236 



KIGHTH EEPOET 1838. 



staked at intervals of 100 yards, and the 50|^ mile-post from 

 Birmingham M'as 55 yards beyond the l7th stake. The re- 

 mainder of the plane was divided by quarter-mile posts. In the 

 following table the times of passing the successive posts in each 

 experiment and their differences are given. In the column of 

 mean differences the mean time of traversing a hundred yards 

 is given, the means being taken at intervals as in the former 

 tables. 



In the first experiment there is a gradual retardation, which 

 continues until the train is stopped by the brake. At all the 

 velocities, therefore, which it attained, the resistance to its mo- 

 tion was greater than its gravity down the plane. 



In the second experiment, where a greater extent of the plane 

 is given for the motion, the retardation is also continued until 

 the train passes to the succeeding gradient. The average speed 

 of the train for the last quarter of a mile is 100 yards in 24* 1 

 seconds, or 12*4: feet per second, being at the rate of S^ miles 

 an hour. Hence we infer that the resistance to the train at tliis 

 speed vvas greater than its gravity down, 1 in 266, wliich is 

 equivalent to 8'5 lbs. per ton. The total resistance of this train 

 of 30 tons, was therefore greater than 255 lbs. at 8^ miles an 

 hour. 



