MECHANICS AND USEFUL ARTS. 67 



SUSTAINING POWER OF PILES. 



THE following rule for calculating the weight that can be safely 

 trusted upon a pile, driven for the foundation of a heavy structure, is 

 communicated to the Journal of the Franklin Institute by Major Sanders, 

 U. S. Engineer : 



A simple empirical rule, derived from an extensive series of experi- 

 ments in pile-driving, made in establishing the foundation for Fort 

 Delaware, will, doubtless, prove acceptable to such constructors and 

 builders as may have to resort to the use of piles, without having an 

 opportunity of making similar researches. I believe that full confidence 

 may be placed in the correctness of this rule ; but I am not at present 

 prepared to offer a statement of the facts and theory upon which it is 

 founded. 



Suppose a pile to be driven until it meets such an uniform resistance 

 as is indicated by slight and nearly equal penetrations, for several suc- 

 cessive blows on the ram ; and that this is done with a heavy ram, (its 

 weight, at least, exceeding that of the pile,) made to fall from such a 

 height that the force of its blow will not be spent in merely overcoming 

 the inertia of the pile, but, at the same time, not from so great a height 

 as to generate a force which would expend itself in crushing the fibres 

 of the head of the pile. In such a case, it will be found that the pile 

 will safely bear, without danger of further subsidence, " as many times 

 the weight of the ram , as the distance which the pile is sunk the last 

 blow, is contained in the distance which the ram falls in making that 

 blow, divided by eight." For example, let us take a practical case in 

 which the rani weighs one ton and falls six feet, and in which the pile 

 is sunk half an inch by the last blow ; then, as half an inch is contained 

 144 times in 72 inches, the height the ram falls, if we divide 144 by 8, 

 the quotient obtained, 18, gives the number of tons which may be 

 built with perfect safety, in. the form of Avail, upon such a pile. 



DESTRUCTION OF THE MINOT ROCK LIGHT-HOUSE. 



THIS celebrated pile light-house, erected upon Minot's rock, the outer- 

 most of the Cohasset rocks, distant 20 miles from Boston, was entirely 

 destroyed, by a terrific storm, on the 17th of April, 1851. The gale 

 which swept away the structure was one of the most violent and long- 

 continued ever known upon the New England coast. The light on the 

 Minot was last seen from Cohasset on Wednesday night, the 16th. At 

 1 o'clock, Thursday morning, the 17th, the light-house bell was heard on 

 shore, one and a half miles distant; and this being the hour of high 

 water, or, rather, the turn of the tide, when, from the opposition 

 between the wind and the tide, the former blowing on shore, and 

 the latter receding from the shore, it is supposed the sea was at its 

 very highest mark ; and it was at that hour, it is generally believed, 

 that the light-house was destroyed : at daylight nothing of it was 

 visible from the shore. The two assistant keepers were lost : the prin- 

 cipal keeper had left the light-house before the commencement of the 

 storm, and escaped the fate of his companions. 



