24 The Tay Bridge. 



on the upper member of the girders, but for a distance of 

 3149 feet in the centre of the stream the sunk platform 

 type of bridge is adopted, the traffic passing between the 

 girders, which are braced together overhead so as to form a 

 lattice tube or cage. This is intended to secure head-way 

 for navigation. 



This portion is perfectly straight, and contains all the 

 larger openings, the length being composed of 11 spans of 

 245 feet each, and 2 of 227 feet. 



The height of the bridge above the water varies con- 

 siderably, the greatest altitude being attained in the portion 

 last described, where the soffit of the girders appears to have 

 been about 90 feet above high- water mark. 



To give a clearer idea of the magnitude of the structure, 

 we may state that the total length would reach from the 

 gate of the University grounds, in Grattan-street, to the 

 barracks on the St. Kilda-road, while the " high girders," or 

 sunk platform part, would correspond to the distance from 

 the Public Library to Prince's Bridge, and the total height 

 above high- water mark to that of the top of the flagstaff at 

 the General Post Office above the pavement in Elizabeth- 

 street. 



On Sunday evening, 28th December, 1879, a train left the 

 southern end of the bridge for Dundee. The night was 

 cloudy, and a heavy gale was blowing from the westward. 

 The lights of the train were watched until the high girders 

 were reached, when they disappeared, and the moon shining 

 out shortly after, revealed the appalling fact that the whole 

 of the larger spans had fallen, and with them the train. A 

 closer examination showed that the foundations of the piers, 

 which were constructed of brickwork up to a height of 

 about 5 feet above high-water mark, remained intact, while 

 the upper portions, consisting, as before mentioned, of cast- 

 iron columns, were almost entirely destroyed, and the cage, 

 3149 feet long, formed by the girders, cross-girders, and hori- 

 zontal bracing, lay bruised and twisted, but still recognisable, 

 with the train inside it, about 20 yards to the leeward of the 

 brick foundations. 



Detailed views of the wreck and other particulars are to 

 be found in the Engineer of January 2nd, 9th, 30th of the 

 present year, and Engineering of the same dates. As soon 

 as the particulars of the disaster became generally known, 

 various theories were proposed to account for it, the 

 principal of which we shall now proceed to consider. 



