210 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Mat, 



cation especially in point of power, where they consider the economy resulting froni its 

 adoDtion would be found most t-onspicuous and decisive. But as the circumstances nt 

 this case are pecuhar, and their introduction here would interrupt the natural course of 

 investigation I shall append to this Report a few observations on the subject, furnished at 

 my request by Mr. G. P. Bidder, who has particularly devoted his attention to the appli- 

 cation ot the atmospheric system to that railway. 



Locomotive Power. 



I will now proceed to inquire whether the capacity of the locomotive engine and the 

 loss of power by the locomotive system exceed or fall short of that indicated by the expe- 

 riments upon which this Report is based. The 4th Train in Table No. III. being that in 

 which the greatest velocity was attained, it is taken as the most advantageous to the new 

 system under discussion : the load in this case was 2t5-5 tors, and the velocity 34-7 miles 

 per hour was attained on a rise of 1 in 115, presenting a resistance of 1311 lb., including 

 the friction, gravity, and resistance of the atmosphere. In overcoming this resistance, 

 the experiment shows a loss by the atmospheric system of 53 per cent. Now a locome- 

 tive engine under these circumstances, in addition to the 13111b., must ove'^come the 

 friction, gravity, and atmospheric resistance of the engine and tender, which ia about 

 900 lb., together with a further resistance arising from the pressure of the atmosphere 

 against the pistons, peculiar to the working of a locomotive, as it is a non-condensing 

 engine ; these will amount to 32 and 22 per cent, respectively, or togsther to 54 per cent, 

 of the total power developed by the engine. In this comparison, I have neglected the 

 friction of the working gear of the engine, as this is also omitted in the stationary engine, 

 the indicator diagrams at Kingstown being taken from the air jiump and not from the 

 steam cylinder. I have also not noticed the loss that would arise from the slipping of 

 the wheels, when a locomotive eng ne is worked upon so steep a gradient. The loss of 

 power, therefore, by the use of the locomotive engine under such circumstances, appears 

 somewhat to exceed that shown by the atmospheric system ; this is, however, a most dis- 

 advantageous comparison for the locomotive engine, because the gradient far exceeds that 

 upon which it can be worked economically. 



When the load is augmented, the loss by the locomotive engine is slightly decreased, 

 and the per centage lost of the total power is therefore diminished ; while \vith the at- 

 mospheric system, thp per centage of loss is considerably increased, amounting to 77 per 

 cent, with a train of tU-7 tons. These considerations show that with small trains the 

 expenditure of power by the atmospheric system is less than by locomotive engines on this 

 gradientof 1 in 115; whilst on the other hand, whenever the resistance of the train is 

 such that a high vacuum is required, the locomotive has the advantage over the atmos- 

 pheric system, . . 



The Ughtest trains taken upon the Kingstown and Dalkey incline at the velocities re- 

 corded probably exceed the capabilities of locomotive engines, and so far prove that the 

 atmospheric system is capable of being applied to somewhat steeper gradients, and that 

 on such gradients a greater speed may be maintained than with locomotive engines. It 

 must be observed, however, that this advantage is not peculiar to the atmospheric system, 

 but necessarily accompanies every system consisting of a series of stationary engines, in 

 which the gravity of the moving power forms no part of the resistance to motion. 



If we convert the loads moved in the experiments into equivalent loads on a level, 

 we shall then find that in no case they exceed the duty which is being daily performed by 

 locomotive engines. Thus, taking experiment No. 4, the load being 26-5 tons, the resist, 

 ance per ton upon an incline of 1 in 115, at a velocity of 34.7 miles per hour, estimating 

 the resistance of the atmosphere according to Larduer's experiments previously referred 

 to, will stand thus: — 



Gravity . . .20 lb. per ton. 



Friction . . . 10 „ 



Atmosphere . . .20 „ 



Total resistance . . 50 

 And the resistance upon a level will be, 



Friction . . .10 lb. per ton. 



Atmosphere . . . 20 „ 



Total resistance . . 30 



Therefore, this train of 26*5 tons, on the incline of 1 in 115, will be equivalent to 44 tons 

 upon a level, at the same speed of 34*7 miles per hour. This duty, which is indisputably 

 the utmost given by the experiments at Kingstown, is much exceed<?d daily on many lines 

 of railway in this countrj-. and especially by the Great M'estern, and Northern and 

 Eastern. Throughout the experiments, it will be seen that the duty performed by the 

 Kingstown and Dalkey engine, when reduced to an equivalent level, falls short of the 

 daily performance of locomotive engines on our piincipal lines of railway, both as regards 

 speed and load. 



When the comparison is made by applying the locomotive engine to the circumstances 

 of the Kingstown and Dalkey incline, the atmospheric system becomes the more advan- 

 tageous. Such a comparison, however, cannot be held as strictly correct, because the 

 locomotive engine, as a motive power on steep gradients, is wasteful, expensive, and un- 

 certain ; therefore, on a long series of bad gradients, extending over several miles, where 

 the kind of traffic is such that it is essential to avoid intermediate stoppages, the atmos- 

 pheric system would be the more expedient. If, however, intermediate stoppages are not 

 objectionable, as is the case in the conveyance of heavy goods and mineral trains on the 

 railways in the neighbourhood of Newcastle-upon-Tyne, the application of the rope is 

 preferable to the atmospheric system. This conclusion I conceive to be fully established 

 by the comparison which has been made between the Kingstown and Euston inclines. 

 Again, on lines of railway wher» moderate gradients are attainable at a reasonable ex- 

 pense, the locomotive engine is decidedly superior, both as regards power and speed, to 

 any results developed or likely to be developed by the atmospheric system. 



In considering these last, as well as all the preceding calculations and remarks, it must 

 be borne in mind that they have reference solely to the question of power, and are en- 

 tirely independent of the question of expense or convenience : the next step in the in- 

 quiry will therefore be, the expense of constructing lines on each system, and the proba- 

 ble cost of working. 



In approaching this question, it is desirable first to ascertain how far it may be practi- 

 cable to work with a single line of vacuum tube, which is certainly by some considered 

 feasible even on great public railways. It does not, however, require much consideration 

 to prove that a single line of tube would be quite inadequate to accommodate any ordinary 

 traffic, such as exists on the principal lines in this country. It has therefore been urged 

 by those who regard the capacity of the atmospheric system as almost unlimited, that a 

 train may be dispatched every half hour, or even every quarter of an hour ; but in making 

 this observation, they entirely overlook the circumstance, that this very advantage, in 

 respect of the number of trains, is fatal to the sufficiency of one line of tube for any con- 

 siderable length of railway. 



Suppose, for example, a line of railway for 112 miles length were divided into stages of 

 3i miles each, as proposed by the inventors ; if a train were dispatched from each end 

 every half hour for 12 hours, and the speed of about 37 miles per hour, including the stop- 

 pages for traffic, could be attained, there would be a train at every 10 mites of line, aud 

 each train in its journey would meet U other trains with whose progress it would inter- 

 fere ; in short, each train would of necessity be stopped 11 times, and delayed until the 

 train occupying the section of the tube had quitted it, and the tube had been again ex- 

 hausted. Such a series of stoppages would, it is plain, give rise to so great an amount of 

 delay, as would render the use of a double line of tube absolutely imperative. In the 

 example just brought forward by way of illustration, the mean speed assumed is 37 miles 



per hour, the whole time of the journey would therefore be thiee hours ; but the eleven 

 stoppages occupying at least ten minutes each, which is very considerably below what 

 practice would require, would, notwithstanding the great velocity assumed, extend the 

 time to five hours. But let it be remembered that these stoppages cause additional 

 meeting of trains, involving increased delay, and the time is consequently augmented to "i 

 hours. Or if the mean velocity be reduced to 30 miles jier hour, which is now the 

 greatest mean rate on any railway, the total time of the journey will be thus increased to 

 10 hours 



We must therefore assume a double line of pipe, and thus the principal difficulty just 

 pointed out is certainly removed ; but the addition of a double line involves another 

 scarcely less formidable, when the expense of the system is the subject under discussion. 

 The absolute stoppage of trains is avoided, but a most decided and large reduction ot 

 speed must still necessarily arise at the stations where the trains intersect, unless a sepa- 

 rate series of stationary engines be erected for each line of I nbe ; because the engine must 

 be occupied in exhausting 7 miles of tube at once, which would detract very considerably 

 from the velocity. Such a reduction is quite inadmissable if we are to view the system as 

 applied to the great thoroughfares of this country; in which case I am confident that 

 every perfection of which it is susceptible must be carried out. 



The difficulty suggested as calling fcr duplicate series of stationary engines, may at first 

 sight appear sr.rmountable by confining the duplication to the points where the trains 

 meet, and thereby avoiding a large addition to the original outlay in establishing the 

 system upon a long line of railway : this, however, presupposes that the trains are not 

 started so frequently as every half hour, since that would occasion the duplication of 

 every engine. But this will not be found to be the case, because the intersections of the 

 trains cannot possibly be made to take place always at the same points, even on the sup- 

 position that each railway is worked independently of every other with whicli it maybe in 

 connection. When we introduce in addition, the fact that several branch lines must ne- 

 cessarily flow into the main trunks, that no line can be worked independently, that the 

 arrival of trains is, and must always be, subject to much irregularity, sometimes arising 

 from their local arrangements, sometimes from weather, and at others, from contingen- 

 cies inseparable from so complicated a machine as a railway, — it must be palpable that 

 two independent series of stationary engines is as indispensable as two independent lines 

 of vacuum tube, for the accomplishment of that certainty, regularity, and dispatch, which 

 already characterise ordinary railway operations. 



If what has been urged be thought inconclusive with reference to the duplicate series of 

 stationary engines, the alternative of checking or stopping each train at the points where 

 tliey meet must be admitted as inevitable, because two lengths or sections of tube mustbe 

 under the process of exhaustion at one time by the same engine ; we have, therefore, to 

 inquire into the practicability of exhausting 7 miles of tube by the engine erected and cal- 

 culated as only adequate to the efficient exhaustion of 3^ miles length. The calculations 

 made in the previous part of this Report, on the subject of leakage, prove that any attempt 

 to work a line in this manner, would involve such a diminution of velocity at each inter- 

 section of trains as could not fail to extend its influence, and produce great irregxdarity 

 throughout the system, when confined even to one independent line of railway; and this 

 would apply, in an exaggerated degree, to the numerous tributary streams of traffic which 

 must flow sooner or later into all the main thoroughfares of railway communication, at 

 points, and under conditions, which cannot at this moment be anticipated. Another very 

 strong reason for these double engines being required, is, that in case of any failure to one 

 of the engines, the whole traffic of an entire district of country would be stopped, and a 

 duplicate engine at each station would be required to provide against this contingency, 

 were it not also rendered necessary by the reasons already considered. 



These facts in reference to the expense of construction (tor I regard them in no other 

 light than as facts, because they are the inevitable consequences which must attach them- 

 selves to this system wherever applied,) lead me to estimate the oiiginal cost much higher 

 than any amount which has been calculated upon by those who have made their opinions 

 public on this subject. 



Comparative Estimates. 



Mr. Samuda gave Sir Frederick Smith and Professor Barlow a calculation of cost, for 

 average loads of 30 tons at the rate of 30 miles per hour, for a single line of atmospheric 

 railway. Since Mr. Samuda furnished this calculation, experience at Kingstown has pro- 

 duced some modification in the proportions of the engines and vacuum tube : the follow- 

 ing is now his estimate of cost for the apparatus as applicable to such lines of railway aa 

 the London and Birmingham. 



Cost per Mile in Length, 



Vacuum tube, 15 inches diameter , . ^1,632 



Longitudinal valve, &c. . . . 770 



Composition for lining and valve groove . 250 



Planing, drilling, &c. . . . . 295 



Laying, jointing, &c. . . . . 295 



Station valves and piston apparatus . • 100 



3,342 

 Engine, 100 horse-power, with pump, &c. J£4,250 

 Engine-house, chimney, &c. . . 450 



Total for 3^ miles 

 Cost per mile in length 



±•4,700 



1,343 



Total cost per mile . • . £4,685 



It will be observed that Mr. Samuda has only estimated for the a single line of vacuum 

 tube and a single series of engines, under the impression that such an arrangement is 

 adequate to meet every necessity. But from what has been said on this part of the sub- 

 ject, I think it is made evident, that such a limitation in the arrangements on any im- 

 portant line of communication would be very inexpedient, to say the least. I have conse- 

 quently revised this estimate, and the following appears to me to be the minimum expense 

 at which the atmospheric apparatus could be applied to any extensive line of railway. 



Cost per Mile in Length. 



Vacuum tube 15 inches diameter 



2 engines of 250 h. p. each, (at 33,000 lb.) with 



pumps, &c. complete, at £25 per h. p."^ £12,500 



Engine-house, chimney, reservoir or well . 1,500 



£7,000 



Total for 3^ miles 

 Cost per mile in length 



Total cost per mile 



. £14,000 



. 4,000 

 £11,000 



1 The power of each of these engines appears at first vei7 great when contpared with 

 that given in Mr. Samuda's estimate, but the real comparison upon the same standard of 

 commercial h. p. will be 125 to 100. 



