May 10, i888] 



NA TURE 



39 



THE FORTH BRIDGE. 



WE have been enabled, through the kindness of Mr. 

 Baker, to reproduce one of the photographs of 

 the Forth Bridge, showing what is known as the 

 "junction" at the end of bay i, between tie i, strut 2, 

 and the bottom member. 



A general account of the Forth Bridge has rbeen so 



recently placed before the readers of Nature (vol. xxxvi. 

 p. 79), in the lecture by Mr. Baker, on May 20, 1887, 

 before the Royal Institution, that it is unnecessary to 

 cover the same ground again. The progress made in 

 erection since that date is indicated by our engraving, 

 showing the successful completion of the lower portion of 

 the first bay. 



The junction we have illustrated is nothing more nor 



less than the connection of the web of a lattice girder 

 with one of its booms, but here the junction alone weighs 

 as much as an ordinary iron railway bridge of 100 feet 

 span. This mass of steel work is suspended 80 feet above 

 high water, and projects 180 feet beyond the masonry 

 piers. Considerable forces are sometimes needed to bring 

 the tubes into their correct position ; and as in the case of 

 the Britannia Bridge, which on a hot day moves 3 inches 



horizontally and 2^ inches vertically between sunrise and 

 sunset, so here considerable movement takes place during 

 the day, and by careful watching the great tubes can 

 sometimes be caught and retained in proper position, 

 without the intervention of hydraulic or other power. 



The weight of steel employed in the junction now 

 under consideration is about 90 tons. The attachments to 

 the strut and tie are made by means of strong gusset 



