The Great Bore
A Souvenir Of The Hoosac Tunnel

of Pennsylvania, erected a factory at the west shaft, and from that day till the completion of the work manufactured the only explosive used. After the adoption of nitro-glycerine there were fewer acci- dents from explosion than before, and Professor Mowbray always asserted that with ordinary care it could be handled with perfect safety. I 01 use the explosive was placed in tin cartiidges about one and a half inches in diameter and into one end of which was introduced an exploder. After a num- ber of holes had been drilled in the rock, the car- tridges inserted and connections made with an elec- tric battery, the charges were exploded. The depths of the drill-holes varied from seven to thirteen feet and were just large enough to hold the cartridge, which also varied in length in proportion to the depth of the hole,—a twelve foot hole requiring a cartridge from four to six feet in length. The greatest progress attained any one month in the tunnel by the use of nitro-glycerine was at the cen- tral shaft, when 180 feet were excavated. DEATH, PERIL AND ESCAPES. The peril attending the construction of the tun- nel was constant, the accidents frequent, the escapes many. Miners were killed by explosions at the