RAILWAY CONSTRUCTION. 47 



inclines, as well as applying the brakes on the ordinary and 

 extra brake-vans. The sprag is a piece of wood, circular in 

 section, about 2 feet 6 inches long, and 5 to 6 inches thick in the 

 middle, tapering off to about 2 inches thick at the ends. When 

 the waggon-wheel is just beginning to move, the sprag is inserted 

 between the spokes, and being caught against the waggon frame- 

 work, the wheel is held fast, and being unable to revolve, remains 

 fixed, and acts like a skid upon the rails. The skidding of the 

 wheels upon the rails wears flat places on the wheel tyres, and 

 it is needless to mention that the practice is only resorted to in 

 very extreme cases. Although a very primitive means for 

 checking the speed of a descending train, or for maintaining 

 vehicles stationary on an incline, there have been many instances 

 where lives have been saved and accidents prevented by the 

 prompt use of a few sprags. Solid or close wheels cannot be 

 spragged, only wheels which have spokes or openings, and for 

 this reason alone it would be very desirable that in every pas- 

 senger and goods train there should be some spoke or open 

 wheels which could be spragged as a last resource, in the event 

 of a sudden emergency of brakes failing or train becoming 

 divided on an incline. 



On ascending gradients there is always the risk of a coupling 

 breaking, and the train becoming divided. If the detached 

 portion left behind be provided with ample brake-power, 

 hand-brakes, or otherwise, no harm may take place beyond a 

 little delay ; but if the brake-power be insufficient or defective, 

 and if all the wheels are solid wheels incapable of admitting 

 a few timely sprags, then the vehicles cannot be held, but 

 must slide back, and running unchecked would soon attain 

 such a velocity as would cause them either to leave the 

 rails or dash into another train standing at the last station. 

 Many lamentable accidents have taken place arising from por- 

 tions of trains breaking away and running back, and the sad 

 experience of those casualties should call forth every effort to 

 avert a recurrence in the future. It may not always be possible 

 to detect a hidden flaw in a coupling, or a defect in the brake- 

 gearing until the actual failure occurs ; but it is quite possible 

 to guard against disastrous results from such failure, by pro- 

 viding means to hold the vehicles, and prevent them sliding back. 



For some years the writer had the entire charge of an im- 

 portant railway abroad on which the gradients were very 



