430 THE BRITANNIA BRIDGE. CHAP. XIX. 



on from morning till night. In fitting the Britannia 

 tubes together, not less than 2,000,000 of bolts were 

 riveted, weighing some 900 tons. 



The Britannia Bridge consists of two independent 

 continuous tubular beams, each 1511 feet in length, and 

 each weighing 4680 tons, independent of the cast-iron 

 frames inserted at their bearings on the masonry of the 

 towers. These immense beams are supported at five 

 places, namely, on the abutments and on three towers, 

 the central of which is known as the Great Britannia 

 Tower, 230 feet high, built on a rock in the middle of the 

 Strait. The side towers are 18 feet less in height than 

 the central one, and the abutments 35 feet lower than 

 the side towers. The design of the masonry is such as 

 to accord with the form of the tubes, being somewhat 

 of an Egyptian character, massive and gigantic rather 

 than beautiful, but bearing the unmistakable impress of 

 power. 



The bridge has four spans, two of 460 feet over the 

 water, and two of 230 feet over the land. The weight 

 of the longer spans, at the points where the tubes repose 

 on the masonry, is not less than 1587 tons. On the 

 centre tower the tubes lie solid ; but on the land towers 

 and abutments they lie on roller-beds, so as to allow of 

 expansion and contraction. The road within each tube 

 is 15 feet wide, and the height varies from 23 feet at 

 the ends to 30 feet at the centre. To give an idea of 

 the vast size of the tubes by comparison with other 

 structures, it may be mentioned that each length con- 

 stituting the main spans is twice as long as London 

 Monument is high ; and if it could be set on end in 

 St. Paul's Churchyard, it would reach nearly 100 feet 

 above the cross. 



The Conway Bridge is, in most respects, similar to 

 the Britannia, consisting of two tubes, of 400 feet span, 

 placed side by side, each weighing 1180 tons. The 

 principle adopted in the construction of the tubes, and 



