(522 THE GREAT ALPINE TUNNELS. 



MONT CENIS TUNNEL. 



The Mont Cenis, or as it is more accurately called, the Frejus Tun- 

 nel, is nearly 8 miles in length. It is for a double line of way, width 

 being- 26 feet and height above rails 20 feet 6 inches. The construc- 

 tion is of excellent character, and it is lined throughout with either 

 masonry or brickwork, except for two lengths of 100 meters and 7<) 

 meters, respectively. In these two lengths solid white quartz was 

 encountered, and two years were occupied in penetrating it. The gal- 

 lery of direction is straight throughout the actual tunnel, being curved 

 away to the portals. 



The system of setting out will be described in more detail when we 

 come to consider the case of the Simplon, but in passing we may 

 remark one peculiarity which does not attach to the other tunnels, viz, 

 that the gallery of direction on the Italian side is shut oh 1 ' by a massive 

 grating from the railway tunnel, and is occupied by guns and Gatlings 

 and by a detachment of artillery, the French portal being commanded 

 by an armor-plated fort. 



The approaches to the tunnel, both on the Italian and French sides, 

 are severe, amounting to 30 per 1,000 or 1 in 33 on the former, and 25 

 per 1,000 or 1 in 10 on the latter. 



Owing to an alteration during construction on the Bardonnechia 

 side, it became necessary to introduce an ascending gradient for about 

 1 kilometer in length at the Italian end of the tunnel, and this has 

 resulted in seriously compromising the ventilation 



A rough diagram will serve to give an idea of the gradients and the 

 consequent difficulty in working the traffic. 



Trains coming from France with an ascending gradient of 1 in 10 

 against them for a length of T kilometers, when followed by a current 

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

 In this tunnel, 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 kilometer 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 cham- 

 bers, 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 con- 

 stant, summer and winter, and is about 19° to 20° C. = 66° to 68° F. 



The altitude of the tunnel is 1,218 feet above sea level, and the 



