EDITOR'S TABLE. 



10; 



THE HELL-GATE EXPLOSION. 



The series of operations which re- 

 sulted in the blowing up of the great 

 rocky reef at Hallett's Point on Sun- 

 day, September 24th, must be regarded 

 as the most brilliant piece of scientific 

 engineering that has yet been accom- 

 plished. General Newton formed his 

 plans, and entered upon the work in 

 July, 1869. For over seven years he has 

 been preparing for a grand experiment 

 to occupy but a few seconds, and so ac- 

 curately did he calculate, and so com- 

 plete was his command of the irresisti- 

 ble forces to be called into action, that 

 the experiment proved completely suc- 

 cessful, and affords an impressive illus- 

 tration of the prophetic power that is 

 conferred by a knowledge of the ele- 

 ments and forces of Nature. It was 

 the physicists and chemists who long 

 ago worked quietly and obscurely in 

 their laboratories, with little reference 

 to practical ends, and animated only by 

 the desire to acquaint themselves with 

 the laws of the natural world, that 

 paved the way for the great engineer 

 to do this important service for the in- 

 terests of New York and the commerce 

 of the world. 



The reef at Hallett's Point, which 

 has formed such a dangerous obstruc- 

 tion in the Hell-Gate channel as greatly 

 to hinder navigation through Long Isl- 

 and Sound, was of an irregular crescent 

 shape (as shown in the figure), some 



700 feet long, and extending out 300 

 feet into the channel, with an area of 

 about three acres. The rock is a tough, 



hornblende gneiss, with veins of pure 

 quartz, and lies in strata of various de- 

 grees of inclination. The plan of opera- 

 tions was to build a coffer-dani on the 

 rock near the shore to bar out the 

 water, to sink a shaft to the requisite 

 depth, to honey-comb the whole rocky 

 mass by excavation, and then to blow 

 up the shell by charges of dynamite in 

 the roof and supporting columns, to be 

 fired by the agency of galvanic bat- 

 teries. The shaft was sunk to a depth 

 of 33 feet below the line of low water, 

 and ten tunnels were then opened to 

 distances varying from 31 to 126 feet. 

 The cubic contents of the rocky mass, 

 above the depth of 26 feet, at mean low 

 water, amounted to 51,000 yards. The 

 tunnels radiating from the shaft varied 

 from 7 to 22 feet in height, and from 

 9 to 12 feet in width, and, as they ad- 

 vanced, the height rapidly decreased, 

 owing to the downward slope of the 

 surface of the reef. As the main tun- 

 nels diverged from each other, sub- 

 sidiary tunnels were introduced, and a 

 system of transverse galleries was ex- 

 cavated (as shown in the figure), and 

 which left 172 supporting pillars of 

 variable dimensions. The total length 

 of tunnels was 4,857 feet, and the length 

 of galleries 2,568 feet, making the en- 

 tire length of passage excavated 7,425 

 feet. The excavations being completed, 

 so that the roof of rock above was re- 

 duced to a thickness of from 8 to 16 

 feet, the preparation for the explosion 

 began by drilling the rock for the 

 charges. The whole number of blast- 

 holes drilled into the roof and piers 

 was 4,427, varying from 7 to 10 feet 

 in depth, and from 2 to 3 inches in di- 

 ameter. Each one of these holes was 

 charged with three kinds of explosives, 

 all compounds of nitro-glycerine, viz., 

 dynamite, rendrock, and vulcan-powder, 

 in separate cartridges or canisters. 

 Fifty thousand pounds of these explo- 

 sives were buried in the apertures. 

 Ninety-six galvanic batteries, of ten 

 cells each, were employed to ignite the 

 charges. The firing-point was 050 



