THE ST. GOTHARD TUNNEL. 533 



it was dangerous to work for fear the mass would fall and bury the 

 workmen, and cut off their retreat. Communication was opened be- 

 tween the two galleries on the 29th of February, 1880. The chief 

 miner on the southern (Airolo) side had pierced an horizontal hole about 

 ten feet long, and had caused the attacks from the side of Goeschenen 

 to be suspended on his penetrating to the northern gallery. Proceed- 

 ing with a boring of moderate depth, he reduced the thickness of the 

 remaining mass to about four feet. Preparations were made for the 

 final attack by piercing four holes in the center of the boring, and 

 eleven other holes at equal intervals around it and not very far distant 

 from it. The explosion opened a passage of a little more than thirty 

 inches in diameter, through which the engineers and some of the work- 

 men were able to go over from one gallery to the other. When the 

 communication was first opened, at eleven o'clock in the morning, the 

 barometer stood .150 of an inch higher at Goeschenen than at the 

 southern end of the tunnel. A current of air was immediately pro- 

 duced in the gallery, which blew at the opening at the rate of a metre 

 and a half (nearly five feet) a second. A few hours later the relative 

 pressure was reversed, and the barometer stood .039 of an inch lower 

 at Goeschenen than at Airolo. The direction of the current of air was 

 consequently changed ; it blew from south to north, but at the rate of 

 only about a foot in a second. The actual length of the tunnel was 

 about twenty-five feet shorter than the calculated length. The differ- 

 ence in the level of the two galleries was not more than four inches, 

 and their lateral deviation was not more than eight inches. According 

 to a statement made by M. Colladon to the Academy of Sciences at 

 Paris, the most efficacious means adopted to speed the work of exca- 

 vation were the diking of the torrents and the application of water 

 collected in aqueducts as a moving power to turbine-wheels requiring 

 high falls, the adoption of air-compressors which worked with great 

 rapidity, the cooling of the air in the compressors, at the moment of 

 compression, by the injection of water in a fine spray, th*e use of dyna- 

 mite, and the determination which was adopted from the beginning to 

 carry on the excavations from the top of the tunnel. By the aid of 

 these improved methods the advance through the hard rocks was made 

 with double the speed that the engineers in charge had been able to 

 attain in boring the Mont Cenis Tunnel. It is estimated that, notwith- 

 standing its greater length, the tunnel of St. Gotharcl when completed 

 will have cost from twenty-five to thirty per cent, less than that of 

 Mont Cenis. 



The provisions for conducting compressed air into the galleries, 

 involving a system of pipes upward of sixteen thousand feet long in 

 each gallery, afforded excellent opportunities for studying the flow of 

 compressed air through metallic conduits. The loss of air in passing 

 through the pipes was an important factor. The absolute pressure of 

 the air, which was equivalent to six and a half atmospheres at the 



