1835.] the Advancement of Science. 221 



is, supposing the rail-road to be level. Suppose a rail- road 

 rising 1 foot in 250, resistance to traction then proceeds 

 from two causes, the resistance on the level, as already ex- 

 plained, and the resistance offered from the actual declivity. 

 The resistance to be overcome on the level is equivalent to 

 nine pounds per ton, and on the road ascending 1 foot in 

 250, it vv^ould be eighteen pounds per ton, and thus it is 

 seen, that in the latter case, the drawing power must exert 

 twice the force necessary on the level. If the road rose 2 

 feet in 250, the drawing force would be twenty-seven pounds 

 to the ton. This view of the subject is confined to ascents, 

 but it should not be forgotten, that when a rail-road is 

 worked, the transit is from one end to the other. It is 

 necessary, in estimating the merits of rail-roads to consider 

 their action downwards as well as upwards. In coming 

 down a steep, no force is required to impel an engine, and 

 the gravity restores that force in going down which it has 

 robbed from it in the ascent. You have to provide, in an 

 ascent of 1 foot in 250, for a resistance of eighteen pounds 

 to a ton, but in descending no force is required. Kit was 

 desired to strike an average between the ascent and descent, 

 the road would present a surface which would be equivalent 

 to a level. This point, respecting ascent and descent, struck 

 the House of Lords, before which he gave this opinion, as a 

 paradox, but it was one only in sound and not in reality. 

 Dr. Lardner remarked, that these observations referred to 

 ascents not more steep than 1 foot in 250 ; but supposing 

 the rise to be 3 feet in 250, and where the strain would be. 

 consequently, thirty-six pounds in each ton, would gravity 

 give this back in the descent ? It was true, that no power 

 was required in descending, but while only nine pounds 

 were gained in the descent, twenty-seven pounds were lost 

 in the ascent. Beside the loss of power, there was also the 

 danger resulting from the too great velocity occasioned by 

 sudden descents. In one of the lines of rail- way, for which 

 a bill had been applied to the House of Lords, there was a 

 slope of 1 foot in 106 in a descent of two miles and a-half 

 long, and the velocity given to an engine on arriving at the 

 foot of the slope, could not amount to less than 70 miles art 

 hour. To mitigate defects arising from these abrupt de- 

 scents, breaks were applied, but not always with success. 



