The mode of operation is as follows: The communication between the grease cup and vessel being open, and all communication with the boiler closed, the grease is put into the cup A, and runs into the vessel B. The cock C is then turned so as to admit the steam into the vessel B, and at the same time to shut off all communication with the cup A. The cock D is then opened, and the contents of the vessel B are forced into the boiler by the pressure of steam from above.

The same instrument may be readily applied to lubricate the packing of Ď slides, without retarding, or in any way affecting, the progress of the engine. JOB ALLEN. 20, Bower-street, Commercial-road East, July 20, 1845.

Second, a mode "whereby the use of reservoirs of compressed air is combined with traction-pipes, with longitudinal valves opening inwards, and with transverse slides or valves for the compressed air to press against."

Third, a mode "whereby compressed air is returned back from the traction-pipes into reservoirs."

The manner in which these three improvements are combined in one system of traction is thus explained :

"The longitudinal valve turns inwards on a hinge, and consists of a long fillet of strong leather, or of other strong flexible substance suitable for such purposes, and the same is strengthened by means of narrow metal plates fixed on the upper side in a similar manner to what has been heretofore resorted to for strengthening the longitudinal valve of the atmospheric railway now at work, and those which are now being constructed. The upper surface of the valve is to be coated with hard grease, particularly at the bearing edges, so that when the valve is pressed outwards by the compressed air within the traction-pipe the joint will be rendered airtight. The air may, if desired, be at once forced from the pumps used into the tractionpipe, by having suitable connection-pipes between the pumps and the traction-pipe of a railway, in a similar manner (but reversing the action) to that now arranged for railways, where vacuum or partial vacuum is resorted to for obtaining the pressure of the air. But we prefer that there should, at intervals, (in a line of railway which is to be worked according to our invention,) be large reservoirs to receive air from the pumps worked by steam or other power, and that the reservoirs should be connected by pipes with the traction-pipe; and we prefer that there should be three reservoirs at each station, in order that the power employed may be as small as possible, so as by working continuously, both when the trains are moving as well as when they are not moving, the power employed may be as economical as possible; and this arrangement, we believe, will be found generally more advantageous than having large power simply in action when the trains are moving and standing motionless, yet consuming fuel when the trains are not running. The reservoirs will be strong vessels similar to large boilers, and of a strength in proportion to the degree of compression to which the air is subjected therein, which will be varied according to the peculiar circumstances of the traffic and the gradients; but we do not consider it desirable to have the air used in a high degree of compression, though the same allows of traction-pipes of less diame

ter, as will readily be understood by the engineer. We construct the reservoirs for condensed air each of a capacity equal to the contents of the length of the traction-pipe it is to work with; the valves or slides used between the reservoirs and the traction-pipes being progressively opened, so that the air may be maintained as near as may be at the same density in the traction-pipe at starting as at the end of a section of traction-pipe, for it will be understood that as the air in a reservoir is more dense at starting than at the end, the admission of the air to the traction-pipe should, at starting, be what is technically called "wire-drawn," gradually opening the valve as the air becomes less and less in its pressure in the reservoir. The traction-pipe is divided into sections by valves or slides. We prefer to use flapvalves for closing the traction-pipe transversely, and we enlarge the traction-pipes at those places where such flap-valves are to be used, so that they, when open, may be down out of the way of a passing piston, and when up, that they may have proper seats to press against, and as it is desirable to have the means of travelling in either direction by the aid of the same traction-pipe, we form two inlet valves near together at each place where air is admitted, having the inlet-pipe conveying the air from a reservoir or pump branched so as to enter under these two valves, there being suitable throttle or other valves in the branches of the pipe to determine by which way or branch the air shall enter into the traction-pipe, and according as one or other is open so will the flap-valve above be closed, and the piston will be propelled away from that valve, the valve for the time being across the traction-pipe resisting the air passing in the opposite direction, whilst the other transverse valve will be open, and over the opening where the other branch enters the traction-pipe, by which the piston will be free to pass over that other transverse válvé. By thus using flap-valves these transverse valves will close by the pressure of the air, or remain open according as the air comes in at one or other of the branch-pipes, and such flap-valves will not interfere with the passage of the piston in the way it is travelling, as the next valve will not close till after the piston has passed it, for, until that has taken place, the air would not be turned on to close that valve, and press forward the piston. The piston used is similar to that now employed in Ireland on the atmospheric railway, and which is well understood; but there is no apparatus necessary to open or close the longitudinal valve, which we prefer to have so arranged that it will have a slight tendency to fall open to allow of the passage of

the instrument which connects the pistonrod with the carriage, as is well understood; but in this case this instrument will precede the piston, the pressure of the air in the traction-pipe closing the valve as it comes up to it, and the air in the traction-pipe before the valve will pass or flow freely out of the traction-pipe through the longitudinal slit or opening. It will, however, be understood that if the tendency of the longitudinal valve to remain open is not sufficient, the flow of air out at the slit or longitudinal opening would tend to close it; if, therefore, it is preferred to have the valve so stiff as to tend to close, then the instrument connecting the piston-rod to the carriage should have a projection sufficiently long to press open the longitudinal valve some distance before the piston, to allow of space for the passage of air from the traction-pipe.

It will be evident that as the section of traction-pipe along which a train of carriages has just been moved, will be full of compressed air, and that such compressed air may be more economically returned back into a reservoir than by pumping from the atmosphere, for it will be understood, that in again filling a reservoir from the atmosphere, the pressure on one side of the pump piston would be the atmosphere, and on the other side the pressure due to the compressed state of the air remaining in the reservoir, and that pressure would be continnally increasing, the pressure of the atmosphere remaining constant; whereas if the air be returned from the traction-pipe into a reservoir, the pump piston will commence from a state of equilibrium, consequently requiring comparatively little power, such power increasing as the density of the air remaining in the traction-pipe decreases down to atmospheric pressure; hence, an engineer will readily perceive that, by a suitable arrangement of valves and pipes he may beneficially employ part of the power of the engine for transferring the air from the traction-pipe back into the reservoir. In using this part of our invention, a suitable slide, or other valve, must be caused to close the end of the section of the tractionpipe as the piston leaves it, so that the air may be closed from passing beyond the section if the traction-pipe end there, but where the one section of the traction-pipe is continued by another section, only having a slide, or flap valve between them, then the closing of the next of the transverse valves will be sufficient. This means of working atmospheric railways, like those heretofore proposed, may be used on double or single lines; but we believe that single lines will be generally found sufficient; in which case, the working of the valves and the engines,

and the general working of the railway, will be greatly facilitated by the use of the electric telegraph; and where single lines of railway are preferred, then at stations, where trains are to pass each other, the lines will require to be double, in which cases very little delay will take place between the passing of trains from and to a section of the traction-pipe in opposite ways; for no sooner is one train gone, than at that instant the piston of the other train may enter the same section of traction-pipe, it being understood that, when this instantaneous passing in opposite ways of two trains be desired, then the benefit of using the third part of our invention in those sections of the pipe, will, for the time being, be dispensed with.” •

ON THE ADVANTAGES OF THE ATMOSPHERIC STATIONARY SYSTEM OF TRACTION AS COMPARED WITH THE LOCOMOTIVE. BY PETER W. BARLOW, ESQ., C. E. [Abstract of a Paper read before the Institution of Civil Engineers, February 25, 1845.] The author having been required to examine and to report upon the question of the comparative advantages of the atmospheric railway system, with a view to the propriety of its application to the Tunbridge Wells branch of the South Eastern Railway, and as there appeared to him several results from the use of this mode of traction, which had not apparently been previously noticed, he was induced to lay his investigations on the subject before the Institution, in the hope that they might be found to contain some useful information, although the little time he was enabled to devote to it, prevented his making any very detailed calculations.

In the application of stationary power to traction on a railway, by means of the exhaustion of air in a pipe, several of the inconveniences of the present mode of traction by a rope, are avoided, and the great difficulty of rendering the pipe air-tight, has been in a great measure overcome by the ingenuity and mechanical skill of the inventors. It is but fair to assume, in comparing the atmospheric system with traction by locomotive power, that still further improvements will be made in those features of the invention which relate to the mechanical construction.

Whatever may be the result of the comparison, in a purely mechanical point of view, that is to say, in a comparison of the cheapest and quickest mode of moving certain weights over a given distance, it must be considered, whether the power required on railways generally, is of that uniform character which admits of mathematical com

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putation, and whether, by the adoption of the atmospheric or any stationary power, certain rules and regulations are enforced, which are inconsistent with the ordinary traffic on a railway.

On lines like the Greenwich or the Blackwall Railways, when the traffic is perfectly uniform, consisting of a certain number of trains daily, at stated intervals, the power admits of a mathematical computation; but on railways generally, the power required is liable to considerable irregularities; and a power, which is practically restricted to carrying between certain given points only and at certain intervals, would lead to great inconvenience.

On all railways not carried upon arches, a great deal of work is requisite for maintenance of the road and the works, which must be entirely intermediate traffic, consisting of bringing ballast and other materials to repair the road and works, the removal of slips, &c., and one or more engines are constantly employed for these purposes on all the principal railways. There is also traffic of coal and lime at sidings, to various intermediate points on all railways: and at the principal stations, much manual labour is saved by the locomotive in moving goods, trucks, carriages, &c., from the siding to the main line. The power for this purpose cannot be efficiently applied by the atmospheric system, because it does not admit of traction between intermediate points, except at a cost and inconvenience which would be inconsistent with practice, and must prove an objèction to the use of atmospheric or any stationary power. This can be only surmounted by having locomotive engines for this purpose, and it involves a small and consequently expensive locomotive establishment, renders necessary locomotive gradients, and consequently prevents the saving which, it is contended, can be made in the construction of the atmospheric railway, by the use of steeper gradients.

Another practical inconvenience, which will be found in the atmospheric railway, is, that the journey cannot be repeated on a length of pipe until after a given interval, which is necessary for forming the vacuum; the power is, therefore, not always at instant command, and the transmission of special trains and expresses is materially interfered with.

The same objection will also, upon consideration, be found frequently to interfere with the general traffic, at the stations where the up and down trains pass, as it is evident both must wait until the air is exhausted from within the pipes to the next engines. The length of this time will depend upon the extent of the pipe and the power of the

engine; but it could not be less than 6 minutes, which is a serious loss of time to occur at the passing of every train, and on a long line, with trains every half hour, would reduce the average speed to 20 miles per hour. If the length of pipe to each engine was extended to 10 miles, as has been proposed, this loss of time would be more serious, and would amount to 20 minutes or half an hour, unless very powerful engines were used.

Another important objection to the atmospheric railway, is that the traffic is dependent upon keeping air-tight a great length of pipe, and upon the perfect order of a great number of engines; in fact, it depends upon the perfect order of an extensive, delicate, and complicated machine, composed of an infinite number of parts, the failure of any one of which would render the whole machine useless; and it must be evident, to any person practically acquainted with the maintenance of a railway, that the machinery of such an engine will be liable to frequent interruptions, from causes which it would be impossible to control.

The subsidence and slips of embankments and cuttings do not now interfere with the traffic of a railway, unless they are of great extent; because a line of rails, if injured, is soon replaced, in situations where the continuity of the pipe would be destroyed, and the traffic would be intercepted. Slips, which are not of sufficient magnitude to excite public attention, and which, in fact, do not interfere with the trains, are of more frequent occurrence, in wet weather, than is supposed, and will render the maintenance of a pipe, in addition to the rails, not only very difficult and expensive, but in many cases impracticable.

There will also be another source of danger, from increased liability of the carriages to run off the rails of the atmospheric railway. The locomotive, from its great weight, runs over and destroys any impediment which may be on the rails, but which would throw off a carriage. Such impediments, it may be supposed, need not exist; but in spite of every precaution, they are found, in practice, to do so to a great extent. On many railways, cattle are continually run over; tools or planks are frequently left by the workmen on the rails; such things are also frequently put on designedly; stones and flints also fall from the sides of the cuttings upon the rails. Such impediments are thrown on one side, crushed, or run over by the locomotive, but a carriage would be thrown off by them; and by a very small impediment, the traffic on the atmospheric line would be stopped, and serious injury would, in all probability, be done to the

pipe and machinery, which would require a considerable time to repair.

These objections to the system may be considered frivolous by those unacquainted with the actual maintenance of a railway; but the uncertain medium by which the traffic is maintained on the atmospheric railway will be fatal to its use for any traffic of importance. A person carelessly or maliciously disposed may, at any time, totally destroy the connexion of the power; and it is well known how frequently this has been attempted on existing railways, and it would be oftener successful, but that the attempts fail from the great weight of the locomotive.

These remarks refer to long lines of railway but the objections above stated do not apply to short lines like the Greenwich and Blackwall, constructed on arches, and in such situations, unless frequent intermediate stations are required, the system has undoubtedly advantages from its superior quiet and speed, with light trains; and, as will be seen by the following investigation, it will also, in such cases be comparatively more economical.

The question of the comparative cost of haulage, by the stationary and the locomotive systems, was thoroughly investigated, when the locomotive engine was first introduced. It will be seen, that in railways, where the trains are not numerous, the stationary power, in whatever way applied, is worked under a great disadvantage, from the small portion of time which is actually occupied in the passage of the trains on the length assigned to each stationary engine.

The irregularity of traffic on a long line of railway, will be illustrated by the occasional necessity of removing large bodies of troops. The daily average traffic of several of the principal lines, very little exceeds the number of a full regiment of infantry; but it may be necessary to convey several regiments on the same day, and even at the same time; therefore to meet such a contingency, it is evident, the power must be so great as to work at other times at great disadvantage.

The actual lost power, in the locomotive engine, although considerable, is not so much as might be expected, the greater portion of loss being in the power required to convey its own weight and that of the tender; consequently, the amount of lost power is very much greater on lines with bad gradients, than on those with favourable ones, and on steep gradients the atmospheric principle is comparatively more advantageous, in a mechanical point of view.

It is necessary, however, to observe, that a very common error exists in supposing that steep gradients are attended with com

paratively little inconvenience on the atmospheric railway. They must of course render necessary the additional power due to the increased traction, which makes an important difference both in the first cost and in the working expenses. Thus in the gra dient on an incline of 1 in 50, the sectional area of the pipe and the power of the stationary engines will be required to be four times that which is necessary on a level railway, and the working expenses will be increased in the same proportion; in fact, the cost of the apparatus, to give the requisite tractive power on a single line of railway of the above inclinations, would exceed the total cost of a double line, constructed for locomotive power. This result is very much at variance with the statements made in the first instance by the inventors, as to the great saving of cost in the first construction.

The result that steep inclines are better worked by the atmospheric system, has been evidently arrived at without considering the cost of construction, which becomes practically a very important question in the atmospheric stationary power, from the large section of pipe that is necessary. The outlay, as well as the working expenses, will be increased nearly in proportion to the sectional area of the pipe, from the circumstance, that the pressure is limited to that of the atmosphere, and this limitation of the pressure is a great practical objection to the atmospheric system; in fact, in comparing the atmospheric system with traction by the rope, the latter will be found to have much the advantage with steep gradients, and experience will show, that the atmospheric system is practically much better adapted to level lines of railway, than to those with steep gradients, which, if exceeding the inclination adapted to locomotive power, will be worked more advantageously by the rope. There are, however, few instances in which the inclines are required to be so steep, that the locomotive cannot be more advantageously applied; and the fact of the abandonment of stationary power for the locomotive, on the inclines on the Manchester and Leeds railway, and on the Edinburgh and Glasgow (the inclination of both being greater than 1 in 50) as well as in other cases, is not only a proof of the improved capability of the locomotive engine, but of the inconvenience found in practice from stationary power.

The objection which will interfere most sensibly with the adoption of the atmospheric system, is the necessary outlay in the engines and the pipe, and this seems to have been lost sight of in the calculations of the economy of working, which have been made by its advocates.

Referring to the calculations of the cost

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of working on the London and Birmingham Railway; to lay down the apparatus of a double line, with a pipe of the required area, would not be less than £10,000 per mile, or a total cost of £1,120,000; and the interest of this sum, at 5 per cent., will be £56,000, or £500 per mile, or a sum very nearly equal to the actual cost of working that railway by locomotive power, and exceeding the average cost of most of the long lines. In fact there is no doubt that respectable contractors could be found, who would supply locomotive power, and work any railway, for the interest of the sum which would be expended, in laying down the atmospheric apparatus.

If the interest on the necessary additional outlay is equal to the cost of working by locomotive, it is evident that it cannot be applied to main lines already executed, even if the working expenses were entirely saved.

It has been stated, that an economy may be effected in the cost of the construction of the tunnels and the bridges, by avoiding the use of the engine; but this is erroneous, as the dimensions are governed by the size of the goods' trains, the carriages and the trucks, and not by the engine.

A calculation has been made, showing a reduced cost of maintenance of the permanent road; but experience has shown, that in this department any calculation must be so completely vague, as to be totally without practical utility.

The chief cost of maintenance of way on ordinary lines, is from the settlement of the embankments; and on new lines it is sometimes extremely difficult to prevent an interruption of the traffic, during the winter, from the sudden and irregular settlement which a few hours may produce. On recently made embankments, it would be found extremely difficult to keep in order the road with the atmospheric pipe, and it could certainly only be done at a very increased cost.

It may be argued, that as the weight of the engine running over the road is avoided, less repair will be necessary. In cuttings, some saving might be expected from this cause, if there was no pipe in addition, but with this addition, and on a line with the ordinary proportion of embankment, it is to be apprehended that the cost of maintenance will become a serious expense.

From these observations, the following general results have been arrived at :

1st. That the situations best adapted for the application of the atmospheric principle, are on lines where the trains are required to be numerous. This must generally occur near towns, and in such cases, additional advantages would be derived from the absence of the noise of either the locomotive