1818.] across the Mersey, at Runcorn. 17 



basis, as seen on a larger scale in Fig. 7, and to which, and to 

 the basis, the suspending rods are attached by any ordinary 

 mode, or as shown in Figs. 9 and 10. 



V, the convex cast-iron plates laid on the wrought-iron frame- 

 work, and attached to each other ; but, if thought necessary, 

 not to the framework, to allow for the difference of expansion 

 between cast and wrought-iron. 



W, in Fig. 7, shows the same plates on a larger scale, and 

 laid down across the road, so as under a pressure always to abut 

 uaainst each other, and not against the sides of the road. 



Fig. 4, elevation of part of the centre of the bridge on an 

 enlarged scale, showing the suspending rods as jointed; the 

 railing or parapet, &c. 



This parapet railing is so contrived, chiefly by means of the 

 hollow pyramidal pillars, Z, Z, as to admit of the expansion of 

 the wrought-iron frame and cast-iron parapet, independently of 

 each other. Thus the parapet railing is attached to a strong 

 cast-iron plinth or blocking course (see Fig. 6), which is cast to 

 lit the outer rib of the frame, without being screwed to it, but 

 with projections which pass under, or catch on the small cross 

 ribs, so as to prevent the possibility of overturning. 



The hollow pillars are firmly fixed by screws, and each has a 

 vertical opening, equal to that of a vertical section of the 

 parapet. In these openings, as in mortices, the ends of each 

 length or division of the parapet are inserted as tenons without 

 being fixed ; and of course the wrought-iron framework may 

 thus expand by heat, or be deranged by a strain, with no other 

 effect than drawing the parapet a few fines out of the mortice, or 

 the cast-iron parapet may expand, inserting itself a few lines 

 further, Sec. as the case may be, without the slightest injury to 

 the fabric. Fig. 16 is a horizontal section of one of the pyra- 

 midal pillars, with the ends of the parapet railing so inserted. 



Fig. 5, enlarged surface plan, or vertical profile of the road, 

 in which Z, Z, are the pyramidal pillars X, X, single iron 

 rods for the protection of the footpath, and the cast-iron block- 

 ing-course, or abutment, 8cc. to the parapet. 



Fig. 6, enlarged section. (See Fig. 5. 



Fig. 7, enlarged view of one of the wrought-iron frames com- 

 posing the road. 



W, convex plates laid on ditto. (See descriptions of Figs. 1, 

 2, and 3.) If it is desired to form the road of timber, then only 

 the outer part of this frame is to be used, and all the rest framed 

 and covered with fir or oak planking, &c. 



Figs. 8, 9, and 10, enlarged view of the rods forming the 

 basis of the road. 



Y, (in Fig. 8,) the plate to which the cross ribs of the frame, 

 Fig. 7, are attached as at Fig. 9. 



Z, screw boxes of a particular construction, to tighten the 

 rods in the first erection, and afterwards if required. 



Vol. XI. N° I. ii 



