628 THE GREAT ALPINE TUNNELS. 



minutes; drilling, one and three-fourths to two and one-half hours; 

 charging and firing, fifteen minutes; clearing away debris, two hours; 

 or a total of between four and one-half to five and one-half hours, 

 resulting in an advance of 3 feet 9 inches, or a daily advance of 

 nearly 19 feet <> inches. 



The progress of each of the two faces during the month of April last 

 has averaged IT feet 3i inches per day. and is a remarkable corrob- 

 oration of the speed estimated by the engineers four years ago. The 

 estimate was as follows: 



Daily progress at each face: *eet. 



First year 8. 85 



Second year 17. 22 



Third year 19. 1 8 



Fourth year 21. 32 



Fifth year 31. 16 



The work is now in its second year, so that the estimated speed is 

 being exceeded. In other words, the tunnel is being driven through 

 granite at a higher speed than is attained in London clay. 



Water power is abundant, and the waters of the Rhone are har- 

 nessed to the work, whilst those of the Diveria provide the power at 

 Iselle. 



Views are given of the intake from the Rhone, the concrete aque- 

 duct, the metallic conduit pipes, 3 feet, and 3 feet 3 inches in diameter, 

 which carry a pressure of 250 pounds to the inch. The further neces- 

 sary increase in pressure is obtained by high-pressure pumps in the 

 power house. 



It was at one time intended to sink a 20-inch bore hole from the 

 village of Berisal to the tunnel, a depth of some 2,400 feet, for the 

 purpose of delivering water at high pressure for the works. This 

 may still be done, hut the meandering of the tool might result in the 

 awkward dilemma of having to search for it, in solid rock, below 

 ground. 



Some few years ago a rather amusing incident occured in connec- 

 tion with a tunnel, which is worth recording. A certain railway com- 

 pany were constructing a tunnel beneath and nearly at right angles to 

 an existing tunnel of one of the large English railway companies. As 

 the legal formalities were not actually completed, the engineers were 

 requested to stay proceedings until all was in order, and they instructed 

 the contractors accordingly, but the latter were anxious not to incur 

 any delay, and they quietly and surreptitiously continued to drive 

 their heading through. The engineer of the existing railway suspected 

 this, and sank a bore hole on the center line of the new 7 work, expect- 

 ing his tool would, at the correct level, drop into the heading, at a 

 depth of To feet. The contractors looked for a similar result, and 

 therefore placed a sheet of steel on the roof of their drift, so that the 



