CAISSONS. 



263 



iron, with wrought-iron spindles lined with gun metal, and 

 working in gun-metal bearings in cast-iron frames. The rollers 

 have flanges, against which the spear ends of the keels press 



T Pi ATFORM 



PLAN AT PLUMMER BLOCK SEATS. 

 FIG. 266. 



as the caisson is drawn back into the chamber, and so prevent 

 abrasion of the timber meeting-faces. 



The machinery for hauling the caisson into and out of the 



PLAN AT WATERTIGHT DECK. 



PLAN AT TOP OF FLOORS. 

 FIG. 267. 



chamber consists of two endless-chain cables, one on each side 

 attached to the ends of the yoke which is fastened to the caisson 

 by the hauling bar; these cables pass round loose sheaves at 

 the entrance to the chamber, and over two chain- wheels keyed 



