222 Proceedings of the British Association for [Sept. 



The break is a piece of wood, pressed against the tire of the 

 wheel by a lever, and if it acts with full effect it ought to 

 prevent acceleration. He had seen several cases in which 

 it had totally failed, and one instance, which occurred he 

 would detail. At one of the slopes between Manchester 

 and Liverpool, he was descending with a loaded train of 

 150 tons. The operative engineer, whether through a de- 

 sire of displaying the engine's movements, or through 

 neglect, forget to apply the break at the commencement 

 of the slope ; when half-way down, the velocity became so 

 great, that he requested the breaks to be applied, but on 

 doing so, they were instantly burned. The train went down 

 at a tremendous speed, although the supply of steam had 

 been cut off. When the train had been stopped it was found 

 that the wheels of one of the waggons which revolved with 

 the axis had been broken, and yet notwithstanding this 

 accidental drag, the speed amounted to at least fifty miles. 

 It was objectionable to have any slope exceeding 1 in 250, 

 for when the excessive natural powers of gravitation were 

 resorted to, control over its movements was impossible. 

 The conclusion to be arrived at, although it appears para- 

 doxical is that you may construct two rail-roads, say of 100 

 miles in length, one level, the other going over mountains, 

 and yet the two rail- roads may be worked by the same me- 

 chanical power. Suppose in the one you ascend 1 in 250, 

 and descend in the same ratio, a pull of eighteen pounds to 

 the ton is required only fifty miles, and on the other half 

 you descend by inertion. On the level road a pull of nine 

 pounds to the ton is required, from the entire distance of 

 miles, and thus the extent of exertion is equalized. It was 

 not, however, to be forgotten, that they should have a re- 

 gard to the power used. If the power to be used was that 

 of animals, then it might happen that the hilly road would 

 be better than the level, for nothing was better understood 

 than that a dead and unvarying pull upon the same set of 

 muscles, would have the effect of causing the labour to be 

 more severe, while a varying pull would alternately give 

 quiescence and exercise to the muscles. If the line was so 

 disposed as to throw the whole ascent in one pots, the ad- 

 vantage would be gained of having the rest of the road 

 nearly level. But the cost of attaining this advantage 



