SCHUYLKILL PERMANENT BRIDGE, 



which he had himself constructed. The building com- 

 mittee where thus left to struggle through every diffi- 

 culty, unaided by any person practically acquainted with 

 such work ; and with no scientific assistants. They de- 

 pended solely on the workmen, who had gained some 

 experience at the eastern dam, for the farther execution 

 and fortunate completion of the work ; which they faith- 

 fully performed. It is not surprising that the committee 

 should, after all other schemes were considered, and 

 found fallacious and impracticable, be fully sensible of 

 the risque and difficulty of attempting anew and untried 

 undertaking. In their report of the 3 1st December 

 1802 they thus express themselves. 



used at the piling- of the foundations of the western abutment and wings, 

 were less ; being of about 500 pounds They moved quickly, did more 

 work, and required less power to move them ; but the piles were smaller. 

 The machinery of the engine at the dam, was moved in the usual way, 

 seen in large horse mills, by four horses, on a floating stage, anchored 

 near the dam. There were several parts, ingeniously, and uncommonly, 

 contrived. The ram was elevated by a 6 or 7 inch rope, which was 'vjhite ; 

 because tared yarn was found more inflammable, and otherwise unfit. The 

 friction (though the sheave, over which it moved, was of 18 inches diame- 

 ter) was so great, as to excite a heat, which consumed the hemp inter- 

 nally, when the surface appeared soimd, and felt cool: so that the best 

 rope soon failed; and chains, never so neatly formed, would not answer. 

 The ram could be drove to 60 strokes in an hour ; but 40, were found as 

 many as were, with prudence, admissible. The rope was worked by a, 

 vertical cyllinder; on the principle of the capstan and leading block. This 

 cyllinder was thrown out of gear, by a simple operation, produced by the 

 weight of the ram ceasing to act on it, when detached from the traveller 

 It then (being operated upon by the weight of the traveller) performed a 

 retrogade motion, so as rapidly to unwind the rope ; and the traveller in- 

 stantly followed the ram, in its descent. As soon as the tongs had seized 

 on the ram, the cyllinder was again in its place, and progressed in its dut} -. 

 The horses, relieved when fatigued, constantly proceeded, with a steady, 

 but somewhat quick pace. 



