496 KEPOKT — 1891. 



sating advantages in the speed of the trains, or the more 

 economical maintenance of the road. 



Let us consider the narrow gauge under the following 

 heads, viz. : — 



Economy of construction. 



Maintenance of the road. 



Cost of rolling-stock. 



Expense of working the traffic. 



First as to constructive cost : — 



Gkades. 



The economy in earthwork at distance that may be effected 

 by the introduction of steep grades is dependent on the power 

 of the engines to be used. 



It is unnecessary here to argue that the reduction of the 

 gauge to 3ft. Gin. cripples the engine-power, or that, on the 

 other hand, the increase to 6ft. 3in. gives facilities for the use 

 of inside cylinders of larger diameter than can be used on the 

 standard gauge without altering the usual position of the valve- 

 chest, and introducing a consequent elaboration of the valve- 

 gear. 



Whilst therefore, in level country, light lines, whether of 

 standard or smaller gauges, may bring good results, the 

 crippling of the engine-power by reducing the gauge will often, 

 in the case of mountain roads, cause a great increase in con- 

 structive cost to obtain grades that can be worked with paying 

 loads by the lighter class of engines. 



Eakthwokk. 



Apart from the question of grades, it may be said, generally, 

 that the cost of the road depends not on the width between 

 the rails, but upon the weight of the engines, and the speed at 

 which the trains are to be driven. The margin of safety in 

 the width of the embankments depends on the weight to be 

 supported, and the stability required to stand without injury 

 the vibration of the trains. Whatever the weight of the engine, 

 the wider the platform by which that weight is distributed over 

 the top of the bank the more regular will be the settlement of 

 the earthwork, and the less the injury from vibration. Hence, 

 if a bank be narrow and weak, the evil will be increased, not 

 lessened, by reducing the width between the rails. 



The width of cuttings with sloping banks depends more 

 upon the width required for drainage, and for provision against 

 the track being blocked by slips, than upon the gauge ; but in 

 favourable ground the reduction in gauge will be followed by 

 a corresponding reduction in the cubic ^^contents of the exca- 



