In the basement of the machine-shop are two compressors. The first was put in January, 1866. It has four cylinders 13 inches in diameter, and 20 inches stroke. This compressor is used to drive the drills, and furnish air for the blacksmith shop. The second compressor was put in some time in October. It has four cylinders 25 inches in diameter, and 24 inches stroke, and is used for ventilation one-fourth of the time, two hours after each blast, viz., from 8 to 10, A. M., from 4 to 6, P. M., and from 12 to 2, A. M. The compressors work satisfactorily. The loss of power in the transmission of air from the machine-shop to the drills, a distance of 4,500 feet, being hardly perceptible. In addition to the compressors, there is in the machine-shop the following machinery, viz.: three lathes, one of them worked by hand; a drilling machine; a planer; a bolt-cutting machine and a saw-table. Sixty horse-power is required to carry the machine-drills, the machines in the shop, and to furnish air for the blacksmith shop. When the large compressor is used, 75 additional horse-power is required. A circular saw at the east end of the machine shop, is occasionally used, driven by power derived from the turbine wheels. The blacksmith shop, near the entrance of the tunnel, contains three forges. The hand-drills are made, and, together with the machine drills, sharpened at this shop. The ordinary repairs of the drilling machines are done in the machine shop. New parts of the same are furnished from Fitchburg. The heading in the tunnel at this end when driven by hand was about 15 feet wide by 6 feet high. When driven by the machines it is 16 feet wide and 8 feet high. Its location is in the centre of the tunnel, 4-1/2 feet above subgrade, and 1-1/2 feet above the road bed. The force employed at this point in July last was-- Mechanics in iron, 4 Engine-men, 2 Masons, 10 Manual labor, 58 Engine and compressor men, including firemen, 6 Carpenters, 5 Blacksmiths and helpers, 8 Statisticians, 2 Runners of machine-drills, 6 Sawyer, 1 Manual laborers, 63 --- Total in July, 165