210 EIGHTH REPORT — 1838. 



This is just the effect which the resistance of the air would 

 produce. If the velocity were the same in both experiments, 

 that part of the total resistance due to the air would be the same, 

 because the same wagons being used in each case, the same 

 surfaces were exposed to the air. In that case, therefore, the 

 same amount of atmospheric resistance being divided amongst 

 a less number of tons, there would necessarily be a greater re- 

 sistance per ton in the second experiment, and the gross re- 

 sistance of the train would be diminished in a less proportion 

 than the load. 



But it is evident that the mean velocity must have been less 

 with the lesser than with the greater load, because a less amount 

 of atmospheric resistance would be sufficient, combined with 

 friction, to balance the diminished effect of gravitation. M. de 

 Pambour, however, did not observe, or at least has not recorded, 

 the time which the train took in any case to move down the 

 plane, or to come to rest, and has not, therefore, supplied any 

 data by which the mean speed can be computed. 



If it be admitted that the resistance due to friction is inde- 

 pendent of the velocity, it will follow that the difference between 

 the resistance per ton in the one experiment and the other must 

 be altogether ascribed to the air. Now, if A express the whole 

 resistance due to the air in the first experiment, and A' in the 

 second, we shall therefore have 



25-58 31-31 



equal to the difference of the resistance per ton in the one case 

 and the other. Hence we shall have 



^ ^ = 9-17 - 8-69 = 0-48. 



25-58 



25-58 31-31 

 Let A' = A — A . Hence we obtain 



^(2^-3r3T) = «'^^ + 



Whence we find 



A = 67 + 5-5 A. 



In the absence of the necessary data for determining A , we can 

 only infer from this that A > G*]. Now let/' be the resistance 

 due to friction, properly so called, in lbs. per ton. We have 

 then 



31-31/ + A = 272, 

 .•.31-31/ = 272 -A. 



