376 Transactions of the American Institute. 



tons, or nearly twice as much as from both the other sources of 

 support 



As I have very fully described the method of accomplishing this 

 result, in a paper which has been sent to London for publication, 

 and in another, Avhich will soon be published in this country, I 

 refrain from again describing it, but will furnish it to any person 

 interested. In some previous discussions, questions were raised 

 whether iron piles or columns would withstand the pressure of the 

 intense frosts of our climate, and the shocks from vessels, rafts or 

 ice. 



When these columns are carried above water, filled with concrete 

 and capped on top, they are efiectually sealed against the admission 

 of w^ater; but if by any circumstance, it should obtain admission, 

 its expansion in freezing would be first exerted in compressing the 

 concrete filling, which has but one-tenth of the power of resistance 

 possessed by the iron shell. In Scotland and Northern Eussia, as 

 well as at Harlem, no injury has ever resulted from this cause. 



In regard to the second objection, there is but one case on record, 

 w^here any injury has been caused b}' a very severe blow, and it hiis 

 since been ascertained that it arose in consequence of one of the 

 castings being defective. 



The repeated experience at the Chepston bridge over the Severn, 

 the Charring Cross and several others in Europe, besides those over 

 the Pedee, Santee, Savannah and Harlem rivers, show conclusively, 

 that they are well adapted to resist the most severe shocks that 

 -will ever be brought against them, and that' they are as well 

 adapted for this purpose as the firmest stone piers. 



When it becomes necessary to use the pneumatic process to 

 remove obstructions from beneath, the columns must be not less 

 than twenty-four, and perhaps thirty inches, exterior diameter. 



In this case a conical working chamber of six feet in diameter, 

 would be found very convenient, and a column of that form can 

 be driven with equal, or perhaps greater facility, than a cylindrical 

 one. 



The hydrostatic process has been repeatedly used, under certain 

 circumstances, with greater economy than the pneumatic; either by 

 forcing the water into them, from a natural head, or by a force 

 pump, and driving the water and wnth it the interior soft material 

 to the outside, or through the syphon-pipe before described. 



When the column is passing through a close material like clay, 

 its descent may be very much facilitated by using at different 



