RAILWAY CONSTRUCTION. 37 



in a straight line, with easy gradients, falling towards the 

 entrances, efficiency of drainage has been secured, and excessive 

 strain on motive-power avoided. The approaching valleys on 

 each side were in some places too irregular and broken to admit 

 of zigzag loops, and the spiral tunnels were adopted instead. 

 The enlarged plan of two of the spiral tunnels will explain the 

 method of working. An ascending train enters the first tunnel 

 at A, and after passing round almost an entire circle, on a rising 

 gradient, emerges at a much higher level at the point B. 

 Proceeding onward, the train enters the second tunnel at C, and 

 after passing round a similar circle, on a rising gradient, comes 

 out at a still higher point, D, and continues its course up the 

 valley. 



The last five sketches illustrate some of the methods which 

 have been adopted when constructing railways through some of 

 the most difficult mountain ranges. They show what has been 

 done, and may serve as guides in working out the location of a 

 line in some hitherto unexplored region. 



Gauge. The gauge of a railway, or its width from inside to 

 inside of rails, affects both its cost and efficiency. If the gauge 

 be exceptionally wide, then the expenditure on works and rolling- 

 stock will be proportionately heavy ; and although theoretically 

 the extra wide gauge may possess greater capabilities for 

 accommodation and high-speed travelling, we may find in 

 practice that the necessary requirements may be provided on a 

 much more moderate gauge. On the other hand, if the gauge be 

 exceptionally narrow, there will be diminished convenience both 

 for passengers and merchandise, and a corresponding limit to the 

 speed in transit. 



In isolated districts, where passenger traffic is of secondary 

 importance, and where the principal merchandise will be heavy 

 without being bulky, such as mineral ores, slates, etc., a com- 

 parative narrow gauge may possibly suit the purpose. For 

 main trunk lines, however, where a large, heavy, and fast 

 passenger traffic will have to be worked, and where goods of all 

 kinds, many of them bulky without being heavy, will have to be 

 carried, an ample gauge must be selected to ensure convenience 

 and safety. A liberal gauge permits the use of commodious 

 rolling-stock without any great amount of lateral overhanging 

 weight outside the wheels ; whereas with a narrow gauge there 

 is the tendency if not the necessity to use vehicles which 



