Scientific Lectures. 179 



lieaviest storms). Fresli water springs, witli a head far greater than 

 that from the sea, again and again undermined the piles (driven 

 nearly forty feet), and forced up large areas of the foundation by 

 their hydrostatic pressure, although heavily loaded. The superstruc- 

 ture of the finest cut granite, in which the slightest yielding would 

 have been perceptible, stands to-day as firm as if founded on solid 

 rock. The Harlem bridge has been mentioned, because of the novel 

 construction of its piers, and a growing opinion, on the part of 

 American engineers, that this system of founding piers in difficult 

 places will, in this country as in Em'ope, supersede those heretofore 

 used. These piers are composed of large cast iron columns, six feet 

 in diameter, fifty feet long, and fifty tons weight each. These enor- 

 mous piles were driven, twenty -five feet deep into the gravel and 

 rocky bed of the river, by the modern invention of the pneumatic 

 process, by which, with a six-horse engine, an air pump, and a dozen 

 men, these huge masses of iron were handled with certainty and ease. 

 I have stood on the platform, and, with a turn of my wrist, sent this 

 fifty tons plunging downward with almost frightful velocity, and then 

 arrested it within the fraction of an inch of any desired depth. The 

 eastern terminus of the Pacific railway at Omaha is now being con- 

 nected with the railways on the east side of the Missouri by a bridge 

 whose piers will be of cast iron columns of eight feet diameter, driven 

 eighty feet below the bed of the river by the same process. 



Machines. 



The civil engineer, however, has been enabled to accomplish some 

 of his most important undertakings, through the instrumentality of 

 the large masses of metal and the workmanship thereon, and by means 

 of the great [tools and engines! with^which he has been furnished 

 by the skill and genius of the mechanical engineer, A mass of bronze 

 or of iron of a ton weight, of specific form and workmanship, was 

 almost, if not quite, unknown before the Christian era. Now we 

 have those in cast iron of frouxvlOO^to 150 tons, and in common use 

 of from forty to sixty tons. In wrought ii'on of thirty to forty tons, 

 and in steel or bronze of twenty-five tons, cast in any desired form, 

 and planed, tm'ned or bored*with an accuracy and finish equal to that 

 of the woi-^s of a delicate Geneva watch. Bessamer has an anvil 

 block of cast iron, made at one casting, of more that one hundred 

 tons, and Krupp has another of one hundred and fifty. But neither 

 of these required the skill which produced the bed-plate of the 



