ITNNKI.S THCorOH HAHI l: K 97 



difficulty to the powerful Brandt rock-thills, which work under 

 ahead of 8,2w> ft. of water. 



The temperature of the rock depends not only on the depth 

 from the surface, hut largely upon the general form of that sin- 

 face combined with the conductivity of the rock. Taking 

 these points into consideration with the experience gained from 

 the construction of the St Gothard tunnel, 95 F. was esti- 

 mated as the probable maximum temperature, owing to the 

 height of Monte Leone (11,660 ft), which lies almost directly 

 over the tunnel axis. 



Survey After having determined upon the general position 

 of the tunnels, taking into consideration the necessary gra- 

 dients, the temperature of the rock, and a large bed of trouble- 

 some gypsum on the north side, two fixed points on the 

 proposed center line were taken, one at each entrance of tunnel 

 No. 1, and the bearings of these two points, with reference to 

 a triangulation survey made in 1876, were calculated sufficiently 

 accurately to determine, for the time being, the direction of 

 the tunnel. In 1898, a new triangulation survey was made, 

 taking in eleven summits, Monte Leone holding the central 

 position. This survey was tied into that of the Wasenhorn 

 and Faulhorn, made by the Swiss Government, and the accuracy 

 was such that the probable error in the meeting of the two 

 headings is only 6 cms. or _ I ins. 



On the top of each summit is placed a signal, consisting of 

 a small pillar of masonry founded on rock, and cap|>ed with a 

 sharp pointed cone of /.inc, 1 ft. <> ins. high. An observatory 

 was built at each end of the tunnel in such a position that three 

 of the summits could be seen, a condition very difficult to fulfill 

 on the south side owing to the drpth of the gorge, the moun- 

 tains on either side Ixung over 7,000 ft high. Having taken 

 the angles to and from each visible signal, and therefrom having 

 calculated the direction of the tunnel, it was necessary to fix, 

 with extreme accuracy, sighting-pom to on the axis of the tunnel, 

 in order to avoid sighting on to the surrounding peaks for each 



