DISASTROUS EFFECTS OF COLLISION ON RAILWAYS. 317 



a quantity, which it is desirable to render as small as possible, in order 

 to ensure safety to the engine or carriage under ordinary circumstances. 



It has lately been the subject of discussion, whether, by increasing 

 the distance between the bearings, the proportionate increase of the 

 linear ascent of the wheel, due to a given angular rotation, would not 

 increase the danger of running off the rail. 



The preceding result shows, that no such danger is to be feared, 

 but that, on the contrary, the increased linear ascent of the wheel, 

 due to the greater length of revolving radius, is far more than com- 

 pensated by the diminution of the angular velocity itself; and, as 

 regards the comparative safety of four-wheeled and six-wheeled engines, 

 it shows a decided advantage in favour of the latter : — 



1st, because they admit more readily of the diminution of h by 

 placing the centre of gravity lower. 



2nd, on account of their greater mass. 



3rd, on account of the greater distance between their centre of 

 gravity and the axles of the fore and hind wheels. 



4th, on account of the increased value of k, the radius of gyration. 



P. S. Since the above communication was read, an equally dis- 

 tressing event has taken place on the Great Western Railway, which 

 affords a striking illustration of the importance of these principles. 

 The persons who travelled upon or next to the luggage trucks were 

 the unfortunate victims on this occasion, and the fatal consequences ap- 

 pear to have arisen from the rolling of the trucks one over another, on 

 the train being unexpectedly stopped by a fall of earth lying upon 

 the railway. Had the buffers been placed at the proper horizontal 

 level, this rolling motion could not have taken place, and the loss of 

 human life might have been prevented. 



J. POWER. 



Trinity Hall, 

 April 12, 1842. 



Vol. VII. Part III. M m 



