264 REPORT — 1841. 



respondent with the increments of speed, but it now became more than pro- 

 bable that such resistance was in a gi'eat measui'e dependent upon the ^rewcra/ 

 volume of air displaced. The -weight of the displacing bodies in the instance 

 before us was the same, but their volumes were to each other in a somewhat 

 greater ratio than 2 to 1, and the effect is sufficiently remarkable. The 

 train of least volume ran -lOSO yards (or more than 2^ miles) further than 

 the train of gi'eatest volume, both trains being allowed to descend by gravity 

 from a state of rest from the same post on the Madeley Plane. This import- 

 ant fact appears to point out the path in which future investigations should 

 be conducted. 



The Committee have not had the opportunity of entering further upon it, 

 but they recommend future experimentalists to direct their attention espe- 

 cially to the effects of increasing and diminishing the bulk of the trains, the 

 weight remaining the same. Until more experiments of this nature have 

 been obtained, we cannot expect to arrive at a complete and satisfactory 

 theory of resistance. 



One plain and practical inference to be drawn from the fact of the resist- 

 ance being found to depend in a greater or less degree on the volume of air 

 displaced in connection with the rate of displacement, is, that the less the 

 space or bulk into which a given weight of train can be condensed, the less 

 does the resistance at a given rate of speed become, and consequently the 

 greater is the economy of moving po\ver. 



If the amount of resistance at present experienced at the ordinary rates of 

 travelling be susceptible of diminution, the saving will probably be effected 

 more by alteration in the bulk of the train than by attempting complicated 

 changes in the mechanical construction of the carriages with the view of 

 reducing the friction. 



For the ordinary purposes of railway transport, we cannot, indeed, antici- 

 pate any very material reduction in the space occupied by the different ve- 

 hicles, but we shall be Avarned of the consequences attending any attempt 

 at enlarging their dimensions without rendering them at the same time capa- 

 ble of carrying a proportionally greater load. Especially we shall guard 

 against the injurious consumption of moving power which may arise from 

 the provision of more accommodation than is absolutely wanted. When the 

 tide of traffic sets in one particular direction, it is impossible to avoid having 

 the trains travelling in the opposite direction encumbered with a useless load 

 of empty vehicles ; but under ordinary circumstances it would seem practica- 

 ble, by exercising due foresight, and by a judicious system of management, 

 to apportion the profitable and unprofitable parts of the load more correctly 

 and closely to each other. 



In estimating the amount of moving power expended in working a line of 

 railway, we have to consider, — 



1. The character of the line, or nature of its gradients. 



2. The weight as well as bulk of the train to be conveyed over it. 



3. The speed at which the load is required to be conveyed. 



If the resistance to each ton of load on a level railway could be repre- 

 sented by a constant quantity, at whatever speed the load were moved, it 

 would become an easy matter to calculate the resistance to be overcome on 

 any given line and length of railway, and to provide our power accordingly ; 

 for knowing the weight of the train, multiplying such weight by the coeffi- 

 cient of resistance, and this product by the length of road, we should at once 

 obtain the resistance upon an equal length of level railway, and afterwards 

 adding or subtracting, as the case might be, any increase or diminution of 

 resistance, arising from ascending or descending gradients, we should obtain 



