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yd February, 1886. 



Mr. W. H. Patterson, M.R.I.A., in the Chair. 



Professor Fitzgerald read a Paper on 



THE NEW BRIDGE OVER THE FIRTH OF FORTH, 



Which is now in process of erection. 



Having stated briefly the greater difficulties which presented 

 themselves in the task of bridging the Forth than even those 

 which had proved so seriously formidable in the Tay, Prof. 

 Fitzgerald said that the former work when finished will be the 

 largest girder bridge in the world, there being no other bridge of 

 that class having so wide a span. The engineer, Mr. Baker, had 

 very considerable difficulties in selecting a design that could be 

 actually carried out. The great difficulty to be dealt with in 

 constructing bridges of long span is the weight of the bridge 

 itself. By means of steel, though not steel of the ordinary kind, 

 being more like fine wrought iron, that primary difficulty was 

 overcome. In large bridges the weight increases faster than 

 the strength, and the advantage of steel is that it gives greater 

 strength than iron, with the same weight. The entire length 

 of the new bridge will be about one mile, and the main span 

 1,700 feet. The Admiralty required that the bridge should be 

 150 feet above the water. The depth of the water itself is 

 150 feet. The foundations rest on solid rock in some parts, 

 and in others in a peculiar clay. 



The lecturer then entered into a detailed description of the 



