94 ANNUAL OF SCIENTIFIC DISCOVERY. 



stone was a porous sandstone. When struck with a hammer it 

 fell to pieces readily, and revealed a series of seams running 

 through it. There was no mixture of slate or granite, or any of 

 the harbor kinds of stone in it. 



Of the 23 tons of powder used, about half was contained in 

 English ale casks, double-coated with a heavy pitch varnish inside 

 ancT outside so as to be water-proof. The other half of the pow- 

 der was in 7 boiler tanks of wrought iron, firmly bolted, the larg- 

 est measuring 8 feet in length and 2 feet in diameter. The bar- 

 rels were placed close to the side of the excavation, near the 

 junction of the arch or roof with the floor, so as to blow away 

 the arch from the lowest point of the excavation reached. They 

 were placed resting on their sides. The 7 boilers were laid 

 through the centre of the chamber, the largest in the middle, 

 where the roof was highest. This disposition was made to 

 equalize the force on each part of the rock. A perforated piece 

 of gas-pipe, 2 feet in length, charged with fine gunpowder, ran 

 into each barrel from the end, with a piece 6 feet long into the 

 boilers, charged in the same way. These different tubes were 

 connected with insulated electric wires, which passed from one 

 barrel to another, the end in each tube consisting of a fulminat- 

 ing cartridge. 



The insulated electric wires connecting the barrels were encased 

 in gutta-percha. When the powder was arranged in the excava- 

 tion, and the connections made secure, this wire was drawn up 

 through a tube in the shaft, and placed on board a bark situated 

 about~l,000 feet from the rock. Here it was connected with an 

 electric battery. The coffer-dam was then removed, and the 

 water permitted to fill up the excavation, and so act as a tamp- 



ing. 



It being understood that the blast would be fired on the 23d of 

 April, a very large concourse of people gathered to witness it. 

 Everything appears to have worked properly, and the explosion 

 threw a column of water and rock, 100 feet in diameter, 100 feet 

 into the air. It is believed the operation has been entirely suc- 

 cessful, and that the rock will give no further trouble. ^ 



The method employed seems very ingenious, and is, so far as 

 we are aware, entirely novel. Scientific American. 



REMOVAL OF THE HELL-GATE OBSTRUCTIONS. 



The work of removing these noted obstructions to navigation is 

 continued unremittingly night and day. Eight "galleries" or 

 chambers have been commenced. These run in various directions 

 under the reef, all converging to a common centre at the point 

 of beginning. They are named after distinguished men. Those 

 furthest advanced are " Grant," "Sherman," "Humphries." They 

 all front the great excavation, which is GO by 100 feet in size, and 

 30 feet from the mean low-water mark to the floor line. " Grant" 

 gallery has been pierced to a distance of 32 feet directly under the 

 most formidable spur of the reef. These tunnels are to be ex- 



