PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 905 



the panels, similar to those belonging to the trussary of the chains 

 and top chord. The cross girders are two in nnni])cr for each 

 panel, and are parabolic in form, curving from 18 inches in the 

 centre to 12 inches at the ends, which ends project far enough 

 over the sides to form the cantilevers of the footwalks. These 

 cross girders arc secured to the longitudinal 16-inch beams, which 

 I have before described. Bet^^ecn each pair of cross girders T 

 irons are sprung in segmental arches, feather downwards, having 

 riveted to their plate side corrugated iron. The spandrils thus 

 formed are filled up level with the girders, by means of a light 

 concrete of bitumen and cork, and the whole paved with oaken 

 blocks. This will make a strong and elastic flooring, as well as 

 being impervious to water. The railing of the footwalk is five 

 feet high, formed of light two by one-quarter inch l)ars, latticed 

 together, and riveted at intersections formed by their crossing. 

 Of course, this railway will have to be laterally stiffened at each 

 panel by a suitable strut. So much in general terms for the con- 

 struction of each span, which I hope you fully understand. 



The Central Pier. 

 I wish now to say a few words with reference to the central 

 pier. As to the abutments, they will have to be the same for any 

 bridge, and they therefore require no explanation. A pier has 

 many objectors, and whether their objections are based u})on tena- 

 ble grounds, it remains for me to discuss the effect of a pier in the 

 centre of the river, us well as the problem of construction. I 

 regret exceedingly at not being able to get accurate information of 

 the bed of the East river, in lieu whereof I must assume certain 

 data, such as depth of water, character of bottom, and velocity of 

 currents. Viewing the past, and having that experience to go 

 by, the sinking a pier in a mud bottom, in say sixt}' feet water, 

 with a current of two feet per second, is not a work of unsur- 

 mountable difliculty. Huge wrought iron cylinders, so success- 

 fully used the past few years, could be put in at a comparatively 

 small cost. It may be a matter of interest to recall the sinking of 

 the huge piers for the Saltush l)ridge, by Brunei, Jr. This pier 

 was sunk in 82 feet water, the tide running and falling 18 feet, by 

 means of a wrought iron cylinder, of 37 feet in diameter and 90 

 feet in height, 16 feet of which pierced through the muddy bottom 

 to solid rock. The same process was intended to be applied in 

 sinking the piers of the proposed International bridge at Buffalo. 



