CHAP. V. ON BRIDGES IN SCOTLAND, 57 



design which was carried into effect. The river Tay 

 being subject to sudden floods in one of which a former 

 bridge had been swept away it was necessary to take 

 every precaution with the foundations, which were got 

 in by means of coffer-dams. That is, a row of piles was 

 driven into the bed of the river, on which a quantity of 

 " gravel and even mould earth mixed together " was 

 thrown in all round the piles, with a view to render the 

 enclosed space impervious to water. Pumping power 

 was then, applied, and the bed of the river laid dry 

 within the coffer-dam thus formed, after which the 

 gravel or clay was dug out to a proper depth, until a 

 solid foundation was secured for the piers. Piles were 

 driven into the earth under the intended foundation- 

 frame, and the building proceeded upward in the usual 

 way. 1 The bridge is a handsome structure, consisting 

 of seven principal arches, and is about 900 feet in 

 length, including the approaches. It was completed 

 and opened for traffic in 1772, and has proved of great 

 service to the locality. 



Smeaton's employment at Perth on this occasion in- 

 troduced him to a considerable amount of engineering 

 business in the North. He was consulted at Edinburgh 

 respecting the improved supply of water for that city, 

 and at Glasgow about the security of its old bridge. 

 But the most important work on which he was employed 

 in Scotland, about this time, was the designing and con- 

 struction of the Forth and Clyde Canal for connect- 

 ing the navigation of the eastern and western seas. 

 The success of the Duke of Bridge water's Canal had 

 directed public attention in all parts of the kingdom to 

 the formation of similar lines of internal communica- 

 tion ; and the movement had also extended to Scotland. 



1 It may be worthy of remark 

 that John Gwin, the person recom- 

 mended by Mr. Smeaton to conduct 

 the trial borings for the foundations, 

 took with him two experienced men 



from England to conduct the works, 

 stipulating that they should each re- 

 ceive wages at the rate of 14s. a 

 week. 



