254 



REPORT — 1841. 



engine, Avhich on reaching the post No. 0, ceased to propel. The force of gra- 

 vitation afterwards accelerated the speed down the plane. An examination 

 of the respective rates of acceleration will give the means of determining the 

 resistances in each case. See Tables, Nos. VII. and VIII. 



Four Grand Junction Carriages = 20*45 tons. 



Six Grand Junction Carriages = 30*45 tons. 



We shall now examine the experiments made on the Grand Junction planes, 

 and then present a summary of the results of the whole series. A moderate 

 breeze blew directly down the plane during the course of the experiments. Its 

 effects could not be accurately estimated, but as the wind acted to favour the 

 descent of the train, the amount of resistance experienced and recorded must 

 be less than could have been obtained in a calm state of the atmosphere. The 

 error is on the right side for strengthening the force of the argument, which 

 maintains the existence of an opposing power far exceeding what hitherto it 

 had been supposed was encountered, and created as it were by the speed itself. 

 At no very distant period in the history of railways, calculations were adduced 

 before committeesof the Houses of Parliament, to prove the dangerous tendency 

 of permitting such gradients as 1 in 100 to be formed on any railway, and to 

 show what an enormous and fearful acceleration would take place in the mo- 

 tion of a train if allowed to descend such planes without control. Even a 

 plane of 1 in 177, it was supposed would demand a vigorous application of the 

 brakes to limit the velocity within due bounds. In the infancy of the system, 

 and the absence of extended experience, mistakes like these were natural. A 

 valuation of the friction of carriages had been frequently made by various in- 

 quirers with a considerable degree of accuracy. They however overlooked 

 in a great measure the influences brought into play by the rapidity of motion, 

 and erred in forming too early generalizations from data still imperfect, ap- 

 plying the same standard to weigh the opposing forces, whether the train were 

 proceeding at the speed of a steam-boat on the ocean, or winging its way 

 through air with the swiftness of an eagle's flight. 



The experiments described in this and the former Report show the fallacy 

 of erecting theories and establishing formulae on too slender a basis of facts. 

 In a department of science, whose principles and laws are not yet fully deve- 

 loped, it behoves us to proceed upon a plan of the most cautious and rigid 

 induction. Formulae derived from mere theoretical considerations are of little 



