52 



THE CIVIL ENGINEER AND AllCMITECT'S JOURNAL. 



[!•' 



K ;< R u A a Y , 



for a considerable distance, and presuming that the engine should become 

 detached from the tender, its impetus would carry it far in advance; so 

 much so, that the train would fail in overtakin;; it. The engine would 

 proceed faster than the carriages. In order to show you the eli'ect of sud- 

 denly shutting oil' the steam, I was lately on an engine on the Bristol and 

 Gloucester Railway with Mr. Connell, the locomotive superintendent, the 

 Gauge Commissioners being in the train, when I desired a greater speed to 

 be put on, and then requested the steam to be turned olT suddenly. It was 

 done so, and not the slightest effect was produced. Again, on the (Jreat 

 Western Railway I was on an engine with Mr. Brunei — two tenders at- 

 tached and a goods'-train of 2,000 tons, with a speed of 30 miles an hour. 

 I desired Mr. Brunei, when they had to stop at a station, to sliut oil the 

 steam suddenly a minute before the breaks were applied. It was done 

 frequently, and not the least elfect felt. The tender did not crowd upon 

 the engine, and neither did the wagons crowd upon the tender. In short, 

 shutting oil' the steam produces no effect, unless the breaks are applied, 

 more especially in descending an inclnie of 1 in 20U. At the New Cross 

 incline, which is 1 in 100. the trains are always stopped by turning the 

 sleum ofT suddenly, and applying the breaks immediately, and if the cause 

 of the accident was really the shutting oil' the steam, accidents would be 

 constantly occurring at New Cross. Whenever there was a necessity for 

 such a step I should have no hesitation in adopting it. 



Coroner — Then, Sir, you quite disagree with Mr. Bidder's opinion as to 

 the cause of the accident.' 



General Pasley — I consider IMr. Bidder's opinion perfectly erroneous ; 

 at the same time I « ish to observe that INlr. Bidder is a gentleman of much 

 ability, but in this case I think he is much mistaken ; his opinion is con- 

 trary to the first principle of mechanics. Tlie dimensions of the engine are 

 19 ft. Gin. in length, without the foot-plates which the engine-driver and 

 occasionally the stoker stand upm, which gives about 2 feel more. The 

 distance from the centre of the front and hind wheels is 10 ft. 3 in., so that 

 the smoke-box is projecting befitre the fore wheels, anti the tire-box and 

 dome overhanging the hind wheels. In all engines, before Mr. Stephenson 

 look out his patent for the construction of the long-boiler engines, the hind 

 wheels are in the rear of the fire-box and dome, and consequently there is 

 nooverhanging dead weight at the rear of the wheels. W'lien I first saw 

 the engines I thought them very good in travelling at a moderate rate, but 

 1 now see no advantage in their construction or improvement. The fore 

 part of the boiler being so far from the tire-box, the tubes being so much 

 distant, the engines do not afford the power that was expected from them. 

 The engines of Sharp, Brothers, and Co., with moderate length boiler, 

 possess equal or greater power, and are free from danger. 

 Coroner — Are there any signal posts to denote gradients 

 General Pasley — After the first accident on the Eastern Counties 

 Railway, the Earl of Dalhousie .wrote to the board desiring that all 

 the inclines should be marked out with posts, which had been done 

 to guide engine-drivers ; for at the accident at Liltlebiiry, on that line, the 

 superintendent of the locomotive departuifut, who was on the engine, and 

 the driver, were really descending a gradient without knowing it. 



Coroner — Mr. Bidder has told us that on gradients of 1 in 200, engines 

 are in the habit of travelling at the greatest velocity? 



General Pasley — Then that is contrary to my general experience. I 

 never travelled an incline but that the steam hnd been partially or perfectly 

 shut off. It is a general rule to shut it off on going down an incline. I do 

 not think that on a gradient of 1 in 200, engines are in the habit of running 

 at the greatest possible velocity. 



Coroner — Then we perfectly understand you to say, that shutting off 

 steam in descending a gradient would not cause an engine to stop ? 



General Pasley — Certainly, if the breaks were not applied. If the de- 

 cline is 20 miles in lengtii, it will not stop until it comes to a level. It is 

 the source of gravity. Its momentum forces it along. 



The learned Coroner proceeded to sum up the evidence, anti after com- 

 menting on the principal facts as related to tlie unfortunate occurrence, re- 

 marked upon the wide contrast of opinion enleitaiued by .Major-Geneial 

 Pasley and Mr. Bidder. It was for liic jury to determine, knowing well 

 that they would so decide as would ensure the public evei;y safety. 



The verdict was " Accidental death, caused by the imprudent conduct 

 of the engine driver in going at an excessive speed." 



General Hasley, on his return to town by ilie last train, rode on the en- 

 gine of the Eastern Counties („"oinpdny, one of the same description as those 

 that ran off the rails at Liltlebury and U'aterbeach, built by Stothart, 

 Slaughter, and Co., in order to test ils capabilities 'I'he speed ou one por- 

 tion of the line between Bishop's Siortford and Sti-aiford was for a short 

 time upwards of 4.'> miles an hour, anil the engine rode very steady ; and 

 in two or three instances, on nearing a station, he directed the engiue-driver 

 to turn the steam off suddenly, full a minute before the breaks were put 

 down, and not the slightest effect was produced. 



The reply of Mr. Bidder appears in the form of an advertisement, pub- 

 lished in the Times, from which we make the following extracts: — • 



"The substance of the evidence nhich I gave was to the effect, that by 

 the sudden shuttini; off of the steam of the engine, the carriages were no 

 longer drawn by the engine, but that the engine was propelled by the car- 

 riages, and that this, in combination with other circumstances which (as I 

 then stated) might not occur once in a thousand times, had, on this occa- 

 sion, the effect of forcing the engine off the line. 



'• The grounds upon which I formed tliis opinion are based upon what I 

 must still believe to be a well-established law of mechanics — viz., that in 

 any system of bodies moving together, if there be no resistance, or if the 



resistance of each body be in the like ratio to its weight, when the motive 

 power ceases to act upon them, these bodies will exert no influence upon 

 each other in any direction, but if the resistance to the motion of the 

 bodies in front be greater than that which is required to sustain the motion 

 of those which are liehiud. the retardation of the former will be more rapid 

 than that of the latter, and will be impelled by them, and rice versa. 



"Applying this to the case of a railway train in motion, we have this fact 

 for our guidance — that an engine requires from 7 to 12 lb. per ton more to 

 sustain its motion than the cairiages — it must inevitably follow, that the 

 effect of suddenly shutting off the steam causes the carriages to overtake and 

 impel the engine forward, as staled by me in my evidence." 



It certainly must be conceded that assuming with Mr. Bidder, the re- 

 sistance to motion to be 7 to 12 lb. per ton more for an engine than for car- 

 riages, the carriages will exert a pressure against the engine when the 

 steam is suddenly cut off. But the misapprehension on which General 

 Pasley grounded his censure of Mr. Bidder appears to be this — that he 

 presumed Mr. Bidder's notion to be that the carriages acted on the engine 

 not by a continuous pressure, but by impact or collision. There is no ground 

 however for supjiosing that Mr. Bidder entertained this idea. At the same 

 time while defending him from the charge of having erred in the first prin- 

 ciples of mechanics, we do not hesitate to deny the possibility of the acci- 

 dent having arisen from the causes assigned by him. 



It appears from the very careful and elaborate experiments of M. de 

 Paiiibour, that the friction of an engine when not drawing a train (the case 

 here supposed) is about 14 lb. per ton. The friction of carriages is 61b. 

 per ton. This gives an excess of 8 lb. per ton for the friction of the engine. 

 But from this must be deducted the resistance of the air, a most important 

 item in considering high velocities. The resistance of air on the carriages is 

 much greater than on the engine in proportion to the weight of each. We 

 should be quite safe in supposing that at velocities ranging from 30 to 50 

 miles an hour, the resistance from this cause is 3 or 4 lb. greater per ton 

 on the carriages than on the engine. So that on the whole we may safely 

 conclude that when the engine and train are disconnected at a high velu 

 city, the steam being cut off at the same time, the excess of resistance on 

 the engine is certainly not more than 5 lb. per ton. 



Now we shall have no difficulty whatever in showing that the pressure 

 which the carriages will exert on the engine under these circumstances 

 is no greater ihan that which could be easily exerted by a boy 12 or 14 

 years old. By the very simplest mathematics it may be demonstrated that 

 the pressure is equal to 5 times the product of the number of tons which 

 the train and engine weigh respectively, divided by the sum of those num- 

 bers.* For instance if we suppose the weight of the train 40, and of the 

 engine 10 tons, the product of tho.se two numbers (400) being divided by 

 their sum (.'jO) gives 8, which multiplied by 5 gives 40 lb fur the pressure 

 on the engine. Again, take the weight of the train at 60 tons, and of the 

 engine at 12 tons, 12 x CO is 720 and 12 + 00 is 72 ; dividing 720 by 72, 

 and then multiplying by 5 as before, we ^et 501b. for the pressure on the 

 engine. 



It must be carefully uoled that the pressure here calculated represents 

 the wlwle effect of the train on the engine. There is nothing like impact 

 or collision because the velocities of both engine and carriages are in- 

 itially the same, Hud ure grail ualhj retarded. 



Now it would be perfectly ludicrous to imagine that a pressure of 40 or 

 501b. would injure au engine or force it oU' the line. Taking the weight 

 which a man can usually raise at 2001b. (no very high estimate) we have 

 for the pressure in question one-fifth to one-fourth of tlic average of human 

 strength. Even if we take Mr. Bidder's own account and assume the 

 excess of resistance to the engine over that to the train at 7 to 12 lb. per 

 ton, the case is made very little better, for even then the pressure is not 

 nearly so great as that which could be exerted by one man. 



* Let BI be ttie number of tons which the train weighs, F the resistance per ton to ilt 

 P th'.- ii)>ilual pressure betwreii tile train and engine; then nieasiinng Ihe accelerating 

 lorce t'runi the time ul discuutiecting the two, in the direction of uiotioii, we have 



U- — =-MF-P 



d t- 



for the motion of the carriages. For the motion of the engine we have, putting M' lor 

 the ouLQbtT of tuns, uiii'l K' lur resistance per ton, 



M'— i^=_M'F' + P 

 dt' 



P here changing its sign. Equating the values of the diSferentiat (which we may cleirly 

 do since the carriages and engine an supposed to continue mtviog al the saioe vtlocit;) 

 we get the pressure P equal lo 



M M' 



M + M' 



(F-F). 



