532 



THE POPULAR SCIENCE MONTHLY. 



air apparatus of Professor Colladon, of Geneva, which had already been 

 used at Mont Cenis. Water was obtained in great abundance and of 

 strong fall at Goeschenen from the river Reuss. The supply of water 

 at Airolo was not so abundant. The river (the Ticino) has not a rapid 

 descent, and a very long canal would be required to procure a sufficient 

 fall from it. A torrent, the Tremola, was chiefly relied upon, but the 

 supply from this fell short at times, and had to be supplemented by an 

 auxiliary supply from the Ticino. The force of the stream was applied 

 to turn four turbine wheels which made three hundred revolutions in a 

 minute, and exerted a force of about two hundred horse-power. These 

 wheels were made to turn an horizontal axis with cranks revolving eighty- 

 five times a minute, which kej)t the compressors in operation. The air, 

 subjected to a compression of from four to eight atmospheres, became 

 very hot, and had to be cooled by special applications of water circu- 

 lating in cold currents around the pumps and in the pistons and piston- 

 rods, and by injections of fine spray. After being further cooled and 

 freed from water in suspension by passing it through reservoirs, it was 

 conducted into the tunnel by tubes which were of considerable size at 

 the beginning, but were diminished to correspond with the diminish- 

 ing expenditure of air as the work was advanced. 



The borings were begun by first cutting out a gallery about eight 

 feet square at the top of the intended excavation. "When this advance 

 boring was completed, it was enlarged on the right and left. The 

 arches of the roof were then built, and a trench nearly ten feet wide 

 was dug to the level of the tunnel's base. This was called the " di- 

 nette de Strosse." All that remained on the right and left of the 



Fig. 2. System of Excavation: 1, advance pillory; 2, side-workings; 3, 4, "dinette de 



Strosse " ; 5, " Strosse." 



trench, called the " Strosse," was next removed. Thus, most of the 

 digging was done downward. The work was interfered with at times 

 by the infiltration of water, which, as it did not affect dynamite and 

 soon stopped, was not considered serious ; by rocks of exceptional hard- 

 ness ; and by a bed of loose material in the Goeschenen end, in which 



