452 



THE MENAI BRIDGE. 



PAKT VIII. 



walls of these main piers were built from within as well 

 as from without all the way up, and the inside was as 

 carefully and closely cemented with mortar as the ex- 

 ternal face. Thus the whole pier was bound firmly 

 together, and the utmost strength given, while the 

 weight of the superstructure upon the lower parts of 

 the work was reduced to its minimum. 



Over the main piers the small arches intended for the 

 roadways were constructed, each being 15 feet to the 

 springing of the arch, and 9 feet wide. Upon these 

 arches the masonry was carried upwards, in a tapering 

 form, to a height of 53 feet above the level of the road. 

 As these piers were to carry the immense weight of the 

 suspension chains, great pains were taken with their 

 construction, and each stone, from top to bottom, was 

 firmly bound together with iron dowels to prevent the 

 possibility of their being separated or bulged by the 

 immense pressure they had to withstand. 1 



The most important point in the execution of the 

 details of the bridge, where the engineer had no past 

 experience to direct him, was in the designing and fixing 

 of the wrought iron work. Mr. Telford had continued his 

 experiments as to the tenacity of bar iron, until he had 

 obtained several hundred distinct tests ; and at length, 

 after the most mature deliberation, the patterns and 

 dimensions were finally arranged by him, and the con- 

 tract for the manufacture of the whole was let to Mr. 

 Hazeldean, of Shrewsbury, in the year 1820. The iron 

 was to be of the best Shropshire, drawn at Upton forge, 



1 To guard against the effects of 

 lateral pressure resulting from this 

 heavy mass of masonry bearing on 

 the arches forming the roadway, six 

 strong wrought iron ties, four inches 

 wide and two inches thick, firmly 

 bolted at each end, were introduced 

 horizontally at the springing of the 

 arches over the carriage ways, and 

 thus any deficiency of strength at that 

 point was effectually provided for. 



Strong cast iron blocks or saddles 

 were placed upon the top of the 

 piers to bear the suspension chains, 

 and they were fitted with wrought 

 iron self-acting rollers and brass 

 bushes, for the purpose of regulating 

 the contraction and expansion of the 

 iron, by moving themselves either 

 way according to the temperature of 

 the atmosphere, without the slightest 

 derangement to any part of the work. 



