Mr Adamson on Rail-Roads. 27 



obliged to have at one time, on a long line of road, no more 

 than that quantity of goods which the ropes or chains were cal- 

 culated to bear, while no other power could be employed on the 

 same line to remedy its failure or add to its capabilities. The 

 great and continual expence of renewing the exposed parts of 

 the machinery, in addition to these inconveniences, ought to be a 

 good reason for preferring even very expensive excavations to 

 this method of avoiding them. 



We could bring the fixed engine and the locomotive engine 

 more directly into comparison, if we could tell exactly the loss 

 of effect incident to each, in moving a given weight over a cer- 

 tain space. Whenever the friction of the rope or chain and its 

 rollers becomes the same proportional part of the load, as the loco- 

 motive engine''s friction is of its load, we may consider this waste 

 of power as equal. Mr Wood's experiments on inclined planes 

 afford us the means of approximating to a decision on this point, 

 though we must regret that the instances of the kind required 

 are too few, and too little varied, to lead us to certainty. If we 

 compare Nos. 14. and 15. of these experiments, we find that 

 the friction of a rope of a certain length, is represented in these 

 two cases by the numbers 239 tb. and 250 lb., of which the dif- 

 ference is 11 lb. Now, this rope was, at the upper end of the 

 plane, bent round a large fixed pulley or friction- wheel, the re- 

 sistance to the revolution of which, independent of the friction 

 produced by its own weight, we may assume as increasing in 

 proportion to the tension of the rope ; but from the manner in 

 which the rope acts on the other friction rollers, the retardation 

 caused by them may safely be assumed as constant. By exam- 

 ining the details of the experiments, we find that the tension of 

 the rope, in the 15th experiment, was greater than it was in 



the 14th, in the proportion of 1 -f -—- : 1. This determines 



what fractional part of the friction of the large wheel, the dif- 

 ference of 11 K). will amount to; and we wiU thus have 

 11 X 5.27, or 58 ft), as the resistance presented by the large 

 wheel with the lighter load. The friction of the wheel caused 

 by its own weight, will, by Mr Wood's rules, amount to 14 ft)., 

 and thus 72 ft) will be the total friction of this part of the mar- 

 chinery ; if this be subtracted from the total resistance of the 



