TRANSACTIONS OP SECTION J. 499 



reduction of stability, the bringing-down of the centre of gravity 

 of the engine, and consequently the reduction of the size 

 of the driving-wheels, and, as a necessary result, however 

 great the haulage-power of these engines, there is a serious 

 diminution of speed as compared with engines built for wider 

 gauges. 



On the other hand, the cost of light engines is but little 

 increased by building them on wude gauges, and the size of 

 the driving-wheels then enables them to develope speeds equal 

 to those of heavier engines. 



x\n engine with 6ft. driving-wheels will be propelled the 

 same distance as one with 3ft. wheels with only half the 

 number of piston-strokes, and, although piston-speed depends 

 on the length of the stroke as well as upon the number of the 

 revolutions of the driving-wheel per minute, this illustration 

 gives a clear idea of the causes which govern the relative speeds 

 of engines on the narrow and on wider gauges. 



Now let us consider how far the question of speed affects 

 the cost of the rolling-stock. 



Putting aside the question whether the day's work of an 

 engine is to be reckoned by the time under steam or by a 

 maximum of mileage run, and the consideration of the extent 

 to which the number of engines required to work a given 

 traffic is reduced by increasing the speed at which they run, 

 what is the effect of raising the ordmary narrow-gauge speed 

 of fifteen miles an hour to the ordinary broad-gauge speed of 

 thirty, with express speeds of forty and fifty, stoppages being, of 

 course, included in all cases ? 



Simply, so far as passenger traffic is concerned, that nearly 

 double the amount of mileage can be covered in a given time 

 with the same number of carriages, and the same number of 

 hours' wages paid to drivers, firemen, and guards. Broadly 

 speaking, the passenger-traffic on the broad gauge may be 

 carried on with little more than half the number of carriages 

 required on the narrow gauge, with a corresponding saving in 

 lengths of sidings and carriage-sheds — a matter of great im- 

 portance in metropolitan stations. 



A similar saving will result in the number of trucks, but 

 not nearly in the same proportion, as the time occupied in 

 loading and unloading is not affected by the speed of transit. 



Carriages. 



Next, how does the gauge affect the construction of car- 

 riages and trucks ? 



Narrow-gauge passenger-carriages with longitudinal seats 

 and end-doors are very convenient ; but, with the narrow 

 gauge, sleeping- and dining-cars cannot be made of sufficient 

 width without a dangerous overhang. 



