THE FORTH BRIDGE. 421 



necessary to adopt another site, and by bringing the point of crossing 

 five miles further down stream to Queensferry, a considei'dble saving in 

 distance was effected in the roate between Ediubargh and Perth. 



The Act for constructing a bridge at Queensferry was obtained in 

 1873. At this point the Firth of Forth is divided by the island of 

 Inchgarvie into two unequal channels, but the depth of water in each is 

 such that a smaller span than 1,700 feet could not be economically adopted 

 for either channel. North of Inchgarvie the maximum depth of water 

 is 218 feet, and south of the same 197 feet. In the former channel the 

 bottom is of hard trap rock, and in the latter partly of rock and partly 

 of extremely stiff boulder clay. It is not the treacherous character of 

 the bed of the Forth, therefore, but the depth of water which precludes 

 the construction of intermediate piers. Pneumatic apparatus is inappli- 

 cable to such depths as 200 feet, and no responsible engineer would care 

 to found the piers of an important structure upon a bottom which he had 

 no means of examining by diviug apparatus or otherwise. 



To the late Sir Thomas Bouch is due the ci-edit of the bold proposition 

 to cross the Forth in two spans of 1,000 feet, and so to avoid the necessity 

 of intermediate piers iu unprecedented depths of water, with all the 

 consequent uncertainties and contingencies. A conti-act for the construc- 

 tion of Sir Thomas Bouch's great suspension bridge was made with 

 Messrs. Arrol, and the preliminary works were in progress when the Tay 

 Bridge fell. In consequence of the latter catastrophe the directors of the 

 Forth Bridge Company decided not to proceed with the works, and an 

 Abandonment Bill was consequently promoted in the Session of 18il. 

 The North British, Great Northern, North Eastern, and Midland Railway 

 Companies, being interested in securing direct comnmnicaiion with the 

 North of Scotland, objected to the abandonment of the enterprise, and 

 instructed their respective consulting engineers, Mr. Fowler, Mr. 

 Harrison, and Mr. Barlow, to, report anew on the practicability and cost 

 of crossing the Forth, either by a bridge or otherwise, at Queensferry or 

 elsewhere. A careful re-investigation of the whole question was accord- 

 ingly made, with the i-esult that the directors were advised that iu was 

 perfectly practicable to build a bridge across the Forth which would comply 

 with all the requirements of the Board of Trade and public safety, and 

 that the best place of crossing was at Queensferry. The Abandonment 

 Bill, which had passed the Commons, was then withdrawn, and the 

 engineers were instructed to agi-ee upon a design. Modifications of the 

 original suspension bridge were first considered, and Mr. Fowler and the 

 author then submitted a project for a bi-idge on the continuous girder 

 principle. Mr. Harrison and Mr. Barlow, fully appreciating the advan- 

 tages which would pertain to such a bridge as compared with a more or 

 less flexible suspension bridge, made independent investigations, and sug- 

 gested several modifications. Finally, the design now before you was 

 unanimously agreed upon by all as the one to be recommended to the 

 directors for adoption. The directors acted upon this recommendation, 

 and, accordingly, the necessary plans were deposited, and an Act was 

 obtained this year for constructing a continuous girder bridge across the 

 Forth at Queensferry, having two spans of 1,700 feet, two of 67 o feet, 

 fourteen of 168 feet, and six of 50 feet, and giving a clear headway for 

 navigation purposes of 150 feet above high-water spring tides. For this 

 work Mr. Fowler and the author are acting as engineers. 



It would probably be conceded by everyone that a girder bridge would 



