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rock, so that blasting was necessary. The use of explosives vitiated the air, while the length of the passage and the impossibility of sinking shafts made the ventilation question a vital one. Had the drills been run by steam, the presence of steam-engines constantly generating smoke and gas would have heated and vitiated the air still further. By the new invention the difficulty was met. The air was compressed outside the tunnel, and conveyed into it by pipes. Here a double purpose was served: by its expansion and liberation the air ran the drills, and ventilated the tunnel The invention which makes this practicable is called the Sommeiller machine, from the name of the chief inventor.

In an address delivered before the American Geographical Society in December, 1879, Major S. F. Shelbourne referred to the manner in which the work in the Alpine tunnels was accelerated by inventions. The subject of the address was the San Blas route for an interoceanic canal. To construct a canal at this point, it would be necessary to cut a ship-tunnel seven miles long; and it was the purpose of Major Shelbourne to show that the advances made in the mechanical arts during the building of the Alpine tunnels, made a ship-tunnel much more practicable than was supposed. It may be added that, at the time referred to (1879), three competent American authorities—Major Shelbourne, Walton W. Evans, and Frederick M. Kelley—advocated the San Blas route. Of all the routes proposed, it was the shortest, the distance being thirty-three miles from sea to sea, against forty-six at Panama. After the work had been begun at Panama, however, Mr. Kelley, whose interest in the subject was so great that he spent out of his private fortune $120,000 for surveys upon the Isthmus, became an advocate of that undertaking.

Major Shelbourne said:

In 1863 the progress made in the Mont Cenis Tunnel with hand-drilling, and powder as an explosive, was an average of a foot and a half a day. After they had commenced to introduce power-drilling and the Sommeiller machine, the progress they made was three times greater—that is, four and a half feet per day.

Major Shelbourne next adduced the testimony of Mr. Shanly, the contractor of the Hoosac Tunnel, after observing that in 1872 the Hoosac Tunnel was "in the rush of its progress" under him. Mr. Shanly stated, in 1874: "The use of the machine-drills saved about two thirds of the expense of drilling. The expense of labor would have been, I think, fully three times the cost of machine-drilling." Major Shelbourne next cited the progress effected at St. Gothard, the contract for which was taken in 1872 by Louis Favre, of Geneva:

In the St. Gothard Tunnel, from 1875 to 1877, with the greater perfection of explosives—for they had come to use nitro-glycerine—and by means of improved drills,^[1] they made a progress of five to one, that is to say, they excavated

1. An account of the drills used in the St. Gothard Tunnel may be found in Simms's "Tunneling," pp. 305-320.