Page:Whymper - Scrambles amongst the Alps.djvu/90

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chap. iii.

ments, and mists or clouds concealed the points at the moments they wished to observe them. A single fact will give some notion of the nature of their work. Seven angles had to be measured from the summit of La Pelouse, 10,170 feet above the sea. The observers—who were lodged in the chalets of La Rionda, had to ascend to the summit for seven successive days, and it was seldom possible to measure two angles in the same day."

"The importance of these observations is readily comprehended, and I have described them at some length, because they form the base of the enterprise. One thing is notable. It is the personal care that the engineers have taken. M. Grandis directed the tracing of the line, the triangulation, and the levellings; he assisted at these operations; he selected the bases and points at which 'signals' were to be placed; and all was done under his eye by the engineers, Borelli, Copello, Mella, and Mondino."

On account of the peculiar situation of the ends of the tunnel, two small, connecting, curved tunnels will have to be made. "The construction of these terminal curves is naturally neglected for the establishment of the two false mouths in the direction of the general line."

"The length between the two false mouths is 12,220.00 mètres.
The entry on the side of Italy is at a height of 1335.38 "
" " France " 1202.82 "

Difference of level 132.56 "

This difference of level is overcome by a gradient of 222 in 10,000, which rises from the French entry to the centre[1]

= 135.64 "

A gradient of 1 in 2000, which rises from the Italian entry to the centre[1]

= 3.06 "

132.58 "

  1. 1.0 1.1 The summit will be a few feet higher than M. Conte states, the gradients having been increased since the commencement of the works.