ON THE NEW TAY VIADUCT. 885 
the railway, and the greater part of the parapets of the Esplanade spans 
is erected. At the viaduct proper the cylinders for fifty-eight out of the 
total of seventy-three piers have been sunk. The method adopted by 
Messrs. Arrol, the contractors for the works, for sinking them is specially 
ingenious. It consists of a rectangular pontoon, having at each of its 
corners vertical wrought-iron tubular legs, which can be raised or lowered 
hydraulically, When these are lowered to the bed of the river the 
pontoon can be raised out of the water, and thus form a stage for the 
machinery, materials, and men required in sinking and filling the cylinders. 
In the pontoons are two openings, within which the cylinders are pitched 
and adjusted in position. The excavation is effected by means of steam 
diggers, and as the digging proceeds the cylinders follow down, until the 
required depth is reached. When the sinking and filling is completed, 
the supporting tubes or legs are raised from the bottom, and the pontoon 
floated into position for another pier. It may be mentioned that, in 
raising or lowering these legs, great use is made of the tide. Four of 
these pontoons have been used for sinking the cylinders. The wrought- 
iron structures or shafts of four piers on the south side, and of twenty- 
four piers on the north side, have been erected. The girders for one 
span on the south side and nine spans on the north side are erected in 
position on the piers, and nearly all the girders, except those for the 
large spans, are built and ready for erection. The girders and flooring 
for each of the thirteen large spans are being built entire on a staging 
erected for this purpose at the south end of the viaduct, and arrange- 
ments are being made by which the girders and flooring for each span 
complete will be floated out to position in the viaduct, and placed on the 
eylinders ; they will then be raised hydraulically to their proper height, 
the wrought-iron shafts of the piers being built up at the same time. 
The general progress of the whole viaduct may be briefly stated to be as 
follows :—Nearly seven-eighths of the foundations of the eighty-six piers 
are put in; almost one-half of the piers are built up to the level of the 
girders, &c., and out of the total length of 3,600 yards, 540 yards—i.e. 
rather more than one-eighth—is complete and ready for the railway. All 
the wrought-iron and steel for the work is carefully tested, the tests 
being that the wrought-iron must be capable of bearing a tensile strain 
of 22 tons per square inch, with an extension of 6:25 per cent. in a 
length of 8 in.; and the steel 27 tons per square inch, with an extension 
of 15 per cent. The whole of the iron and steel work is shaped and 
drilled at Messrs. William Arrol & Co.’s works at Glasgow, preparatory 
for erection either on the shores or in position in the viaduct. In 
_ executing these works a great amount of plant is required, and a number 
of ingenious machines and clever contrivances have been devised and 
brought into operation by the contractors for the better performance of 
the work and saving of labour. 
