92 C. O. BUKGHE. 



Sharp curves must be avoided in steep rack inclines, not only 

 for the reason applying to ordinary lines, that the resistances due 

 to these should not, if possible, be coincident, but for others due 

 to the working of the system itself. Owing to the danger arising 

 from possible failure of drawbars, the rack engine is usually placed 

 at the lower end of the train, and in ascending, is therefore push- 

 ing its load. The limiting safe stress on drawbars for instance in 

 New South Wales railways is 25,000 lbs. which on a grade of 1 in 

 12 \ would be the strain produced, together with train friction, by 

 a load of about 130 tons only, so that accidental overloading 

 might conceivably occur, and cause a breakaway, if the engine 

 were in front. Now sharp curves are always likely to cause 

 derailment of a train if it is impelled from the rear, as it is obvious 

 that if there is any tendency on the part of any vehicle to mount 

 the rail, which is more likely on curves, this is intensified if pushed, 

 and counteracted if pulled by an engine still on the rails. 



The serious nature of an accident through the breaking of a 

 drawbar in a train which is being pulled up such a severe grade 

 as the provision of a rack implies, is evident, as there would be 

 certain to be some small interval of time between the fracture of 

 the bar and the full application of the brakes, during which the 

 speed on such a grade would probably have attained a dangerous 

 excess. 



The drawback of limiting the application of the rack to lines 

 of easy curvature is a serious one, as it is just in the mountainous 

 regions where such a contrivance is required that sharp curves are 

 wanted to lessen works and to provide length, so as to moderate 

 excessive grading. The Abt Company strongly recommend a 

 minimum radius of 9 chains for 1 in 12 J grade on our standard 

 gauge, and this is the limit on the Abt standard gauge line 

 Eisenerz to Vordenburg in Styria, where the grade is 1 in 14*7. 

 However on the Yisp Zermat 1 in 8 line in Switzerland, and the 

 Nilgiri in India, both on the metre gauge, push-up engines are 

 used on 5 chain curves, which is much smaller in proportion than 

 9 chains on the 4 ft. 8 J in. gauge, and there are other similar cases. 



