432 FLOATING THE CON WAY TUBES. CHAP. XIX. 



history of the construction of the Britannia and Conway 

 Bridges we would refer the reader for full details 

 as to the methods of construction employed in these 

 extraordinary works. 



The floating of the tubes on pontoons, from the places 

 where they had been constructed to the recesses in the 

 masonry of the towers, up which they were to be hoisted 

 to the positions they were permanently to occupy, was 

 an anxious and exciting operation. The first part of this 

 process was performed at Conway, where Mr. Stephen- 

 son directed it in person, assisted by Captain Claxton, 

 Mr. Brunei, and other engineering friends. On the 6th 

 March, 1848, the pontoons bearing the first great tube 

 of the up-line were floated round quietly and majesti- 

 cally into their place between the towers in about twenty 

 minutes. Unfortunately, one of the sets of pontoons 

 had become slightly slued by the stream, by which the 

 Conway end of the tube was prevented from being 

 brought home ; and five anxious days to all concerned 

 intervened before it could be set in its place. In 

 the mean time, the presses and raising machinery had 

 been fitted in the towers above, and the lifting process 

 was begun on the 8th of April, when the immense mass 

 was raised 8 feet, at the rate of about 2 inches a minute. 

 On the 16th, the tube had been raised and finally 

 lowered into its permanent bed ; the rails were laid 

 through it ; and, on the 1 8th, Mr. Stephenson passed 

 through with the first locomotive. The second tube was 

 proceeded with on the removal of the first from the 

 platform, and was completed and floated in seven 

 months. The rapidity with which this second tube was 

 constructed was in no small degree owing to the Jac- 

 quard punching-machine, contrived for the purpose by 

 Mr. Roberts, of Manchester. This tube was finally fixed 

 in its permanent bed on the 2nd of January, 1849. 



The floating and fixing of the great Britannia tubes 

 was a still more formidable enterprise, though the ex- 



