TUNNEL 37 "extension of full-sized tunnel." The bids accepted for the latter item were as follows : east end section, per cubic yard, $11 ; central section from shaft, $14 ; west end section (part soft ground), $12 ; for arching part of the tunnel with brick, per thousand of bricks laid, $22. The total price agreed on for the work specified by the contract was $4,594,268, the whole to be done by March 1, 1874. At this time Mr. Latrobe resigned as consulting engineer; and that post, after the successive resignations of James Laurie and Edward S. Philbrick of Boston, is now (1876) held by Thomas Doane. The work was vigorously attacked by the Messrs. Shanly at all points. The Burleigh drills and compressors were used throughout their contract with excellent re- sults. Under their patronage, the manufacture of nitro-glycerine (previously used in the tun- nel) was carried on and improved by George M. Mowbray of North Adams. The east heading met the one driven east from the central shaft on Dec. 12, 1872; the west heading met the one driven west from the shaft on Nov. 27, 1873 ; the errors in alignment and levels were astonishingly small, especially as the former meeting was at a distance of 1,563 ft., the lat- ter of 2,056 ft., from the shaft, down which the plumb lines had to be carried over 1,000 ft. The Messrs. Shanly concluded their contract and effected a final settlement Dec. 22, 1874. In- dependently of the contract taken by them, an agreement was entered into between the state and B. N. Farren, on Nov. 19, 1874, to do cer- tain arching and enlarging at the eastern portal of the tunnel. By authority of an act passed by the legislature in 1874, a commission of ex- perts, comprising Prof. T. Sterry Hunt of Boston and Prof. James Hall of Albany as geologists, and Thomas Doane, Josiah Brown, and Daniel L. Harris as civil engineers, was appointed to examine and report on the amount of arching that would be still necessary. Their reports are embodied in that of the commission of 1875, as is also a report from Edward S. Phil- brick, consulting engineer, recommending an additional amount of 1,600 ft. of arching, be- sides that included in the Shanly contract. "Work on this arching is still (March, 1876) in progress. Under a law of 1874 a board of cor- porators of the Boston, Hoosac Tunnel, and Western railroad was created, who reported that the tunnel had up to that time cost the state about $14,000,000. By a subsequent act of 1874 the corporators were superseded by five directors, to whom the interest of the state in the tunnel and railroad was transferred. The next tunnel in the United States in which machine drills were introduced with effect, after their practicability had been demon- strated at Hoosac, was the Nesquehoning tun- nel in Pennsylvania, constructed under the direction of J. Dutton Steele as chief engineer. (See paper by J. Dutton Steele in " Transac- tions of the American Society of Civil Engi- neers," 1871.) Here the Burleigh drill and ordinary black powdr were used. The Mus- conetcong tunnel, on the Lehigh Valley rail- road extension through New Jersey, was the next heavy piece of work in the eastern states on which machine drilling was adopted. This tunnel was begun in April, 1872, and finished in June, 1875, under the charge of Robert H. Sayre, chief engineer and general superinten- dent of the Lehigh Valley railroad company. Charles McFadden of Philadelphia took the contract, and completed what has been con- ceded to be one of the heaviest pieces of tun- nel work ever attempted in America, and yet one of the most rapidly built. Every modern appliance was used. The Ingersoll drill was adopted, about 26 being kept on hand, and from 16 to 18 in constant use. Four Burleigh com- pressors supplied the air required at the west end, and four Eand and Waring compressors at the east. Dynamite was used throughout as an explosive, and gave entire satisfaction. Very heavy difficulties were encountered in the pro- secution of the work, owing to the large bodies of water met with. The total length of the tunnel was a little less than one mile. It was begun by sinking a slope to grade on the west- ern side of the mountain, about one third of the distance through, virtually dividing the tunnel into one third of soft ground working at the west, and two thirds of very hard ground at the east. The headings were started east and west from the bottom of this slope in November, 1872. The east heading had been started in July, 1872. Owing to the heavy cutting necessary at the west end, the head- ing could not be connected with those from the slope, and from a shaft subsequently sunk, until November, 1873. In May, 1873, BO heavy a body of water was struck in the slope heading going east, that it could not be con- trolled. The miners were driven out, and the slope half filled. The water undermining the props and backing of the timbering in the slope, part of the roof fell in, and the work at that point had to be abandoned temporarily. A shaft was then sunk west of the slope, and headings were driven east and west to tap and draw off this water. Here again new and even heavier bodies of water were encoun- tered, resulting in great expense and much loss of time. Finally the difficulties were overcome, the water tapped, and work re- sumed on the original slope heading going east, which met the east heading coming west in December, 1874, the errors in alignment and level being less than half an inch. (For further details on the construction of this tun- nel see a paper by Henry S. Drinker in the " Transactions of the American Institute of Mining Engineers," vol. iii.) With the admira- ble and delicate instruments now so readily obtainable, it would require a positive effort of carelessness on the part of the engineer to en- tail any serious error in tunnel surveys. Espe- cially noticeable among instruments are those recently perfected by Messrs. Heller and Bright-
