THE MONT CENIS TUNNEL.

Westport Times, Volume V, Issue 765, 19 January 1871, Page 3

THE MONT CENIS TUNNEL.

The following, from " The Artisan" of Oct. 1, will be read with great interest :—The tunnel, as Professor Ahstead reminded the audience, will perforate the crest of the main chains of the Alps, nearly midway between Mont Tebor and Mont Cenis, passing nearly under the summit of Mont Frejus. The operations of the tunnel involve a direct cut through a series of rocks on a line whose depth below the surface was almost at once very considerable. Owing to the form of the ground and tho rise of the mountain, the depth was 2000 feet at each end after 2000 feet tunnelling. From this point, however, the depth increased very little from each end for a loDg distance. In the middle of the tunnel the depth below the surface is 5100 feet, while the deepest borings for such works as mines and wells do not exceed '3OOO feet. The works have been carried on throughout with some regard to the great physical questions involved. Among these the temperature at various distances and depths beneath the surface was not the least important. Instructions were given to bore a large hole laterally into the rock for a distance of about 500 metres, and determine the temperature of the rock by thermometers provided for the purpose. On the northern side this important experiment had been carelessly executed, but on the south side, especially towards the centre, some good observations had been made, and tho result was somewhat startling. The last observation made at the time of his visit was : at 6200 metres (20,342 feet) from the south end, at a depth of more than 5000 feet. The result was 28 deg. C.=Bo£ deg. F. Here again, however, there was still something wanting, the mean annual temperature of the surface not being accurately known, and the depth from the surface of the stratum of permanent temperature never having been determined. With referrence to the progress of the work of tunnelling, the Professor stated that on the 31st of last month there remained less than 2000 feet out of 40,000 feet to pierce, and as the present rate of progress is about 500 feet per month, it may be expected that the communication will be complete by the commencement of the ensuing (this) year.