606 



this part of the spine, the spinal canal is enlarged laterally at the 

 centres of motion. The paper is illustrated by drawings of the parts 

 described. 



March 19, 1846. 



The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" Investigation of the Po^Yer consumed in overcoming the Inertia 

 of Railway Trains, and of the Resistance of the Air to the motion 

 of Railway Trains at high velocities." By P. W. Barlow, Esq., 

 F.R.S., MJ.C.E. 



The object of the author in this inquiry is to obtain a more cor- 

 rect knowledge than has hitherto been possessed of the resistances 

 which the air opposes to the motion of locomotive engines at great 

 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 

 ti^ains propelled by a locomotive engine, but also on those moving 

 on the atmospheric raihvay, 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 pow-er which 

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

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

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

 experiments, that above one-fifth of the whole powder 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 



