The time required to complete the work, without the aid of machinery, was estimated by the Commissioners at eleven years and four months; and with the aid of such machine drills and power as had already been applied with success at Mt. Cenis, at seven years and a half. The work at Mt. Cenis was commenced in 1857, and up to July, 1861, 2142 feet had been excavated by hand labor; the machine drills were then applied, and the Italian government has recently announced that the work will be finished by the close of the year 1870. It will be seven and a half miles long. The Hoosac Tunnel will be about four and a half miles long, and at the present time it has been excavated 4675 feet, and shafts have been sunk to the depth of 575 feet. The machine drills will be applied in a few days; but they are drills which will do twice, and possibly three times the work of those at Mt. Cenis. To the sound judgment, energy, and untiring perseverance of Mr. Brooks, and the inventive genius and skill of Mr. Stephen F. Gates, of Boston, and Mr. Charles Burleigh, of Fitchburg, belongs the credit of perfecting a pneumatic drill, by means of which our great tunnel will be completed much within the time named by the Commissioners, and with a reduction of their estimate of its cost by hand labor of several hundred thousand dollars. We have seen this drill operated by compressed air, at the rate of two hundred blows a minute, each blow given with a force of more than five hundred pounds, cut an inch and a quarter hole in a block of Hoosac rock, thirty-eight inches in thirteen minutes, without changing its points. Its superiority over the Mt. Cenis drill consists in its lightness, automatic feed, and smaller size. The Mt. Cenis drill is eight feet long, and weighs six hundred pounds, and the whole machine moves forward in feeding. The Hoosac drill is four feet long, weighs two hundred and eight pounds, and can be handled by two men. In feeding, the drill alone advances, and in such manner as to accommodate itself to any kind of rock it may encounter, whether hard or soft. Its points are sharpened in a die by half a dozen blows of the hammer. It will do the work of twenty men; and, finally, sixteen of them can be applied to a surface upon which only nine of the Mt. Cenis drills can be used. The operation of this drill has already been witnessed by hundreds of persons, among them machinists, engineers, and stone masons, and not one of them entertains a doubt that it will do all which is claimed for it by the inventors. But the carriages are nearly ready, and these little machines will shortly be put to their work. The friends of the Tunnel have no fears of the result. * * * * *