1 68 Railway Development. [April, 



As such tramways must necessarily follow the surface of 

 the ground to a great extent, avoiding heavy earth-works, it 

 is worth while to consider what really are the limits of 

 gradient. 



If we take two pieces of clean iron and lay one on the 

 other, and gradually lift one end of the lower one till the 

 superincumbent piece begins to slide, we shall find that 

 this sliding takes place at a slope somewhere between I in 

 4 and i in 6 ; this, therefore, is the ultimate co-efficient of 

 friction, and varies according to the condition of the surfaces 

 in contact of the metal. 



Let the uppermost piece of iron be taken to represent the 

 engine, the lower one the rail, the wheels of this engine 

 being locked and prevented from turning, it will just stand 

 at i in 4 to i in 6 ; therefore, if the wheels are caused to 

 revolve, it can just climb this gradient under the most 

 favourable circumstances. 



But rain, fogs, and sleet prevent this result from being 

 arrived at in practice, and engineers seem to agree that i in 

 io is the most that can be climbed in all weathers with 

 certainty ; therefore, taking this as the datum, up half that 

 gradient, or I in 20, the engine can take a load behind it 

 equal to its own weight, and up 1 in 30 twice that weight. 



Therefore a 10-ton engine can haul 20 tons up 1 in 30, or 

 two loaded wagons, of say 5 tons each, carrying 10 tons of 

 paying load : the non-paying load being 10 tons. 



It would appear, therefore, that 1 in 30 is about the 

 steepest incline which should be adopted for any length ; 

 this gives a rise of 176 feet in a -mile, and practically 

 commands most countries. 



Near Aberdare Junction, on the Taff Vale Railway, ordi- 

 nary locomotives can be seen regularly working up 1 in 18, 

 ■ — which is a practical proof of the foregoing statements, — 

 they take loads behind them of 45 tons. 



Between Manchester and Oldham, where the traffic is 

 enormous, the gradients reach as high as 1 in 27 — and 

 ordinary locomotives with coupled wheels climb this, with 

 loads behind them of 60 to 80 tons regularly. 



These instances merely show extreme cases neither to be 

 copied nor commended, but where occasion requires to be 

 employed sparingly as precedents. 



If 1 in 30 be the worst place on the tramroad, a 10-ton 

 engine could nevertheless haul two cars containing over 

 150 passengers up it ; this would be more than would be 

 requisite in an agricultural district. 



Having roughly defined the limit of gradient, let us 



