Description | Photograph of the Forth Bridge under construction, general view taken from Dalmeny Park at water level. With the exception of one detail photograph, this is the only picture secured from the east side of the bridge, owing to the receding chararacter of the shore. Having been obtained from a point at a large angle with the centre line, without being too far distant, it is another suitable view for the purpose of showing the gigantic nature of the span. A very good idea of the shape of the cantilever can be had from this picture, as a few pencil lines joining the upper and lower members with the Queensferry masonry pier show the precise position it will occupy when complete. At her moorings, midway between Inchgarvie and the mainland, lies HMS Devastation, which, though not half-a-mile to the west of the bridge, is scarcely more than a speck, whilst the island and its castle - the highest part of which is 100 feet above the water level - is fast dwindling into insignificance. Another interesting feature of this view is the temporary tie already referred to, which is here very prominent. By reference to No. 1, and the general description of same, it will be seen that the distance from centre of vertical column to the point on the bottom member at which the first tie strikes it, is 180 feet in a horizontal line. Though, owing to their dimensions and general design, these 12 feet tubes were able to support themselves with facility, it was considered expedient to limit the unsupported length, not only on account of its own weight and the cage it carried, but because such provision would forward subsequent operations. The most satisfactory plan that could be adopted for this purpose was to bring into use some of the permanent work already fixed, and with this end in view the method employed was as follows:- At a point in the vertical columns some few feet above rail level were bolted plates, to which was attached a chain (comprised of links which had once played a leading part in the construction of old Hammersmith Bridge) stretching to the extreme end of bottom member and screwed up tight. This chain, however, was not, as commonly supposed, intended to take any considerable strain, but merely to prevent any sag in the tie subsequently constructed. Accurately speaking, therefore, it was a temporary tie to support a permanent one during construction, that actually devised to take the weight off the tube being composed of a portion of top member for Bay 3. Transcription from: Philip Phillips, 'The Forth Railway Bridge', Edinburgh, 1890. |