60 Book of Engineering 



thing of a miracle, and if we give it a 

 thought we shall see here one of the greatest 

 achievements in theory carried safely for- 

 ward into practice. 



Years were given to the surveys of these 

 Alpine tunnels, and until they were satis- 

 factory there could be no question of award- 

 ing the contract. 



It is not generally known that the tunnel 

 engineer usually contrives his mountain 

 boring upon an incline, which will not be 

 too great a strain upon the locomotive. 

 Thus there is a point usually half-way 

 where there is a summit. It is shown very 

 clearly where this summit is placed by the 

 laboured breathing of the locomotive becom- 

 ing easier, and then by a perceptible increase 

 in speed as the train starts upon its descent. 

 The extra fuel needed for the ascent is 

 compensated very frequently by the possi- 

 bility of cutting off steam completely for 

 some miles upon the descent. 



In the case of the Alpine tunnels, however, 

 electric locomotives have either ousted 

 already, or are threatening to oust, the 



