

136 IMPORTANCE OF FLAT GRADIENTS. CHAP. VIII. 



on the subject were neither believed in nor acted upon 

 by practical engineers. 



He ascertained that the resistances to traction were 

 mainly three ; the first being upon the axles of the 

 carriages, the second, or rolling resistance, being between 

 the circumference of the wheel and the surface of the 

 rail, and the third being the resistance of gravity. The 

 amount of friction and gravity he could accurately 

 ascertain ; but the rolling resistance was a matter of 

 greater difficulty, being- subject to much variation. But 

 e satisfied himself that it was so great when the surface 

 presented to the wheel was of a rough character, that 

 the idea of working steam carriages economically on com- 

 mon roads was dismissed by him as entirely out of the 

 question. Taking it as 10 Ibs. to a ton weight on a 

 level railway, it became obvious to him that so small a 

 rise as 1 in 100 would diminish the useful effort of a 

 locomotive by upwards of 50 per cent. This was de- 

 monstrated by repeated experiments, and the important 

 fact, thus rooted in his mind, was never lost sight of 

 in the course of his future railway career. 



It was owing in a great measure to these painstaking 

 experiments that he early became convinced of the 

 vital importance, in an economical point of view, of 

 reducing the country through which a railway was 

 intended to pass as nearly as possible to a level. Where, 

 as in the first coal railways of Northumberland and Dur- 

 ham, the load was nearly all one way, that is, from the 

 colliery to the shipping-place, it was an advantage to 

 have an inclination in that direction. The strain on the 

 powers of the locomotive was thus diminished, and it was 

 an easy matter for it to haul the empty waggons back to 

 the colliery up even a pretty steep incline. But when the 

 loads were both ways, it was obvious to him that the rail- 

 road must be constructed as nearly as possible on a level. 1 



1 This subject will be found further 



moir on the Invention of the Railway 



discussed in Robert Stephenson's ' Me- Locomotive,' appended to this volume. 



