I8-J5. 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



341 



thnse used nn tlie long lines in England, with the exception of the Great 

 Western — {liergin.) 



S/irirl Lines. — On short lines where tlie traftij is very large, when the de- 

 jir lin's of trains are very numeroiH, ami 'vlicre there is no intermediate 

 ; ;.[•.]] ■ ti) accommodate, the atmospheric would be a very convenient arrange- 



I'.. It would not he more economical than the lilackwall, and not so 



convenient where there is intermediate trallic — (Sfr/ihrnsoJi.) 



The atmospheric system is particularly applicaljle to sliort lines with a 

 large number of passengers — (Cubitl.) 



Siilinr/s. — At the sidings and points carriages would he equally as liable to 

 get olTthe rails on the atmospheric as on locomotive lines; tliere is nothing 

 more to hold them — (Stephenson.) 



Slips. — Most of the slips on railways are caused hy the vibrations of the 

 trains, which is principally due to ibe locomotive. Slips of emhanknifnls 

 will t)e less likely to occur on an atmospheric than on a locomotive line. In 

 the event of slips the pipe could be easily replaced. Apart from other eon. 

 dilions. a slip is more likely to interrupt traffic upon a single line than upon 

 a double line — (Hninel.) 



Sou/A Devon Itailuay. — The South Devon railway, a line of 52 miles, is 

 being executed on tlie atmospheric principle ; 20 miles of the South Devon 

 line will be opened in July — (Samuila.) 



About 20 miles of the Exeter and I'lymouth line will be ready to receive 

 the atmospheric apparatus in June or July. The South Devon line has been 

 laid down entirely for a single line of rails, which makes peculiar arrange- 

 ments necessary at the stations — {Brunei.) 



S/ieed attainable on the Atmospheric Principle. — Means of varying the 

 power of the engine and the speed of the trains by working the tube to a 

 higher or lower degree of exhaustion ; illustrations of tliis power — (Sani^da.) 



" Uesiiles adopting as we do in extreme cases a varied size of tubes, we 

 have means of varying our power very considerably, hy working to a higher 

 or to a lower rlegree of exhaustion. We carry this to such an extent, with- 

 out varying the size of the tube, that on the Dalkey line it is a very common 

 practice for us to run with trains weighing only 16 tons ; and we have with 

 the same apparatus run with trains of 73 tons up the incline, which is an 

 average of 1 in 11."). We have the means of regulating that by regulating 

 the period at which the steam-engine shall start before the load ; that is to 

 say, if we have a very heavy load, and we wished to work with a vacuum of 

 20 inches upon the piston, we should start the engine sufficiently in advance 

 of the train ^it would be a matter of about four or five minutes) to obtain 

 that vacuum before the train arrived at the section at which it was to be 

 propelled hy the engine stationed in advance of it : and if on the other hand 

 we were starting a light load, we shouhl start the engine a proportionably 

 less time in advance of the train. This will he regulated by means of the 

 electric telegraph, which is fixed along the line, and which affords a means 

 of communication to every engineman of what vacuum will be required for 

 the ordinary tratlic of the day." 



AH trains would be carried at the same velocity, because the power would 

 be adjusted to the load — {Saniuda.) 



" Under ordinary circumstances, all trains would pass at the same velocity : 

 ■ heavy train would have an increased vai-uuni produced for it. Your pro- 

 position is to carry all trains at the same velocity .' — Yes; I should observe, 

 we do not contemplate carrying those immense luggage trains which they 

 carry on the locomotive plan; on the locomotive plan it is desirable that 

 they should carry them ; because they interfere with the passenger traffic, 

 therefore they go very slowly, they stop at the sidings, and they remain there 

 for the quick trains to pass them, and they often lemain a considerable time. 

 We propose to snbrlivide the loads so as to keep our trains, generally si>eak- 

 ing, of such a weight tliat we should he alile to send all our trains at the 

 greatest spe^d, and that would be one of the greatest advantages in point of 

 •eeuriy which we should have; we should have a continuous chain of trains 

 running on all at equal speeds, and not at variable speeds, as in the locomo- 

 tive sysem, in which one train is always approaching to overtake the pre- 

 ceding one. I'pon the atmospheric system it is no more expensive to run 

 quickly than slowly." 



The speed, excluding stoppages, would be about -iS miles an hour, in- 

 eluding stoppages — (Sarmida.) 



The Djlkty line, from its curves, is very unfavonralile for an experiment 

 of speed. I'ifly-nne miles an hour, which is the rate at which tliey have 

 travelled on the Dalkey line, is more than safety WMuld allow — (Field.) 



The whole distance from Exeter to Plymouth could be traversed at a speed 

 of CO miles an hiiur^(limnel.) 



On the atmospheric system it will not cost the railway company more to 

 carry the putilic at a quiik rate than at a slow one ; they will have no tempta- 

 tion to limit the speeil of travelling within any bounds that ought to satisfy 

 reason. Extr.norilinary speed was attained by the piston-carriage on the 

 Dalkey line, delarhed' from the train; Mr. EIrington stated it to be at an 

 average speed of 84 miles an hour ; on a long line of 200 or .■JOO ndles one 

 or two light trains might be sent eai'h day with letters at the rate of 100 

 miles an hour — (llotfinson.) 



" Mr. Stephenson lays down in that report an extremrly singular criterion 

 of the maximum velocity being arrived at. In that, or in his evidence before 

 the Croydon committee, be states that be is certain the maximum velocity 

 was attained, because the barometer gauge did not rise ; now an extreme 

 cat* will show that that test is incorrect. Suppose the tube were perfectly 



freed from air — perfectly exhausted, then the piston would sustain on one 

 side the full atmospheric pressure of 1,5 pounds to the square inch, and no 

 pressure on the other side; it is clear that the motion of the piston and the 

 train would go on accelerating, because there would he nothing to cheek it. 

 It would go on accelerating as long as the piston was in the tube, until the 

 resistance of the air to the train balanced the pressure. Now you see that, 

 in this case, the gauge must remain at 30 inches, notwithstanding the ex- 

 treme acceleration. That will show at once that the stationary condition of 

 the gauge has nothing to say to the velocity. The real criterion of the 

 maximum velocity being attained is, that the dilfercnce between the external 

 pressure of the atmophcre and the prc;,sure of the air in front, shall be 

 greater than the amount of the resistances to Ine motion of the train. So 

 lung as that is the case, so long the motion will continue to be accelerated, 

 even though the gauge may he sinking. The sole argument by which Mr. 

 Stevenson endeavoured to prove that the maxiinnm velocity was attained, 

 viz. the stationary condition of the gauge, is therefore an evidence that the 

 motion was still accelerating, unless it be also shewn that its height was 

 such as to indicate a pressure equal to the resiatance." 



In experiments on the Dalkey line witness found the smallest height of 

 mercury in the guage gave the greatest velocity ; the maximum velocity was 

 rather under -10 miles an hour ; the height of the mercury about 15 or IG 

 inches. As the vacuum increased there was an increased loss of power and 

 diminution of velocity. Explanation of the ditl'erence of opinion existing be- 

 tween Dr. Robinson and witness as to the circumstance stated in witness's 

 report, that the greatest velocity is attained whcu the position of the baro- 

 meter becomes uniform — (Stephenson.) 



" Can you explain the difference of opinion which exists between Dr. 

 Robinson and yourself, as to the circumstance stated in your report, that 

 you had attained* the masiranm velocity when the position of the barometer 

 became uniform .' — I can, and I. should be glad of the opportunity of ex- 

 plaining it. Dr. Robinson puts a position, by way of illustrating what he 

 conceives to be an error which I have fallen into ; be supposes a perfect va- 

 cuum to be made before the piston in the pump; he says, therefore, that it 

 would go on accelerating till the resistance of the atmosphere to the carriage 

 exactly equalled the power of the piston ; here, he says, the velocity will de- 

 pend upon the resistance of the atmosphere, which has nothing to do with 

 tl'.c barometer; eri/o, the barometer can have nothing to do with the velocity. 

 1 was perfectly aware of that view, and I will explain to the committee how 

 I endeavoured to guard aeainst any error arising from that circumstance. I 

 quite anticipated, when the experiments were made, the objection which Dr. 

 Robinson has now started ; because, if you observe the experiments which I 

 tried, von will see that one or two in the first instance overran the tube ; 

 they did not get a steady height of the barometer, they ran much more 

 quickly than we wished ; but they ran more quickly merely from this cir- 

 cumstance, that they employed the engine in pumping the vacuum before 

 they allowed it to produce any beneficial effect upon the train ; therefore, 

 during the time that the carriage was passing over the Dalkey plane, it was 

 not only receiving the power given by the pumping from the engine during 

 the time it was moving, but it was receiving the result of the previous work- 

 ing; it was receiving the expenditure of the working that had been husbanded 

 before it started. Now if that accumulation of power befoie the train was 

 allowed to start was so great as not to be exhausted before the carriage gets 

 to the end of the plane, it must go on accelerating, and the barometer of 

 course will not indicate the velocity ; but if you take care to generate only 

 so much power before the train starts as will exhaust itself before the car. 

 riage reaches the top of the Dalkey plane, then you get the true result, be- 

 cause then you go on accelerating until the resistance equals the power ; as 

 soon as the'resistance equals the power, the velocity must be uniform, and 

 the barometer must be stationary, because it cannot be stationary unless the 

 velocity is uniform. If the air were drawn away more quickly than the pis- 

 ton could follow it, an acceleration would instantly take place ; if it were 

 not drawn away, there would be more compression, and therefore the baro- 

 meter would f^all ; therefore, though I do not say that the height of the 

 barometer is actually a test of the velocity, yet 1 say that it is a test of the 

 uniformity of the train, and the position which Dr. Robinson puts an impos- 

 sible one ; he supposes a perfect vacuum made, which is not the fact, and 

 cannot be the fact." 



Relative Speed of the Locomotive and Atmospheric Systems. — Reasons for 

 considering that no greater speed is likely to be attained, as a general rule, 

 upon the atmospheric than upon the locomotive system ; cases in which the 

 locomotive would beat the aloiospheric — (Stephenson.) 



" I compared the working of the Dalkey line on the atmospheric system 

 with the working of the Eustmi Plane from Euston-square to Camden lown, 

 bv means of a rope, and 1 found that the quantity of power lost by the fric- 

 tion of the rope in the one case was, as nearly as possible, equivalent to the 

 loss in the other case by leakage; and that is given in my report at length. 

 I give the amount of duty done by each machine, and the comparative power 

 of each. You stated that at 1 mile in the one case to 1 5 in the other .' — Yes. 

 At what vacuum was that.' — I assumed the vacuum to be from IGto IS 

 inihes. I made a calculation upon the Dalkey, with trains, which I con- 

 sidered equivalent to the trains upon the Euston Plane ; therefore the cases 

 were very neaily the same. At what rate of speed did you calculate the 

 train to be going? — Eighteen to twenty miles an hour; that is the rate in 

 each case. At a rate of from IH to 20 miles an hour the friction of 1 mile 

 of lope was equal to the leakage of 11 mile upon the atmospheric liue ? — 



