Proceedings of the Polytechnic Association. 795 



pumps, each having a cylinder thirteen inches in diameter and twenty- 

 four inches in length, internal measurement. The number of strokes 

 each a minute are eighty. The cylinders and air are cooled by an 

 ingenious mode of injecting cold water into them. 



The occasion of my entering the tunnel was for the purpose of 

 observing the mode adopted there for blasting by nitro-glycerine, 

 which performance takes place every eight hours, night and day. I 

 therefore accompanied Mr. Charles A. Brown, who has charge of every- 

 thing pertaining to this department, dowai the shaft. On the platform 

 at our feet, as we descended, was a basket containing a niimber of tin 

 tubes, with corks in each, holding, altogether, twenty pounds of nitro- 

 glycerine. This basket, I must confess, occupied, chiefly, my thoughts 

 during the descent, notwithstanding Mr, Brown told a humorous 

 anecdote ; and a complication of pipes, braces and bolts formed the 

 sides of the shaft in a manner naturally exciting attention and 

 inquiry. 



These were visible from the light of our tallow candles, adjusted in 

 the fronts of our hats. 



On arriving at the bottom of the shaft, Mr. Brown took the lead 

 toward the drillers, 1,500 feet distant, with the basket of nitro-gly- 

 cerine. When we came to the terminus, the machines were soon 

 stopped. Mr. Brown measured each hole drilled, and made his memo- 

 randa of the depth. 



The two engines were rolled back, over the iron rails laid for this 

 purpose, several hundred feet, and a heavy shield of plank, spiked and 

 bolted together, placed in front of them for the purpose of protecting 

 them, and also the electrician. While this vv^as o-oino; on, Mr. Brown 

 was taking the tubes of nitro-glycerine from his basket, one at a time, 

 withdrawing the cork, and inserting another, in which a fuse, made 

 after the plan of Mr. Abies, was adjusted so as to immerse it in the 

 explosive liquid. Attached to these fiise are two copper wires a few 

 feet long, insulated with gutta percha. The tubes are next inserted 

 in the holes, and pushed with a w^ood cane to the bottom, the insu- 

 lated wires projecting a few inches out of the hole. Coarse, damp 

 sand was next crowded down, and somewhat packed, until the holes 

 were full. 



The two wires of all the fuses were alternately connected to one of 

 the two large insulated wires, which are attached to the sides of the 

 tunnel, and extend about 600 feet from where the blast takes place. 

 The wire at the left was also attached to the other prime wire. All 



