INTRODUCTION XV 



In closing this brief review of the development of modern 

 methods of tunneling, to the presentation of which tin- ir- 

 mainder of this book is devoted, mention should be made of 

 a form of motive power which promises many opportunities fur 

 development in tunnel construction. Electricity has long 1 <-fii 

 employed for blasting and illuminating purposes in tuni.rl 

 work. It remains to be extended to other uses. For hauling 

 and for operating certain classes of hoisting and excavating 

 machinery it is one of the most convenient forms of power 

 available to the engineer. Its successful application to rock- 

 drills is another promising field. For operating ventilating 

 fans it promises unusual usefulness. 



