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Knight's Mechanical Encyclopedia (ed. Knight), T. (search)
in the tunnel will be 3,873 feet above the sea level, in order to give drainage in each direction; 7 in 1,000 to Goeschenen; and 1 in 1,000 to Airolo. 10 feet daily at each end is the usual rate of progress. The rock is solid at the northern portion, but requires lining and arching at the southern. That already traversed is for the most part mica gneiss and mica schist. The estimated cost is $10,000,000. The work is to be finished within eight years. The boring-machines used are those of Dubois and Francois, the general mode of working being similar to that at Mont Cenis, and the daily progress made appears to be rather more than double. It is feared now (1876) that this work will be abandoned. The Hoosac tunnel, through the mountain of that name, on the railway between Troy, N. Y., and Greenfield, Mass., having a length of 4 3/4 miles, is the longest tunnel in the United States. It is cut through strata of mica slate of varying hardness, and was originally commenced about 185