428 Mr Francis Fox [May 25, 



40 against them for a length of 7 kilometres, when followed by a 

 current of air in the same direction, produce a most disastrous state 

 of things. In this, as in all other steep tunnels, engines having a 

 heavy load behind them, go through with their regulator full open, 

 ejecting great volumes of smoke and steam which travel concurrently 

 with the train, and the inconvenience and discomfort produced are 

 very great. 



At each kilometre in the tunnel a refuge or " grande chambre," 

 is provided for the men, and this is supplied with compressed air, 

 fresh water, a telephone in each direction out, a medicine chest, 

 barometer, and thermometer. 



The custodians of the tunnel go in pairs, and if one man is 

 affected by the want of oxygen or dense smoke, the other can render 

 assistance or telephone for further help. The men can retire into 

 these chambers, close the door, turn on the air, and wait either for 

 the tunnel to clear or for a locomotive to fetch them out. 



The temperature in the middle of the tunnel remains nearly 

 constant, summer and winter, and is about 19° to 20° C. = 66° to 

 68° Fahr. 



The altitude of the tunnel is 4248 feet above sea-level, and the 

 height of the mountain above the tunnel is 5428 feet : the tempera- 

 ture of the rock is greatly influenced by this latter fact. 



The question of the temperature of the rocks passed through in 

 the construction of a tunnel is one of great interest, as it depends 

 upon several conditions: (1) the character of the rock; (2) the in- 

 clination of the beds — those which attain a vertical or nearly vertical 

 position being less able to confine the heat than those which are more 

 or less horizontal ; (3) the height of the mountain above the tunnel, 

 or in other words, the thickness of the blanket. 



A diagram is shown (see Fig. 5), giving the temperature actually 

 encountered in the St. Gothard and Arlberg Tunnels, and from these, 

 aided by the carefully prepared geological section along the centre 

 line of the Simplon Tunnel, an approximate line (in red) is given 

 of the temperatures which are expected. 



The possibility of cooling the rocks and the air of the tunnel will 

 be dealt with later on, but there is in addition a permanent lowering 

 of the temperature after the tunnel is complete, particulars of which 

 will be given under the description of the St. Gothard. 



For each 144 feet of superincumbent rock or earth the increase is 

 found to be 1° Fahr. 



The St. Gothard Tunnel. 



This, which is at present the longest railway tiymel in the world, 

 is 9* 3 miles in length, and constitutes the summit of the " Gothard 

 balm." that is, the railway which runs from Lucerne to Chiasso on 

 the Italian frontier. There are about 100 tunnels in all, most of 



