TOULON DOCK. 



183 



length on the west side by a cul- 

 vert leading to the well, placed 

 about 50 feet back from the coping 

 (Fig. 167). 



Toulon Graving Dock (Figs. 168 

 to 170). The conditions obtaining 

 at the port of Toulon were such 

 as to render the ordinary methods 

 of dock construction inapplicable. 

 To meet the difficulties of the case, 

 two courses were proposed by Mr. 

 Hersent, the engineer. First, to 

 construct the entire dock within a 

 large iron caisson with a flat and 

 rigid bottom. The caisson would 

 be gradually lowered as the ma- 

 sonry was laid within it, and finally 

 rest upon the bed, which would 

 be previously prepared for it with 

 great care. Secondly, to construct 

 the dock within a similar caisson, 

 but with the addition of working 

 chambers beneath, which would be 

 utilized ~by means of compressed 

 air, for forming the bed. By 

 such means, the bed on which the 

 dock would ultimately rest could 

 be more carefully prepared and 

 levelled, and a uniform bearing 

 over the whole surface ensured. 



The second proposition appeared 

 to be the most advantageous, and 

 was therefore adopted. 



The caisson was of sufficient 

 size to enclose the whole of the 

 masonry ; the total length was 472 

 feet 6 inches, the width 134 feet 

 6 inches, and the depth 62 feet 4 

 inches. 



1 Engineering, vol. xxvi. p. 503. 



