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tion or division of the line, being made selfacting, there will be no occasion for stopping, or even for retarding the movement of the train, in passing from one division of the pipe to another, as the air is successively exhausted by the stationary power placed at the proper intervals. The carriages may, therefore, pass continuously, at any required velocity, as if drawn by a locomotive engine; and it is necessary to keep this circumstance in mind, as by any other system of traction by stationary engines than the atmospheric, a stoppage and a change at each engine is unavoidable." Pages 9-10.
Soon after Mr. Clegg had taken out his patent, he exhibited a model 30 feet long at Paris; and a second model, 120 feet long, was erected in 1840, by Messrs. Samuda at cited much attention. In the autumn of their manufactory in Southwark, which exthe same year a space of ground at Wormholt Scrubs, half a mile long, was placed by the directors of the Thames Junction Railway Company at the disposal of Messrs. Clegg and Samuda, (who co-operated in carrying out the invention,) for the purpose of laying down a line of railway on the at
It is difficult to appreciate fully the sim-mospheric principle; and in May, 1840, plicity and beauty of this invention, and the this experimental line was opened. An facility and regularity with which the tube event so interesting attracted a large conand valves act, without examining the appa- course of persons to the spot; and by the ratus or plans of its construction. The issue of the experiment then to be tried, exhaustion of the main tube, and the propulsion of the piston and carriages attached, are easily comprehended; but the mode of passing from one section of the pipe to another, above alluded to, requires more attention: this is explained in the description given by M. Teisserenc in his Report to the French Government, to which we shall presently allude:
would probably be shown the practicability or failure of the invention: several members of the Cabinet, and a large number of persons of rank and eminent engineers were present. The success which from the first attended these experiments realized the expectations of Messrs. Clegg and Samuda; they were repeated several times each week during a twelvemonth, and continued less frequently a second year. Engineers and
came from Paris, Petersburg, Vienna, Berlin and other parts of the continent, as well as from every part of the British dominions, to examine the apparatus and witness its operation. The results of these experiments appeared in a pamphlet in 1840, which was reprinted in an extended form in 1841. We shall refer to the points of chief interest.
The inclination of the line was 1 in 120; the vacuum-pipe half a mile long and 9 inches internal diameter; the exhaustingpump was 37 inches diameter and 224 inches stroke, worked by a steam-engine of 16-horse power.
"Quand on sort de la sphère d'action d'une ma-persons connected with railway companies chine pneumatique, pour entrer dans la sphère d'action de l'appareil pneumatique suivant, il est donc convenable que l'air du tube dans lequel on entre soit dejà raréfié; mais alors le tube est fermé à ses deux extrémités. Nouvelle difficulté pour éviter le choc du piston arrivant avec toute sa vitesse acquise contre la soupape de clôture, pour ouvrir cette soupape avec un petit effort, de manière à donner passage au piston, sans donner passage à l'air extérieur, sans arrêter, sans ralentir seulement le convoi. Ici il a fallu encore_recourir à une disposition fort ingénieuse. La soupape de MM. Clegg et Samuda s'ouvre au moment où le piston ferme déjà le tube, et par l'action même du piston; l'effort est presque nul, la rentrée de l'air n'en est pas augmentée. Quant à la sortie du piston d'un tube, elle ne donne lieu non plus à aucun choc, bien qu'une sou"For the purpose of experim ent, a series of pape de clôture se trouve aussi à l'extrémité du posts were fixed along the half mile every two tuyau, et voici comment: l'appareil pneumat-chains, and a barometric gauge was attached ique placé sur le côté du chemin communique at each end of the pipe, for the purpose of asavec le tube de propulsion par un tube aspira- certaining the degree to which the pipe was teur. Il a suffi de placer ce tuyau aspirateur à quelques mètres en deçà de l'extrémité fermée par la soupape de sortie rendre toute pour rencontre entre le piston et cette soupape impossible. Dès que le piston a dépassé le tube aspirateur, l'air n'étant plus enlevé devant lui se comprime de plus en plus, augmente progressivement de densité jusqu'au moment où la pression intérieure étant supérieure à la pression atmosphérique, la soupape s'ouvre d'elle-même.”—M. Teisserenc's Report, p. 112.
exhausted. A vacuum equal to a column of mercury eighteen inches high was obtained in about one minute, and both gauges indicated the same extent of vacuum at the same in
tained during six months, it was found that Following out the registered results oba main pipe of 18 inches diameter would be sufficiently large for a traffic of 5000 tons a day, viz. 2500 each way, supposing the in
clination of the line to average 1 in 100.* But among the most important of the facts deduced from these experiments are the following, which refer to the effects of wear and tear on the apparatus:
"The workings of the system are equally perfect during all seasons,-through the height of summer and in the severest winter that we have known for many years: in no single instance during the whole time has any derangement of the machinery taken place, to prevent, or even to delay for one minute, the starting of the trains. The main pipe and valve have considerably improved by working; the composition for sealing the valve has become so much more firmly bedded in its place, that while in June last we were only able to obtain a vacuum equal to a column of mercury 19 to 20 inches high, we now obtain from 22 to 24 inches, and occasionally 25. The speed, originally from 20 to 30 miles per hour,
now ranges from 30 to 45. The whole attendance the valve and main received during this period was that of a single laborer for about *The Patentees give the following details:"A main pipe, 18 inches diameter, will contain a piston of 254 inches area: the usual pressure on this piston, produced by exhausting the pipe, should be lbs. per square inch (as this is the most economical degree of vacuum to work at,
and a large margin is left for obtaining higher
[one hour every week; the composition now in the valve-groove has never been changed; and 56 lbs. weight only has been added to which consists of wax and tallow, is Is. per lb.” supply the waste; the cost of this composition. -Page 11.
The success of these experiments, and the general attention which was drawn to the subject, forced it upon the notice of the Government. Mr. Pim, who took a warm interest in the promotion of so important an enterprise, printed a detailed description of the atmospheric railway, the great public advantages which its adoption held out, and urged the subject strongly on the attention of the Board of Trade. In conse quence of this appeal, Sir Frederick Smith and Professor Barlow were appointed to examine the experimental works at Wormholt Scrubs, and to furnish a report upon the applicability of the system. This document, addressed to the Earl of Ripon, was presented to Parliament, and is dated February 15, 1842. It contents consist chiefly of calculations on the details of working, too purely scientific for our examination here. We cannot, however, but notice the partiality of the general remarks, the eviIdent desire to suggest every doubt and to minimize every advantage of the atmospheric system. Notwithstanding this bias, however, the admissions forced upon its authors are decisive. The chief points on which questions naturally present them
our attention, are the following: we quote them from the Parliamentary Report :
vacuums to draw trains heavier than usual on emergencies, a tractive force of 2032 pounds is thus obtained, which will draw a train weighing 45 tons, at 30 miles per hour, up an incline rising 1 in 100. Two and a half miles of this pipe will contain 23,324 cubic feet of air, ths of which, or 12,439 cubic feet, must be pumped out to effect a vacuum equal to 8 lbs. per square inch; the air-selves, and to which we shall first confine pump for this purpose should be 5 feet 7 inches diameter, or 247 feet area, and its piston should move through 220 feet per minute, thus discharging at the rate of 24 7 X 220=5434 cubic feet per minute at first, and at the rate of 2536 cubic feet per minute when the vacuum has advanced to 16 inches mercury, or 8 lbs. per square inch, the mean quantity discharged being thus 3985 feet per minute: therefore 31 minutes, the time required to exhaust the pipe; and as the area of the pump-piston is 14 times as great as that in the pipe, so the velocity of the latter will be 14 times as great as that of the former, or 220 feet per minute X 14 = 3080 feet per minute, or 35 miles per hour. But in consequence of the im
perfect action of an air-pump, slight leakages, etc., this velocity will be reduced to 30 miles per hour, and the time requisite to make the vacuum increased to 4 minutes: the train will thus move over the 2 1-2 miles section in 5 minutes, and it can be prepared for the next train in 4 minutes more,-together 9 minutes; 15 minutes is therefore ample time to allow between each train, and supposing the working day to consist of 14 hours, 56 trains can be started in each direction, or 2520 tons, making a total of 5000
tons per day. The fixed engine to perform this duty will be 110 horses' power, equivalent to 22 horses' power per mile in each direction."
"It is no longer a question whether trains of carriages may be worked by means of atmospheric pressure; the points now to be decided are:
"1. Whether this principle admit of its being advantageously applied to greater distances than half a mile, which is the length of the present experimental line" [at Wormholt Scrubs].
"2. The probable expense of constructing a railway on this principle, and of supplying the locomotive power.
"3. The relative economy in working such a line, as compared with a railway worked by locomotive engines.
"4. The degree of safety which the atmospheric system affords, as compared with other locomotive means."
The first of these points appears to be decided, by the successful results obtained on the railway from Kingstown to Dalkey, extending nearly two miles, which has been
recently completed: these are still more satisfactory than the former experiments on a line of half a mile; but we shall have occasion to refer to them hereafter. We shall here quote the observations of Mr. Samuda on this point :
tion, we now possess satisfactory data upon which to form a calculation. In the first place, on the atmospheric system one line of rails is proved to be sufficient, and half the expense of rails is thus at once saved. But in addition to this, the weight of the rail may be reduced very considerably, in consequence of the weight of the locomotive engine (from fifteen to twenty tons) being got rid of.
Another considerable saving is effected in the expense of forming the road. Those who have studied the cost of constructing railways, know well how large an item this forms. A slight inclination in the course renders a succession of embankments, cuttings, viaducts, etc., necessary, which have not only to be made in the first instance, but to be maintained and repaired. The cost of this is too obvious, to any one who has travelled on our present lines of railway, to need indication.
-"In answer to the first objection we would say, in every case where a train has been started, the pipe has first been exhausted to 18 inches of mercury or upwards. .... From the barometric gauges fixed at both ends of M. Mallet, in his recent Report to the the pipe, the vacuum is ascertained to be French Government, (to which we shall formed to an equal extent throughout the refer hereafter), makes another valuable whole length without any appreciable difference of time. The pipe laid down is 9 inches suggestion, which will probably lead to a diameter, and half a mile long, and a pressure further saving :"6 Could we not besides equal to a column of mercury 18 inches high (as is done on the road from Kingstown to is obtained in one minute by an air pump 37 Dalkey, where the trains run more than 500 inches diameter, moving through 165 feet per mètres by momentum, the piston out of the minute. Now it is obvious that, if the trans- pipe) have long interruptions of the main verse section of the pipe be increased to any pipes, at the ends of which the trains arrivextent, and the area of the air-pump proporving at new mains should regain their lost tionately increased, the result will remain unaltered,-i. e. half a mile of pipe will be ex- speed. Great economy would follow such hausted in one minute; and supposing the air- an arrangement. Of the different combipump has to exhaust 3 miles, it will perform nations which might thus be formed, much the operation in 6 minutes; it is also obvious yet remains to be said."-Page 44. that if the area of the air-pump be increased in a greater proportion than that of the pipe, the exhaustion will be performed more rapidly; or vice versa. These results are matters of absolute certainty, as convincingly clear as that the power of a steam-engine must be regulated by the area of the piston on which the steam acts. No person of scientific attainments will for one moment doubt that, if a steam-engine were made with a cylinder twice the area of the largest cylinder ever set to work, the power obtained would be in proportion to the increased area. And so with the airpumps before alluded to; the excess of work is immediately arrived at, that an air-pump 6 feet 3 inches diameter will perform over another of 3 feet 1 inch diameter, the speed of the pistons being the same in both instances. "This width, more than quadruple that of So plain and self-evident is this result, that we the road, is rendered necessary by-First, the believe the most skeptical will admit it to be foundation of the slopes required by the cutcorrect; and this being granted, the applica- tings and embankments. Secondly, the spoil bility of the system to a line of any length banks. Thirdly, the side roads. Fourthly, must follow; for whatever the length of rail- the drains or ditches; and Fifthly and lastly, road be,-whether 3, or 30, or 300 miles,-no the sidings for stations on the line. Of these different effects have to be produced. The five causes the principal is the foundations for working a road 30 miles long would be the the slopes, which are often very considerable. same thing as working 10 roads each 3 miles The necessity of great radii of curvature, and long. Every 3 miles an engine and air-pump especially that of small inclinations, leads inis fixed, which exhausts its own portion of pipe evitably to this. With the Atmospheric sysbefore the train arrives; thus, as the train ad- tem, the earthworks, and consequently the exvances, it receives power from each succeed-tent of the slopes, will be much less consideraing engine in turn (and without any stoppage, ble. To estimate the cost of compensation on unless required, until it arrives at its final des- this system at five-ninths of that on the orditination), and the air-pumps continuing to nary railroads would be to overrate this part work, after the train has passed, on the section of the expense.”—Page 40. they act upon, re-exhaust it in readiness for the
M. Mallet, in speaking of the width of way required on the present system, says :—
"Passing now to works of art, I shall re2. With respect to the cost of construc-mark that a great number among them, as
bridges, under which the railroad passes, will be considerably reduced in their dimensions. Instead of a height of 5m. 50 under the crown these bridges will need to have no more than 3m 50 at most, since it will not be necessary to leave passage for the chimneys of the loco motives. The quantity of embankment at the approaches to these bridges will be proportionally less."-Page 41.
The fact has never been questioned, that the atmospheric railway admits of much steeper gradients; and, without entering on the wide field of calculations of economy and public advantage which this simple fact opens, we shall limit our remarks to one point of view, and leave our readers to follow out the deducible reasonings. A locomotive engine weighing 17 tons will only draw a load of about 30 tons up an inclined plane of 1 in 100 at the rate of 20 miles an hour. If required to draw any additional weight, at this small speed, another engine must be attached,—that is, the cost of working must be doubled. This is alluded to by M. Teisserenc:
"Ne pouvant diviser les trains, ni créer à volonté des trains supplementaires, aussitôt qu'un convoi est trop chargé, il faut atteler deux locomotives, c'est-à-dire doubler les frais de transport. Les accidents sur les trains menés à très-grande vitesse ont d'autant plus de gravité que le nombre des voitures attelées est plus considérable. Non seulement ils frappent un plus grand nombre de personnes, mais la masse en mouvement étant plus grande, les chocs, en cas d'arrêt brusque, sont plus difficiles à amortir, plus désastreux dans leurs conséquences."-Page 107.
ing calculations which the present system, with its stringent conditions, does not admit of." To overcome the resistance of a load up a steep hill, the power of the engine must be increased; and it is only a question, in each particular instance, whether this will be more expensive than tunnelling or embanking. The Parliamentary Reporters remark, that "to work steep inclines by means of larger tubes would involve the necessity of stopping the train at the foot of such planes, and of again overcoming the inertia of the load; in both instances causing a loss of time." This objection is answered by Mr. Bergin as fol
"Assume for a moment, which however I altogether deny, that it was necessary to vary the size of the main on every ascent, and to stop the train at the foot thereof, for the purpose of changing the piston, I should say the cases are very few indeed in which the engineer, when laying out a line of railway, could not so arrange his plans that these stopping places should be the most desirable for stations, and thus render the accommodation afforded to the public perfectly compatible with the efficient and economical working of the line. But I do not agree in supposing it necessary to change the dimensions of the main on every steep incline ;.........the less the exhaustion in the main, the greater the quantity of air extracted at each stroke of the pump in proportion to the power expended; or, in other words, the less the exhaustion (within proper limits) the diameter of the main being proportionately increased, the greater the economy of the system; and in this assertion I am fully borne out by the Reporters' investigation. Further, this reduction of vacuum does not materially affect We now turn to the atmospheric princi- the velocity of travelling, which is essentially ple. The stationary engine of 100 horse- dependent on the discharging power of the power, now at work on the Dalkey railway, when looking out a line of railway, and startair-pump. Such being the fact, an engineer, draws 72 tons at 20 miles an hour, along a ing with the knowledge that he is not restricted line of 13 miles upon a gradient of 1 in to levels or even to moderate gradients, would 100. The Parliamentary Reporters admit find few districts in which he would not be that, whilst a great part of the power of able to form the railway almost on the very the heavy locomotive engine is expended surface of the country; for he would be at in overcoming its own gravity and resist-liberty to avail himself of almost any ascent; the only consequence of his doing so being an ance, it is equally true that, on the atmoincreased expenditure of power, precisely in spheric principle, the whole additional force the ratio of the increased resistance." is exerted on the load itself." This advantage of the atmospheric principle consequently admits the power of working lines. There are many other incidental advaneconomically on a large range of gradients tages, of an importance scarcely yet apprefrom which locomotive power is necessarily ciable, which are obtained by the simple excluded; the question of limit is, in fact, command of steeper gradients. It will be one not of power, but of economical calcu- seen that this opens at once a much wider lation. "The atmospheric system," says and more free choice to the engineer in the M. Mallet, "is, so to speak, master of the course of his line, and the expenses of comacclivities, and affords opportunities of mak-pensation for the value of property may fre
quently be affected and considerably re- | of fifty to sixty miles an hour, upon an orEduced or avoided. dinary line, as at twenty miles,-with the Independent, however, of mere economi- remarkable advantage, that increase of cal considerations, we remark the incalcu-speed does not increase the cost. In some lable advantage of effecting the possibility respects, the tendency of increase of speed of railroads in countries where locomotive is even to lessen cost; for instance, it has power must ever remain inapplicable.-been shown that the leakage is diminished Mountains may be bored, valleys may be in proportion to speed, and a saving is thus bridged with viaducts, or filled up with em- effected. Assuming, therefore, on the other bankments, but the power to effect this hand, that the traffic on a line renders it does not depend merely upon skill and the desirable to start trains every quarter in command of capital; it is restricted within stead of every half hour, it is easily accomthe limits of prudential economy, of that plished. The statement of the Parliamenforesight in man which regulates expendi- tary Reporters shows how the economy on ture by anticipated profit,-which plants the atmospheric system would increase in the grain, that it may increase and multi- such cases. And here we must remark a ply. These gigantic works will only be singular advantage of employing stationary undertaken where the existing or antici- engines, alluded to by M. Teisserenc.* pated traffic justifies the speculation; and The cost of a locomotive engine, in action, we may hence estimate, in some degree, is nearly the same whatever load it draws; the value of an invention which offers so and the cost of repairs is proportionably wide an extension of these advantages of smaller upon an engine of large size and communication, whilst it holds out increased power; such a motive power can therefore inducements of profit to enterprising capi- be only profitably worked with large trains, talists to promote the public benefit. and this very fact tends to limit considera
3. We now proceed to the relative ex-bly the number of daily trains, and consepenses of working, on which point the Par- quently the advantages of railway travelliamentary Reporters make the following ling.t A necessary regard to public securemarks:
number of trains started in a day (without reference to their load), the more economical is the system of working. By the registered experiments on the Dalkey railway,
rity leads to the same conclusion. The rapid succession of trains upon a line is a "This a question to which no general anconstant source of danger, and delays are swer can be given, because it depends entirely on the daily amount of traffic. We have no therefore unavoidable. Upon an atmosphedoubt that a stationary engine properly pro-ric railway, on the contrary, the greater the portioned, according to the rules we have indicated for a pipe three miles long, would be able to work trains on a line every quarter of an hour, or every half hour, each way, during the day (say of 12 hours), amounting to 144 miles. Now to work this distance by a loco-a train with a load of seventy-two tons, motive engine, at the moderate estimate of 1s. takes five minutes and thirty-three seconds 4d. per mile, would amount to 91. 188., say 10l. to perform the journey of a mile and three per day; whereas the stationary engine power quarters. Now, as upon this system no would not cost one half that sum, and conse- two trains can possibly move at once on quently a saving in working expenses would the same section of pipe, no delay is rearise of 18001. or 2000l. per annum. But if
only half this duty were required, the expenses quired in starting the trains, to avoid danof the two ways of working would be much ger from their overtaking one another. As nearer equal; and again, if only half the latter duty were to be performed, that is, of trains starting only every two hours each way, the advantages would be on the side of the locomotive engine. The fact is, that in one case the expenses per diem will be nearly the same, whether working at intervals of an hour or at every quarter hour; whereas in the other the charge is nearly proportional to the work actually performed."-Report, p. 5.
This we assume to be correct; at the same time it will be borne in mind that, by ascertained facts, the atmospheric railway is now shown to work as easily at the rate
soon, therefore, as one train has passed off a section, the tube is ready to be exhausted again (which is effected in about three to five minutes), and to receive the next train immediately. Upon these facts it is easy to form any calculations; motives of economy would lead to the starting of as many, instead of as few trains as possible; and whilst no accident could by any chance occur from a rapid succession of trains, it is needless to remark that the public would be incalculably benefited.