Staffordshire. Yet this was only nine feet wide by twelve feet high, and 2880 yards long; and as the highest summit of the hill through which it was cut is only 190 feet above the tunnel, it could be and was worked by means of fifteen shafts from above. Even this tunnel took eleven years to execute, and at times its daring projector almost despaired of success, nor did he live to see it completed. Compare this with the great tunnel under Mount Cenis, nearly five times its length, and at a depth of an English mile (1600 metres) below the summit, so that shafts being impossible it has to be worked wholly from the ends, and so far as can be ascertained through hard rock the whole way; yet there is no reason to suppose that it will take longer than Brindley's tunnel to execute. But the remarkable fact is that no one seems to doubt the success of the undertaking, and any one attempting to ridicule its projectors would only render himself ridiculous. Yet though none doubt the practicability, many doubt the expediency of the undertaking; the truth being that since it was commenced railway engineering has made such progress, it is by no means clear that it would not have been better to keep on the surface of the earth and climb the pass, steep though it might be, than to excavate a tunnel so unavoidably expensive as this one must prove.

It may appear a strange assertion, but it is nevertheless true, that timidity is the cause which has hitherto most retarded the progress of railways. Men hesitated long in employing them, because they were afraid that the smooth wheels would not have sufficient hold on the smooth rails to enable them to draw. They were afraid to join their rails for fear the expansion would cause them to rise and twist; but the most curious thing is that long after the introduction of the present system they were afraid the locomotive could not climb gradients so steep as 1 in 100. The consequence was that ropes with stationary engines were employed-engineers wasted their time and their shareholders' money in inventing atmospheric traction and fifty other devices to get over this difficulty. At last they tried-and now any one may see the locomotive coming from Oldham to Manchester, dragging very heavy trains up an incline of 1 in 27, which is about the slope of Ludgate Hill;

*The tunnel is to be as nearly as may be 40,000 feet long, and is estimated to cost 501. per foot forwards, or two millions sterling. Y 2

and

and in America, in some of the mountain passes of Virginia, they rise 1 in 17 and 1 in 20, the latter being the slope of Holborn Hill, which tasks our local traffic so severely; more even than this, it is asserted that the locomotive has actually scaled an incline of 1 in 10 with a load greater than its own weight.* This is probably a steeper slope than any turnpike road we have, Whether it is an expedient or economical mode of employing engines to use them in dragging loads up such steep slopes is another question, not so easily answered; † but it proves that the capabilities of the railway system for extension are unlimited. For though on all main lines where the traffic is great and the trains heavy and frequent, no expense should be spared to obtain easy gradients, still on branch and local lines, where loads are light and trains few, any gradient that will do for carriage traffic will do for the rail. It is also found that where the country undulates and the inclines are not long, there is really no great expenditure of power in working them, the ease with which the downward slope is descended going far to compensate for the exertion required in ascending. It is when the slope is long and continuous that the powers of the engine are most severely tasked; yet even in that case, great things may be accomplished.

One of the first great lines on which this discovery was utilized was the line over the Semmering pass in the Noric Alps on the line joining Vienna and Trieste. The ascent on the north side is 134 miles long, in the course of which 1325 feet are ascended on an average of 1 in 47, and in one place the gradient is 1 in 40, and in addition to this the curves are so sharp and the construction of so expensive a nature that to work it and keep it in repair absorbs the whole profits of the line. The descent on the other side to Murzuschlag is on the back of the slope, nearly straight, and with a uniform gradient of 1 in 50 is worked with facility and without great additional expense.

The Bhore Ghât incline, which has just been completed on the line from Bombay to Central India, is a more formidable and more extraordinary piece of engineering than even this. It is 15 miles in length, and the height surmounted is 1831 feet, so that the average is 1 in 48, or about the same as the Semmering; but for one mile and a half it is 1 in 37, and for 8 miles 1 in 40. The amount of tunneling, bridging, and embanking on the Indian line is such that the cost was

*Minutes of Proceedings of Institute of Civil Engineers,' vol. xviii. p. 51. At 36 miles per hour the resistance in rising 1 foot in 100 is doubled thus:Resistance in dead level 224 lbs. to ton of load.

39

1 in 100

448 lbs.

or, in other words, an engine that can drag 200 tons at a certain speed on a level, can only draw 100 tons at 1 in 100, and so on in proportion.

1,100,000l.,

as may

1,100,000l., or upwards of 68,000l. per mile, which is as near be the cost of the other. This railway has one advantage over its Alpine competitor-that all the heavy traffic is down the incline, and the trains may go up the Ghât either empty or only partially laden, whereas on the Austrian line the heavy traffic is towards the port and up the incline.

As before mentioned, the Americans work some inclines with a steeper gradient than even these, but never so long or of so permanent a character. But it is now proposed to cross the Simplon by a railway, and before long Innspruck will be connected with Verona-so that it can hardly be said that any mountain chain which has been traversed by roads is inaccessible to the steam horse. Even the Himalayas might be so traversed; and if a hundred years hence some unborn Brunel be called upon to make designs for the Lahore and Ladak Junction Railway, and find himself forced to tunnel through the ridge-it will not be that the engine could not climb a pass even 18,000 feet above the level of the sea, but that the perennial snows of those regions would form so unsuitable and so unsatisfactory a foundation for his permanent way.

No very recent statistics have been published which would enable us to state precisely what number of miles of railway are made or making, or what they have cost, but it is certainly no exaggeration to say that a sum larger than our National Debt has been spent on these undertakings in the Old World during the last thirty years; and there is no reason to suppose that that sum will not be doubled during the next thirty, if peace continues and commercial prosperity advances with the same rapid strides that it has been taking latterly. Already almost every capital in Europe is united directly or indirectly with every other, except Constantinople; and even the stolid indifference of the Turk cannot long save 'old Stamboul's walls' from being profaned by the scream of the railway whistle.

When Russia has completed the junction of the Baltic with the Black Sea and the Caspian, which she is now engaged upon, there will remain two great enterprises which the next few years will probably see undertaken, if not accomplished. As soon as the Americans are tired of fighting, they will set about connecting the Pacific with the Mississippi; and, notwithstanding the immense tracts of prairie that separate the two, they will no doubt accomplish it. The task of the Old World is to join the Indian lines with those of Europe. Political difficulties and the ignorant bigotry of the three great Mahomedan states of Afghanistan, Persia, and Turkey may retard this; but whether it is done through Turkey or Russia, there are no engineering difficulties that could not be