MECHANICS AND USEFUL ARTS. 29 



"weight of ovei' 100 tons, forced the huge shaft downward into the 

 bed of the lake with inconceivable force. Thus a depth was 

 reached and secured, at which it became perfectlj^ safe to carry- 

 forward the excavation, and complete the shaft to the level at 

 which the tunnel was to begin. The loose rubble-stone is finally 

 to be taken out of the water-tight compartments, one at a time, 

 and they will be re-filled with piers of solid masonry, laid in hy- 

 draulic cement, and united above the surface in some manner, so 

 as to present an immovable front on all sides against the force of 

 storms. 



Both shafts having been completed, the excavation of the tun- 

 nel was commenced from both ends. The work was commenced 

 at the lake end about October, 1865 ; and the tunnel was finished 

 about Nov. 25, 1866. One-third of the length from the shore end 

 at the rate of about 17 feet a day, or about 3,200 feet, was com- 

 pleted before the commencement of the boring from the lake end. 

 About four-fifths of the tunnel was made from the shore side ; the 

 three intermediate cribs and shafts, at first proj^osed, were omit- 

 ted, and all the work carried on by the shafts at each end ; the 

 floor of the crib at the lake end Avas made of 12-inch timber in- 

 stead of plank. 



The clear width of the tunnel is five feet, and the clear height 

 five feet two inches, the top and bottom arches being semi-circles. 

 It is lined with brick masonry eight inches thick, in two rings or 

 shells, the bricks being laid lengthwise of the tunnel, with tooth- 

 ing joints. The bottom of the inside surface of the bore at the 

 east end is 66 feet below the water-level, and has a gi'adiial slope 

 towards the shore of two feet per mile, falling four feet in the 

 whole distance, to admit of its being thoroughly emptied in case 

 of repairs, the water being shut off at the crib by means of a gate. 

 The work has been laid in brick eight inches thick all round, well 

 set in cement. The lower half of the bore is constructed in such 

 a manner that the bricks lie against the clay, while in the upper 

 half the bricks are wedged in Ijetween the brick and the clay, 

 thus preventing any danger which might result from the tremen- 

 dous pressure which it was feared might burst in the tunnel. 



The work was continued night and day, with but sligjit inter- 

 mption, and at all seasons. A narrow railway was laid from the 

 foot of each shaft, as the work pi'ogressed, Avith turn-out cham- 

 bers for the passage of meeting trains ; and small cars, drawn by 

 mules, conveyed the excavated earth to the hoisting apparatus, 

 and brought back at every trip a load of brick and cement. The 

 men worked in gangs of five, at the excavation; the foremost 

 running a drift in the centre of the tunnel, about two and a half 

 feet wide, the second breaking down the sides of the drift, the 

 third trimming up the work to proper shape and size, and tl)e last 

 two loading the earth into the cars. The bricklayers followed 

 closely, only a few feet behind the miners. About 125 men were 

 employed in this work, in three relays, working eight hours each ; 

 the only cessation being from 12 o'clock Saturday night, to 12 

 o'clock Sunday night. A current of fresh air was constantly 

 forced through the tunnel by machineiy. It is remarkable that 

 3* 



