200 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



aid of a large caisson and compressed air was proposed by 

 M.M. Zschokke and Terrier, and approved by the Council of 

 Public Works. 



The work to be executed consisted of three parts, First, 



FIG. 186. 



the lengthening of the dock ; secondly, the removal and recon- 

 struction of the pumping station; and thirdly, the sinking of 

 the pump wells and their connection with the dock. 



Fro. 187. 



Extension of the Dock. The first operation was to construct 

 a temporary wall across the dock at the springing of the circular 

 head, capable of resisting the full head of water (Fig. 186). 



