CHAP. VII. OVER THE THAMES AT LONDON. 365 



45 feet wide in the centre, increasing to double that 

 width at the abutments. It was to contain 6500 tons of 

 iron, arid the cost of the whole was to be 262, 289/. 



The originality of the design was greatly admired, 

 though there were many who received with incredulity 

 the proposal of bridging the Thames by a single arch, 

 and it was sarcastically said of Telford that he might as 

 well think of " setting the Thames on fire." Before any 

 outlay was incurred in its construction, it was deter- 

 mined to submit the design to the most eminent scien- 

 tific and practical men of the day ; after which evidence 

 was taken at great length before a Select Committee 

 which sat on the subject. Amongst those examined on 

 the occasion were the venerable James Watt of Bir- 

 mingham, Mr. John Eemiie, Professor Hutton of Wool- 

 wich, Professors Play fair and Robison of Edinburgh, 

 Mr. Jessop, Mr. Southern, and Dr. Maskelyne. Their 

 evidence will still be found interesting as indicating the 

 state at which constructive science had at that time 

 arrived in England. 1 There was a considerable diver- 

 sity of opinion amongst the witnesses, as might have been 

 expected ; for experience was as yet very limited as to 

 the resistance of cast iron to extension and compression. 

 Some of them anticipated immense difficulty in casting 

 pieces of metal of the necessary size and exactness, so as 

 to secure that the radiated joints should be all straight 

 and bearing. Others laid down certain ingenious theories 

 of the arch, which did not quite square with the plan 

 proposed by the engineer. But, as was candidly observed 

 by Professor Playfair in concluding his report "It 

 is not from theoretical men that the most valuable in- 

 formation in such a case as the present is to be expected. 

 When a mechanical arrangement becomes in a certain 

 degree complicated, it baffles the efforts of the geometer, 

 and refuses to submit to even the most approved methods 



1 The evidence is fairly set forth in ' Cresy's Encyclopedia of Civil Engi- 

 neerin' ). 475. 



