62 Book of Engineering 



advance of the art of tunnelling is so great 

 that in very many instances the roundabout 

 route has now been abandoned in favour 

 of a direct tunnel under the mountains. 



The first of the Alpine tunnels was that 

 known as the Mont Cenis. This was driven 

 by Italian engineers through the Grand 

 Vallon, to link up the Paris-Marseilles rail- 

 way with those serving Turin, a branch line 

 being also constructed to complete the link. 



The first blast was fired in the construc- 

 tion of this tunnel in 1857, and four years 

 later the machine drill was introduced. This 

 led to considerable speeding up; even so, 

 it took another ten years before the trains 

 could pass from France to Italy without 

 hindrance. The length is less than eight 

 miles. How greatly the air drill helped the 

 engineer may be gathered, when it is stated 

 that during the first four years, when all 

 work was done by hand, the progress was 

 only at the rate of 9 inches a day upon 

 either side of the Alps. When the com- 

 pressed air drill was fairly at work 45 inches 

 a day were driven through the granite. 



