XIV INTRODUCTION 



with the construction of the Mont Cenis tunnel in Europe and 

 the Iloosac tunnel in America,, which works established the 

 utility of machine rock-drills and high explosives. The Mont 

 Cenis tunnel was built to facilitate railway communication 

 between Italy and France, or more properly between Pied- 

 mont and Savoy, the two parts of the kingdom of Victor 

 Emmanuel II., separated by the Alps. It is 7.6 miles long, 

 and passes under the Col di Frejus near Mont Cenis: Som- 

 nieiller, Grattoni, and Grandis were the engineers of this great 

 undertaking, which was begun in 1857, and finished in 1872. 

 It was from the close study of the various difficulties, the great 

 length of the tunnel, and the desire of the engineers to finish 

 it quickly, that all the different improvements were developed 

 which marked this work as a notable step in the advance of 

 the art of tunneling. Thus the first power-drill ever used in 

 tunnel work was devised by Sommeiller. In addition, com- 

 pressed air as a motive power for drills, aspirators to suck the 

 foul air from the excavation, air compressors, turbines, etc., 

 found at Mont Cenis their first application to tunnel construc- 

 tion. This important role played by the Mont Cenis tunnel 

 in Europe in introducing modern methods had its counterpart 

 in America in the Hoosac tunnel completed in 1875. In this 

 work there were used for the first time in America power rock- 

 drills, air compressors, nitro-glycerine, electricity for firing 

 blasts, etc. 



There remains now to be noted only the final development 

 in the art of soft-ground submarine tunneling, namely, the use 

 of the shield and metal lining. The shield was invented and 

 first used by Sir Isambard Brunei in excavating the tunnel 

 under the River Thames at London, which was begun in 1825, 

 and finished in 1841. In 1869 Peter William Barlow used an 

 iron lining in connection with a shield in driving the second 

 tunnel under the Thames at London. From these inventions 

 has grown up one of the most notable systems of tunneling 

 now practiced, which is commonly known as the shield system. 



