304 Mr POWER, ON THE PREVENTION OF THE 



had been adopted for some days previous. It appears also that the rate 

 at which the train was proceeding was nothing more than the usual 

 rate, which was well warranted by the sound state of the rail. Indeed, 

 no danger, or cause of danger, appears to have been suspected by any 

 person belonging to the establishment up to the moment the accident 

 commenced. 



The first engine was, indeed, described as top-heavy, having been 

 recently filled with water, but this was nothing more than must usually 

 occur under similar circumstances, that is to say, when a pilot engine is 

 first attached. 



We have, then, before us a train of carriages (including the large 

 six-wheeled engine, whose steam had previously been turned off), drawn 

 at a comparatively moderate rate by a four-wheeled engine in front, 

 and in the apparent absence of predisposing causes, we have to account 

 for the continued jumping motion, which was observed to take place 

 in the front engine upon the driver's turning off his steam. 



Now it occurred to me, that the motion described was exactly such 

 as would have resulted from a series of jolts or moderate impulses com- 

 municated at the back of the engine, provided they were communicated 

 at a point considerably lower than its centre of gravity ; and I pro- 

 pose to show, in the first place, how an impulse from behind com- 

 municated lower than the centre of gravity would cause the front engine 

 to lift up its fore wheels ; and secondly, to point out how, under the 

 circumstances of the case, a succession of such ascents of the fore wheels 

 might possibly have taken place. For, be it observed, the phenomenon to 

 be explained is not so much the final overthrow of the engine, as the pre- 

 ceding jumping motion, or series of jumps, which led to it; a single 

 jump might, no doubt, have been sufficient to cause the accident, but the 

 probability of danger arising from a single jump, would be incomparably 

 smaller than that which would arise from any cause which rendered 

 possible a continued series of them, such as was in fact observed to take 

 place on the present occasion. 



I shall demonstrate hereafter the following important proposition, 

 namely, that there exists at the back of a locomotive carriage of any 



