S78" -. REPORT—1885. 
columns and made to carry the load. The water is now allowed to escape, 
and as there is a back pressure in the cylinders similar to that in those 
used for raising the main platform, the rams are forced into the cylinders, 
and being secured to the lower cross girders are made to raise these also. 
This action will be repeated till all is raised to the desired height, when 
the girders will be quickly secured to the points previously prepared for 
their junction with the bracing in the vertical planes. 
In addition to the several parts of the bridge already mentioned, the 
cantilevers will form a leading subject for careful thought. The proposed 
method of their erection is, however, beyond the scope of this paper, and 
I need only remark that all concerned see their way to successfully 
overcoming this part of the work also. 
The approach viaducts on both sides of the Firth are presently in a 
forward state of progress; the girders on the south side, immediately 
over the water, being practically complete, having been built on timber 
staging, the top of which was on a level with the stone piers, so far as 
completed, or about 18 feet above high water. These girders will be 
raised to the level of the next stage erected on shore, on which will have 
been built during the time occupied in that lifting another pair of girders 
to which the first portion of the viaduct will be connected. This raising 
and joining to other portions still higher up will be continued till the full 
height is reached, when all the ten spans will be complete. 
The north viaduct is in a more forward state than the south, it being 
wholly completed with the exception of a few of the end bays, which 
cannot be put in position till a higher point has been reached. The whole 
of the north viaduct piers are on land of a very undulating character. 
This necessitated some of their number being raised a considerable height 
so that a uniform level throughout might be attained, and all the girders 
built at the same time on a stage similar to that used for the other 
side. 
The piers provide points from which the lifting can be easily and 
safely done. Various proposals for effecting this were discussed ; that 
finally sanctioned by Sir John Fowler and Mr. Baker is to place under- 
neath the end pillars of the main girders on each pier a temporary cross 
girder extending between and beyond these, and bearing up the whole 
weight, on timber blocking resting directly on the pier. In each of these 
temporary cross ‘girders are placed two hydraulic cylinders, one being 
directly underneath each main girder; in both, the ram faces downwards. 
Each cylinder is provided with a separate valve to regulate its action in 
raising. When at rest the temporary cross girders will transmit their 
load to the piers, either through the blocks placed close to but between 
the lifting cylinders or those outside and nearer the ends of the piers, this 
being determined by the point at which building has to be carried on. If 
in the centre then the supports are outside, and vice versd, the ram when 
lifting will bear on a prepared sole of hard wood spreading somewhat over 
the stonework. Great care must be exercised to keep the different bear- 
ings in the whole viaduct as near one uniform level as possible during the 
lifting operations, to avoid any undue straining of the main girders. As 
soon as the structure has been raised the full stroke of the cylinders, a 
new lift will be commenced, the blocks on which the rams bear having, 
however, been previously packed up. The height required to give ample 
clearance for building underneath will be about four feet. 
At the ends of the north viaduct, in lieu of a bearing on the piers, 
