ttAILWAY CONSTANTS. 



209 



along the gradient at the foot of the plane until they had traversed 

 9933 feet and had attained a level 38*55 feet below the point 

 from which they started. Hence, by the formulae already given, 



O Q C C 1 



the ratio of the friction to the load would be — = , beina: 



993300 258 ^ 



at the rate of 8'69 lbs. per ton of the gross load. 



By throwing off a quantity of the bricks the load was then 



reduced to 25*58 tons, and the experiment was repeated in the 



same manner, when the proportion of the resistance to the load 



was found to be — — or 9' 17 lbs. per ton. 

 244 *^ 



Three loaded wagons and an empty one were next allowed 



to run separately down the plane, and the following were the 



results. 



Without pursuing the experiments of M. de Pambour further, 

 it will be easily perceived that the atmosphere must have exei*- 

 cised upon them an influence much greater than he suspected, 

 and certainly greater than he has taken any account of in the 

 computations which he has founded on them. 



When the five wagons were chai'ged with a load amounting 

 to 31*31 tons gross, the resistance computed by the formula 

 (18.) was 8*69 lbs. per ton, and the total resistance was conse- 

 quently 272 lbs. When the gross load of the same wagons was 

 reduced to 25*58 tons, the resistance per ton, computed in the 

 same way, was 9*17 lbs., and the total resistance was 235 lbs. 



If the resistance were, like friction, proportional only to the 

 load, the resistance ^^er ton would have been the same in both 

 cases. But we find, on the contrary, that by diminishing the 

 gross load, the gross resistance is not diminished in so great a 

 proportion and the resistance per ton is increased*. 



• All the experiments which have been made to develope the laws of friction, 

 go to prove that, except in extreme cases, friction bears an invariable ratio to 

 the pressrue on the rubbing surfaces. When pressures, however, bearing a 

 very high ratio to one another are compared, the corresponding quantities of 

 fiiction are not found to be in this ratio, the friction corresponding to the greater 

 pressure bearing a ratio to that corresponding to the lesser pressure, less than 

 that of the pressures. This exception to the law of the constant ratio between 

 the friction and pressure has, however, no application in a case like the above. 



