EAST RIVER AXD HELL GATE IMPROVEMENT. 447 



to pass through the roof of the battery -house. A thirty-grain platinum 

 fuse, connected with a small battery at Astoria, was laid on the disk 

 and stuck on with a lump of wax. It had been previously determined 

 by experiment that the blow struck by this fuse on exploding, and 

 transmitted by the iron rod, would be so sharp as to completely pul- 

 verize the tumbler and yet not splash the mercury. 



The mine was flooded by two siphons of twelve and sixteen inches 

 respectively, in fifteen hours and a half, ending at 3.30 a. m., October 

 10th. The explosion was set for 11 a. m., October 10th, but the inter- 

 ests at stake were so great, and the details to be looked after to avoid 

 every chance of miscarriage so numerous, that, in spite of the most en- 

 ergetic effort, everything could not be made ready and tested in time to 

 fire at the appointed moment. The explosion did not actually take 

 place till 11.13. This delay caused some confusion in the seismoscopic 

 observations. 



The whole area of the reef was shattered. The plan of making 

 the excavations large enough to swallow all the debris of the reef and 

 leave a channel deep enough, without further operations, already aban- 

 doned at Hallet's Point as more expensive than dredging up the broken 

 rock, was never entertained at Flood Rock. Hence the sensational 

 view, which many persons expected to witness, of a sudden disappear- 

 ance of the rock, was not seen. Though the charges all exploded at 

 the same instant, the time and the appearance of the effect above the 

 water-surface varied according to the strength of the rock and the 

 depth of the water. There was no loud report and no dangerous 

 shock. The breaking of some panes of glass and the shaking down of 

 a few bricks and loose ceilings constituted all the damage that was 

 done. 



Pending the awarding of a contract for dredging, the work of 

 removing the rock was begun with a scow belonging to the Govern- 

 ment as soon after the explosion as possible. From fifteen to thirty 

 tons of rock were removed daily by being hoisted out after having 

 been slung by divers on chains. A contract has been let for the 

 removal of 30,000 tons of the rock at 83.19 per ton, the contractor 

 to do his own surface-blasting. This is less than the price for which 

 rock was removed on similar terms at Hallet's Point. The contractor 

 has two grapples at work, and is removing an average of about 120 

 tons a day. As a whole, the cost of mining a cubic yard of rock has 

 been reduced 34f per cent from the cost of doing the same work at 

 Hallet's Point. The total cost of the work done on Flood Rock, in- 

 cluding the final blast, amounts to 82.99 per cubic yard of the whole 

 amount of rock broken, or 85.66 less than the cost of breaking Hal- 

 let's Point. A considerable part of this gain will, however, be ex- 

 pended on the proportionately larger amount of dredging to be done. 

 The net result, however, will show an improvement of not less than 

 30 per cent, and probably more. The total cost of the final blast at 



