52 Royal Society. 



velocities, and of the loss of force arising from increased back pres- 

 sure and the imperfect action of the steam. For this purpose he 

 institutes a comparison between the velocities actually acquired by 

 railway trains with those which the theory of accelerated motion 

 would have assigned ; and his experiments are made not only on 

 trains propelled by a locomotive engine, but also on those moving 

 on the atmospheric railway, which latter affords valuable results, 

 inasmuch as the tractive force is not subject to the losses at high 

 velocities necessarily incident to locomotive engines. A table is 

 given of the theoretical velocities resulting from calculation founded 

 on the dynamical law of constant accelerating forces, in the case of 

 trains of various weights, impelled by different, tractive forces, moving 

 from a state of rest ; and is followed by another table of the ob- 

 served velocities in Mr. Stephenson's experiment on the Dalkey 

 line ; the result of the comparison being that in a distance of one 

 mile and a quarter, the loss of velocity is about one-half of the ob- 

 served velocity. 



A series of experiments on locomotive lines is next related; but 

 the comparison is less satisfactory than in the former case, because 

 the tractive force cannot be so accurately estimated; it is however 

 sufficiently so to establish the fact, that the power lost by the loco- 

 motive engine below the. speed of thirty miles per hour is so small 

 as to be scarcely appreciable, and that the time and power which 

 are absorbed in putting a railway train in motion are almost entirely 

 required to overcome the inertia of the train, and do not arise 

 from any loss or imperfection of the engine. It appears, from these 

 experiments, that above one-fifth of the whole power exerted is con- 

 sumed in putting the train in motion at the observed velocity. The 

 author then enters into some general remarks on the effects arising 

 from this source of loss of power, and the practical application of 

 the knowledge thus obtained. In the atmospheric railway, he finds 

 that the tractive force of a fifteen-inch pipe is so small (being less 

 than half that of a locomotive engine), that the time of overcoming 

 the inertia must limit the amount of traffic which can be carried on 

 a single line, especially with numerous stations. When a great velo- 

 city is obtained, the tractive force of the locomotive is much re- 

 duced, and therefore a much greater velocity can be attained on an 

 atmospheric railway. 



The inquiries of the author into the amount of resistance exerted 

 by the air on railway trains lead him to the conclusion that in the 

 atmospheric railway the loss of tractive power of the piston from 

 friction, &c. is very inconsiderable ; and that the resistance of the 

 air is less than had been hitherto estimated, not exceeding, on an 

 average, ten pounds per ton on the average weight of trains. 



A tabular statement is then given of the results of the experi- 

 ments made by the British Association, for the purpose of com- 

 paring them with those obtained by the author from his own ob- 

 servations, and more particularly from his experiments on the Croy- 

 don Atmospheric Railway. The general conclusion which he draws 

 from this investigation is that the resistance of the air in a qui- 



