ON THE FORTH BRIDGE WORKS. 877 
The raising of the main platform by the hydraulic cylinders placed 
within the 12-foot rising columns will be performed thus. Water will 
first be admitted to the lower end of two of the hydraulic cylinders in one 
or other of the sloping planes, sufficient to ease the main lifting girders. 
and the two upper cross girders within the columns. The pins through 
these cross girders and the channels of the columns being withdrawn, 
water is again admitted and made to raise the one end of both main lifting 
girders one foot ; when this is accomplished the same pins are reinserted, 
and the load again transferred to the cross girders. The water in the 
lower end of the cylinders now being allowed to escape, that in the small 
annular space at the other end, and which is constantly acting as a back 
pressure, raises the cylinders and with them the lower cross girders to the: 
same position relative to the upper girders which they occupied before 
the lifting operations began. As the pin holes in the four lifting channels 
run the full height, the point to which the platform may be lifted at any 
one shift is a matter of expediency. This lift in most cases will be about 
16 feet, but in any case it will be effected by single lifts of one foot ata 
time, as already described. 
It will be apparent that the manner of lifting at the different points in 
each platform is exactly similar. The cylinders being in line with the 
12-foot rising columns and made to raise the platform to all intents ver- 
tically, induces a slight rocking motion, which is provided for in the cylin- 
ders by planing their bottom surfaces to a very obtuse angle, the apex 
of which is slightly rounded off to form a better bearing, 
As the platform is raised the girders in line with the sloping planes 
will be slid towards the centre of the bridge, each pair on either side 
being always kept as near as practicable atan equal distance from the centre- 
of the rising columns, 
The raising and riveting will thus be carried on till the whole arrives. 
at the top of the pier, the platform being then in a convenient position on 
which to build the top members extending between the columns in line. 
with the bridge. These will now be built, and with them the top junc- 
tions or connecting portions of the upper part of the steel pier, resembling 
in many respects the lower junctions termed the skewbacks, All will be 
riveted in position by the machines already referred to. 
After the main platform has passed the point at which the internal 
viaduct is joined to and made to form an integral portion of the bracing 
in the vertical plane, the lifting of the girders, &c., of which this part is 
composed (and previously riveted complete) to its position will then be 
commenced. This will be done by means of four complete sets of columns, 
girders, and hydraulic cylinders. The cylinders will be placed within 
and fixed to the upper of two cross girders sliding on and temporarily 
bolted to the two vertical columns at each corner of the part to be raised. 
Passing between and extending across from one set of columns to the other 
will be the carrying girders, resting on the top of the upper cross girders 
and bearing the portion to be lifted into position. The ram will be made 
to point downwards and bear against the top of the lower cross girder. 
When water is admitted to the upper end of the cylinders, the bolts in the 
higher cross girders meanwhile having been withdrawn, the rams are. 
forced against the lower cross girders, but as these are securely fixed to. 
the columns, the hydraulic cylinders with the cross girders, carrying 
girders, and structures to be raised are bodily lifted upwards. When 
sraised about one foot the upper cross girders are again fixed to the 
