This scheme also proved abortive, and for forty years more the travelling public put up with what they could get, but at last in 1860 the North British Railway fixed upon a site about six miles to the west of South Queensferry as suitable for the construction of a railway bridge. The bridge was to have consisted of a number of large spans of 500 ft. each in the centre, with approaches in shorter spans at either end. The exact centre line was to have been from a point near Blackness Castle on the south shore to Charleston on the north shore, and connecting lines from near Linlithgow, on the Edinburgh and Glasgow line on the one side, and from Charleston to Dunfermline on the other side, would no doubt have established a very good through line to the north. Borings were taken and other investigations made. A design had been drawn out by Sir Thomas (then Mr.) Bouch, and Parliamentary powers for the construction of the bridge were obtained by an Act in 1865. The river here is about 2½ miles wide, and the greatest depth of water about 60 ft.—but the bottom is loose and uncertain, and it was decided to build up and sink an experimental pier before proceeding further. But troubles intervened, and during the re-arrangement of the North British Railway Company in 1866-1867, the project was abandoned through various causes. For it were substituted improvements in the Queensferry passage by the construction of the railway slips at North Queensferry and Port Edgar. It was at first intended to have swinging landing-stages at each end, rising and falling with the tide—the trains by means of these to be run on and off the ferry steamers. The latter portion of the scheme was not carried out however, owing to the insufficient depth of water and the gradual silting up near the piers, which necessitates the periodical assistance of dredgers to keep a channel clear, although the ferry steamer draws little more than 4½ ft. of water. These conditions are a source of much discomfort to the passengers by this route for the light draught steamer can hardly hold its own against a gale of wind broadside on, and many people become seasick during a passage lasting at the worst of times barely twenty minutes.
In 1873 the Forth Bridge Company was formed for the purpose of carrying out the design by Sir Thomas Bouch of a suspension bridge with two large spans of 1600 ft. each. The capital was raised by the four principal railway companies interested in the East Coast traffic—namely, the Great Northern, the North-Eastern, the Midland, and the North-British, and the companies came to an understanding among themselves that they would between them send so much traffic across the bridge as would suffice to pay a dividend of 6 per cent. per annum on the contract sum. The Act authorising the construction of the bridge was passed in the same year, 1873, and a contract signed, with Messrs. W. Arrol and Co., of Glasgow. An illustration showing elevation and plan of Sir Thomas Bouch's design is shown in Fig. 2. The central towers from which the main chains are suspended were to have been 550 ft. above high water, while the rail level would be at such height as to leave a clear head-room of 150 ft. above high water between the piers. The central tower on Inchgarvie was over 500 ft. long, which brought the foundations upon the sloping rock down to a depth of over 110 ft. below high water. There were two lines of rails carried at a distance of 100 ft. from each other, each line being supported on a pair of strong lattice girders, and these were laterally stiffened by single diagonal bracings reaching from side to side. The piers at Queensferry and on Fife were very nearly in the same position as those of the present bridge, and there were two approach viaducts to reach the high ground upon either side. The bridge was to have been constructed entirely of steel.
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Offices and workshops—which are now standing—were built at Queensferry, and extensive brickworks near Inverkeithing laid out and started. A brick pier—one of eight, which were to form the base of the great Inchgarvie tower—was built at the extreme north-west corner, after a foundation stone had been laid with great ceremony. But the collapse of the ill-fated Tay Bridge in December, 1879, stopped the further progress of the work, and the investigations into the causes of that disaster, and the disclosures made, shook the public confidence in Sir Thomas Bouch's design, and rendered a thorough reconsideration of the whole subject necessary. As a first result of this, the suspension bridge was abandoned, and the four railway companies above named instructed their consulting engineers—Messrs. Barlow, Harrison, and Fowler—to meet and consider the feasibility of building a bridge for railway purposes across the Forth, and assuming the feasibility to be proved, to decide what description of bridge it would be most desirable to adopt. It was fairly well known how many types of bridge there were to select from for such a site; these were (1): Mr. Bouch's original design (Fig. 2); (2) three forms of suspension bridges with stiffening guides and braced chains (Fig. 3); and (3) a cantilever bridge (Fig. 4). The inquiry was most comprehensive. It embraced not only bridges as set forth, but also tunnels, and both of these for different sites.
With regard to tunnels, it was considered that
