Art. IV. — A New Process of Purifying Water discovered 



by M. Birkmyre. 



By Mr. C. R. Blackett. 



[Read May 13th, 1880.] 



Art. V. — The Tay Bridge. 

 By W. C. Kernot, M.A. 



[Read July 8th, 1880.] 



The object of the present paper is to give a brief account 

 of a structure which, from its size and the nature of its 

 construction, is one of the most remarkable in existence, 

 and of a disaster, the consequences of which, in respect to 

 loss of life and destruction of property, are probably with- 

 out parallel in the history of railway engineering. 



The Tay Bridge crosses the Firth of Tay at Dundee, and 

 is a portion of the direct line of railway connecting that 

 city with the more southern parts of Great Britain. The 

 Firth itself is an arm of the North Sea, about 25 miles long, 

 and at the bridge nearly 2 miles in width ; the site being 

 some 10 or 12 miles inland. 



The bridge, which carries a single line of railway of 4-feet 

 8J-inch gauge, is straight for a length of considerably more 

 than a mile, the ends being curved, the northern extremity 

 contiguous to the town of Dundee forming a quadrant in 

 plan. The straight portion lies very nearly north and south. 



The exact length of the structure, as given in the Engi- 

 neer of the 2nd January last, is 3450 yards, or 70 yards 

 less than 2 miles, and is divided into 85 spans, or openings, 

 varying from 29 to 245 feet. The piers numbered 1 to 14, 

 counting from the southern end, are entirely of brick, the 

 remainder being, with a few unimportant exceptions, open 

 frames, consisting of a group of cast-iron columns connected 

 together by wrought-iron bracing. 



The girders are of wrought-iron, with, in most cases, 

 parallel top and bottom members, and a double triangula- 

 tion between at an angle of 45° with the horizontal. 



For the greater part of the length the rails are supported 



