420 CROSSING THE MENAI STEAIT. CHAP. XIX. 



saving of from 25,000/. to 30,OOOZ. would have been 

 effected. He also said he had arrived at the conclusion 

 that in railway works engineers should endeavour as far 

 as possible to avoid the necessity of contending with the 

 sea ; l but if he were ever again compelled to go within 

 its reach, he would adopt, instead of retaining walls, an 

 open viaduct, placing all the piers edgeways to the force 

 of the sea, and allowing the waves to break upon a 

 natural slope of beach. He was ready enough to admit 

 the errors he had committed in the original design of 

 this work ; but he said he had always gained more 

 information from studying the causes of failures and 

 endeavouring to surmount them, than he had done from 

 easily- won successes. Whilst many of the latter had 

 been forgotten, the former were indelibly fixed in his 

 memory. 



But by far the greatest difficulty which Robert 

 Stephenson had to encounter in executing this railway, 

 was in carrying it across the Straits of Menai and the 

 estuary of the Conway, where, like his predecessor 

 Telford when forming his high road through North 

 Wales, he was under the necessity of resorting to new 

 and altogether untried methods of bridge construction. 

 At Menai the waters of the Irish Sea are perpetually 

 vibrating along the precipitous shores of the Strait ; 

 rising and falling from 20 to 25 feet at each successive 

 tide ; the width and depth of ; the channel being such as 

 to render it available for navigation by the largest ships. 

 The problem was, to throw a bridge across this wide 

 chasm a bridge of unusual; span and dimensions of 

 such strength as to be capable of bearing the heaviest 

 loads at high speeds, and at such a uniform height 



1 The simple fact that in a heavy 

 storm the force of impact of the waves 

 is from one and a-half to two tons per 

 square foot, must necessarily dictate 



Mr. K. Stevenson (Edinburgh) regis- 

 tered a force of three tons per square 

 foot at Skerryvore, during a gale in 

 the Atlantic, when the waves were 



the greatest possible caution ' in ap- | supposed to run twenty feet high, 

 preaching so formidable an element, i 



