178 Transactions of the Ameewan Institute. 



had been used, up to this time, more than 2? 500, 000 of tons of 

 stone m its works of masonry, and more than 75? 000? 000 of tons 

 of earth and rock in tlie construction of its channel, more materials 

 than will be used in the building of the 2,000 miles of the Pacific 

 railway. The works for the public supply of water to all our 

 great, and to many of our smaller cities and villages, deserve men- 

 tion. There is hardly a town, especially in the northern section 

 of this country, which has not a public water supply, and the engi- 

 neering works of the most of them have been skillfully executed. But 

 there is no work of this kind in the world which will compare in 

 engineering merit with the Croton, in the designs for its stractures, 

 and their construction in the most skillful and durable manner, with- 

 out unnecessary expenditure, and solely for utility, and at a cost so 

 moderate as to astonish the profession. 



Bridges and Foundations. 



Our American examples of bridges are almost without number, 

 embracing those of nearly every matei'ial and form, and many of 

 them of huge proportions. Among the most noted of these are, the 

 Niagara and Cincinnati, of wire, suspension, by Roebling ; the Havre 

 de Grace, of wood, by Parker ; the cast iron arched bridge at Phila- 

 delphia, by Kneass ; the Victoria (Montreal) bridge, by Stephenson 

 (a duplicate of the Britannia iron girder bridge), with hundreds of 

 others, equally deserving of mention. The submarine works, exe- 

 cuted by our American engineers, have required a degree of science 

 and skill, at least equal to that demanded for^ny European work. 

 The most important of these are the founding of the piers of the 

 Potomac and Croton aqueducts ; of the Havre de Grace and Harlem 

 bridges ; and the foundations of the United States Graving-dock, at 

 Brooklyn. A brief description of the latter will serve to explain the 

 engineering difficulties which were also encountered in the others. 

 This structure weighs 75,000 tons, and is sustained on a quicksand of 

 more than a hundred feet depth. The foundation had to be placed 

 at a level forty feet below that of the sea, and rendered perfectly 

 unyielding. The sea water had to be shut out by massive coffer- 

 dams, which were twice undermined by the pressure of the water ; and 

 the land portions of these dams — subjected to the pressure of the 

 liquid quicksand, of nearly twice the weight of water — repeatedly 

 broke the chain cables by which they were secured (these cables 

 being the best bowers by which our largest men-of-war ride in the 



