256 REPORT — 1841. 



The times of passing from No. 30 to No. 54 posts, 2400 yards, were re- 

 spectivelj^ 



4 min. 8'0 seconds = 19"7 miles per hour. 

 4 . . . 5-75 ... = 19-9 ... 



4 . . . 20-50 ... = 18-9 

 The mean of the whole is 1 9*5 miles per hour. 



The force of gravity on the plane being expressed by ^^j, 8*45 lbs. per ton 

 was the mean resistance encountered by the train of eight carriages, when moving 

 at the mean velocity ofl9'5 miles per /lour. 



The train afterwards passed on to a plane of 1 in 330, but suffered throughout 

 a gradual retardation, showing that the resistance exceeded the gravitating 

 force on this plane. Were it deemed necessary a computation could readily 

 be made of the resistance at still slower speeds from the observed rate of re- 

 tardation, but this has already been determined from the Sutton experiments, 

 which, from the absence of any disturbing effects produced by wind, are more 

 to be depended upon. 



The trains of four carriages next require our attention. The fact of so 

 slight an acceleration as that from 23 to 25 miles per hour, having been pro- 

 duced during the descent of a plane more than 5000 yards in length, was suf- 

 ficiently remarkable, and demanded an accurate verification. It was deter- 

 mined accordingly to make a sort of experimentum crucis, by dismissing the 

 train from the head of the plane at a velocity considerably exceeding the 

 maximum hitherto obtamed during any portion of the descent, and to note 

 whether, instead of further acceleration, an actual retardation would not take 

 place. The event turned out as had been anticipated. 



The four carriages were dismissed over the top at 40 miles per hour ; their 

 speed diminished ; when half way down the plane it was reduced to 30 miles 

 per hour ; and by the time they reached the foot it did not exceed 25"17 miles 

 per hour. See Table, No. XII. 



The plane, it became evident, was too short to allow the train to acquire the 

 uniform velocity due to the resistance, otherwise, in all probability, the speed 

 would have been further lessened. 



The remaining four carriages, composing a train of equal weight with the 

 former, were now dismissed at 32*73 miles per hour. They were retarded to 

 22*72 miles per hour, and then continued uniform to the foot, over a space 

 of 1600 yards. The time occupied in traversing the last 1600 yards was 2' 

 23" = 22*8 miles per hour. 12*65 lbs. per ton was therefore the mean resist- 

 ance encountered by this train of four carriages, when moving at the mean ve- 

 locity of22-S miles per hour.' 



At the top of the 1 in 265 plane the speed of the first set of four carriages 

 was 25*17 miles per hour. This continued to decrease for 3400 yards, after 

 which the motion became uniform at 19*2 miles per hour, indicating a resist- 

 ance of 8*45 lbs. per ton. 



The wind, which up to the time of the last experiment had blown in a di- 

 rection to favour the motion of the trains down the plane, now veered round 

 to the westward and fell on the sides of the carriages, tending to press the 

 flanges of the wheel against the rails. This new source of resistance was soon 

 rendered evident by the sluggish motion of the second train of four carriages 

 in the latter part of its course (Table XIII.) ; also by that of a train of six 

 carriages (Table XIV.), which afterwards descended ; and lastly, by repeating 

 the experiments with the entire train of eight carriages (Table XV.). 



The Time Tables are given in the App. (see Tabs. XIII. XIV. XV.), but we 



