248 



ENGINEERING. 



had been driven 1,010 metres, and the one on 

 the west side of the mountain 710 metres. The 

 tunnel is expected to be completed in five years 

 from the commencement of the work. 



The ventilation of long tunnels is a problem 

 with which engineers have not yet dealt suc- 

 cessfully. The natural mode of ventilation is 

 the outflow of the warm air at the higher 

 opening of the tunnel, and the inflow of cool 

 air to supply its place at the other mouth. As 

 the air within the tunnel is always warmer 

 than the external atmosphere, natural ventila- 

 tion takes place continually. Differences of 

 temperature, of atmospheric pressure and 

 moisture, and the direction of the prevailing 

 wind, may increase the natural ventilation, or 

 they may impede. A tunnel might be made 

 with a sufficient difference of level at the two 

 ends to insure complete ventilation, were it 

 not that steepening the grade would necessitate 

 the generation of more smoke, and thus aggra- 

 vate the principal evil which it is sought to 

 remedy. The ventilation of the Mont Cenis 

 Tunnel is most imperfect, because unfavorable 

 natural conditions of the external atmosphere 

 almost neutralize the natural draught, notwith- 

 standing the great difference of level at the 

 two extremities, which is nearly 460 feet. The 

 clouds of smoke which the engines leave in the 

 tunnel roll backward and forward. The me- 

 chanical means which are employed to expel 

 them are incapable of securing an effective 

 ventilation. The air-compressing machines 

 barely drive a current as far as the refuge- 

 chamber sufficient to clear it of smoke; and 

 the apparatus tried for pumping out the viti- 

 ated air has proved a comparative failure. 

 The natural process of ventilation may be ac- 

 celerated by either rarefying the air at the 

 npper end of the tunnel, or by condensing it 

 at the other. An artificial method of rarefying 

 the air in the tunnel at the end where the cur- 

 rent finds its natural egress has often been 

 tried. Shafts are sunk into the tunnel at each 

 end, and fires are kept burning to heat the air 

 in one shaft, and thus cause an in-draught of 

 fresh air through the other. One objection to 

 this method for long Alpine tunnels is the ex- 

 pense of the apparatus and fuel when it is em- 

 ployed on such a large scale. Another objec- 

 tion is that the radiation of heat from the walls 

 of the tunnel is so great as to render it desir- 

 able that the air should not only be renewed, 

 but that it should be as cold as possible. The 

 plan of cooling the air in the other shaft has not 

 yet been tried. Wilhelm Pressel advocates em- 

 ploying this method instead of the other. He 

 proposes to cool the air in one of the shafts by 

 means of falling water. Mountain-streams of 

 icy temperature are always accessible at the 

 approaches of Alpine tunnels. He believes 

 that a fall of about one hundred gallons a sec- 

 ond through the shaft would cool the air suf- 

 ficiently, and create a difference of temperature 

 between the shafts sufficient to establish a 

 current. A difference of 10 centigrade, he 



thinks, would effect this object. The mouths 

 of the tunnel and the openings of the shafts 

 would have to be closed at will sufficiently to 

 prevent the disturbing effects of wind on the 

 ventilation. In cold weather the artificial re- 

 frigeration would be unnecessary. 



The spiral tunnel at Leggestein, completed 

 in the spring, was the first made and the prin- 

 cipal one of a number of tunnels of the kind to 

 be bored on the St. Gothard Railway. The 

 plan adopted for the roads leading to the en- 

 trances of the great bore was to follow as far 

 as possible the windings of the valleys of the 

 Reuss, on the north side, and of the Ticino, on 

 the south side of the mountain. This scheme of 

 keeping in the valley-bottoms rendered it nec- 

 essary to carry the line through considerable 

 vertical distances by means of spiral tunnels, 

 in which the gradient is steep and the curve 

 sharp. The Leggestein Tunnel has a gradient 

 of 23 in 1,000, and describes a curve of 300 

 metres. After leaving the tunnel, the railroad 

 winds around the mountain, passing through a 

 shorter tunnel above. The work of tunneling 

 was exceedingly difficult, as the rock was hard 

 granite, and, owing to the entire absence of 

 water, the boring had to be done by hand. 

 There are two other tunnels of this kind being 

 bored in the Reuss Valley, that of Wellington, 

 which is also bored by hand, and that of Pfaff- 

 ensburg, each of which is 1.000 metres long. 

 On the Ticino side there are four of these 

 spiral or turn tunnels, from 1,500 to 1,600 me- 

 tres in length. 



The first passenger-train passed through the 

 St. Gothard Tunnel on November 1st; time, 

 fifty minutes. The tunnel exceeds the Mont 

 Cenis Tunnel in length by 8,856 feet, being 9 

 miles long. Goeschenen, the northern end, is 

 elevated 3,637^ feet above the sea-level. The 

 tunnel ascends in a gradient of 1 in 171 for 

 24,600 feet, and then 1 in 1,000 for 4,428 to 

 the highest point, 3,785 feet above the sea. It 

 keeps this level for 1,279 feet, and then descends 

 with a gradient of 1 in 200 for 3,870 feet, and 

 1 in 500 for 13,792 feet. The station at Airolo 

 is 3,755 feet above the level of the sea. The 

 normal width of the tunnel is 24 feet 11^ 

 inches at the level of the rails, and 26 feet 3 

 inches, 6 feet above. The height is 20 feet. 

 The roof is semicircular. The floor slopes 

 with a fall of 2 per cent from each side to a 

 drain 271 inches deep in the center. The line 

 has also 52 subsidiary tunnels which, with the 

 main tunnel, have an aggregate length of six- 

 teen miles. There are 64 bridges and viaducts 

 whose combined length form one per cent of 

 the length of the line, while 17 per cent is 

 taken up by the tunnels. The main tunnel is 

 laid with two tracks of 4 feet 8 inches 

 gauge. 



The experimental works on the British 

 Channel Tunnel have proved satisfactory. Two 

 shafts were sunk on the English side, one at 

 Abbot's Cliff, and one at Shakespeare Cliff. 

 From the first a gallery was driven by ma- 



