Part 5
I guaranteed that the locomotive referred to should take a load equal to its own weight up a gradient of 1 in 10 a quarter of a mile long, which then was, in parts, as steep as 1 in 9, with a short curve of half-a-chain radius at the severest part. This was satisfactorily accomplished. The day being dry, I was requested to ascertain what was the maximum load that could be hauled. On reaching four tons, when the start had to be made on a less gradient, the engine barely struggled up, and this was evidently all it could do. When full up with coal and water it weighed at that time 3 tons 6 cwt. During the experiment, however, there were but 3 tons 2 cwt. on the three axles, all of which were coupled. The boiler pressure was 145 lbs. exactly, and, the gross weight of engine and train being 7 tons 2 cwt., the gravity resistance on the gradient of 1 in 10 was equal to 14.2 cwt. The weight of 3 tons 2 cwt. available for adhesion, reduced by a tenth part, which the gradient converts into gravity resistance, was equal to 56 cwt. Thus, without reckoning the curve friction of the whole train and the journal friction of the wagons, both uncertain quantities, the proportion of developed tractive power to load was as 1 to 3.9. This result confirms the probability of the truth of the above assertion. Assuming its correctness, which appears beyond doubt, what is the explanation of increased proportionate adhesion with a decreased weight on the driven axles? The reduced diameter of wheel in the smaller engines might seem to offer a solution of the problem. Experience, however, goes to prove that, if there is any difference, a larger wheel has, with equal insistent weights, a better grip of the rail than a small one. I am of opinion that the weight is directly responsible for the difference. A wheel rests upon a rail on one point, or possibly on a transverse line of which the length is equal to the width of the rail. With a small insistent weight the molecules of the wheel and rail interlock without injury, and adhesion, on the principle of an infinitesimal rack and pinion, is the result. As the weight is increased on the fine bearing area, the molecules become disturbed, and fail to offer so firm a fulcrum. Ultimately they become displaced, and move as rollers between the two surfaces, materially reducing the adhesion. If this theory be the correct one, as is not improbable, the graduated reduction in the adhesion would be accounted for.
That the rolling wheel and rail do actually interlock was demonstrated by Sir Douglas Galton in his experiments on the retarding power of brakes, when he pointed out that, on a wheel becoming skidded, the rack and pinion motion was converted into a series of jumps of the wheel across the microscopic teeth of the rack, with a consequent reduction in adhesion proportionate to the sliding speed. In confirmation of this statement I detailed, during the meeting of the British Association at Sheffield, an experiment I made by reversing a locomotive so as to skid the wheels, and ultimately to cause them to revolve in a contrary direction, while descending an incline. With skidded wheels the descent was at a certain speed with backward revolution of the wheels the speed increased rapidly, the effect of the reversal being to cause the wheel to slip over the rail at a speed greater than that at which the engine was moving, thus showing that Sir Douglas Galton’s theory of the adhesion diminishing in proportion to the extent of departure from the interlocking or rolling motion of the wheel on the rail remained consistent even beyond sliding contact, and disposing of the old theory that the loss of adhesion with a skidded wheel was due to the creation of a polished point of contact on the wheel.
Another somewhat curious point in connection with adhesion is the slip of the driving wheels, which is naturally in the direction of causing a greater number of revolutions of the wheels than would be due to the length of rail travelled over. Occasionally, however, I have, in experimenting, noticed that fewer revolutions are made than would suffice to travel the distance as measured on a centre line between the rails. That is, the wheels slipped forward instead of back. This freak is probably due to the outer wheel on a curve slipping forward when, owing to considerable superelevation and a low speed, the inner wheel is the more heavily weighted, the distance then travelled being the reduced length of the inner rail.
I now proceed to explain the basis of calculation of the net loads hauled on various gradients, as appended to particulars of each locomotive described in Section V. The resistance on the level consists of journal friction, tire friction, and locomotive internal friction. Tire friction is practically nil, except on curves and in strong side winds. Journal friction I find, in the case of my small rolling stock, to be covered by an allowance of 10 lbs. per ton. Owing to the numerous curves another 10 lbs. per ton must be added to cover tire friction. A tractive power of 20 lbs. per ton proves quite sufficient to keep the train in motion on the level. It is not, however, enough to start the train on a curve, nor to overcome the inertia due to journal friction when, as on an incline, there is no slack between the wagons, and the whole train must be started at once. After considerable experience I find it necessary to add a further 20 lbs. per ton to the required tractive power. A total of 40 lbs. per ton is thus allowed as a good working equivalent of the frictional resistance of the train.
The friction of the locomotive is a much more complicated question. There seems very little information available on this point. It has been said, in the case of full sized engines, to absorb thirty per cent. of the tractive power, but this is a vague estimate, out of all reason excessive, unless it be intended to include gravity resistance on a steep incline. It is desirable to consider the nature of the various causes of resistance to motion separately. Viewed as a carriage only, the journal and tire friction of the locomotive may be taken at the same amount per ton of its weight as in the case of the trains, namely, 40 lbs. The additional resistance due to friction of the moving parts of the mechanism cannot be calculated as a constant. If the engine is developing but a small portion of its power, the amount will be small; when loaded to its full capacity there will be a large increase of internal resistance, varying, however, in proportion to the accuracy with which it is put together, and the stiffness of the framing.
Such experiments as I have made show clearly that, when exerting approximately its full power, the total frictional resistance of the engine does not exceed 100 lbs. per ton, and when running light is much less, but in what proportion less I have as yet failed to ascertain satisfactorily. Of this 100 lbs. per ton, from 20 to 40 lbs. is due to journal and tire friction, leaving from 60 lbs. to 80 lbs. per ton as the deduction for internal friction.
I thus conclude that an allowance of 40 lbs. per ton for train resistance, and 100 lbs. per ton for engine resistance, is a basis for calculating the tractive power required on the level that is sufficient under all possible narrow-gauge conditions. In the case of gradients there must, of course, be added the gravity resistance of the engine and train, which is, on a gradient of 1 in 100, one-100th of the gross weight; on a gradient of 1 in 50, one-50th, and so on.
In calculating the tractive power of the engine, the effective pressure in the cylinders may be reckoned at fully nine-tenths of the boiler pressure, on account of the low piston speed.
The above particulars are not to be taken as representative of what can be got out of a narrow-gauge engine in a few isolated experiments only, but of what is well within the compass of daily work.
IX. REMARKS ON NARROW GAUGE RAILWAYS.
UP to this point I have merely detailed the particulars of the construction of my experimental railway and of the line at Eaton, giving at the same time the reasons that have led me to adopt certain methods and designs. I now propose, in conclusion, to offer a few remarks upon the application, in this country and abroad, of small railways of 2 ft. gauge and under to do work at present done by means of horses and carts.
The cases in which such lines can be profitably applied may be classed under two heads; the one, where, in a country possessing ports or a system of railways, large establishments, private, public, or industrial, might be connected therewith by a narrow gauge line so as to reduce the cost of transport below that which has to be paid for haulage by animal power on roads; the other, when no roads worthy of the name are available, and the choice is a light railway or nothing. The chief condition of success in both cases is a sufficient traffic between two or more definite points. Military railways, however, must be regarded from a somewhat different standpoint, as the object here is to supply a movable centre as expeditiously as possible with the vast commissariat requirements of an army rather than to study economy. It is not my intention to enter into the pros and cons of small railways for war purposes. Suffice it to say that some countries are ahead of us in the matter, which is one that has, in England, been allowed to drop rather into the background.
Returning to the consideration of cases where a fairly large traffic has to be delivered to a port or railway system, the first question that arises is that of transhipment. Material of any kind can be as effectively delivered on ship-board by narrow gauge railway wagons as by horses and carts, if not better. In reckoning up the cost of transhipment from small wagons on to a railway system—no great matter with proper appliances—it must not be lost sight of that, even if a branch of standard gauge were constructed to many establishments, the large wagons cannot, as a rule, be got up to the point where the material lies, and a preliminary transference in barrows or carts is necessary. With the little wagons it is usually possible to get right up to the place and to load direct, in which case there is clearly no additional expense incurred. It is, further, often forgotten that there is on the standard railways endless transhipment for the sake of economical transport, in no way connected with a break of gauge.
Again, a small line can be carried round curves, up gradients, and through confined premises, where a wider line would be inadmissible. In many places the unsightliness of the standard gauge would be objected to, nor can such a line be made very light if it has to carry, as it must, the 7 or 8 tons per axle of a full sized coal wagon (see Appendix A).
The narrow gauge has also the advantage in first cost, and by bringing the small wagons on to a level with the floors of the large ones, or, in the case of minerals, by erecting a simple shoot, the transhipment difficulty may be reduced to a minimum.
It is not well to have gradients steeper than 1 in 40 where avoidable, as difficulty will be experienced in slippery weather; but it is quite possible with suitable engines to work inclines of moderate length, as steep as 1 in 12. The diminution of the power of the locomotive on gradients is also a matter for consideration, the importance of which will be clear when it is stated that if an engine will haul, as it should, in addition to itself, ten times its own weight on the level, it will haul, speaking roughly, only four times its weight up 1 in 50, twice its weight up 1 in 25, and once its weight up 1 in 12. More work can be done if adhesion does not fail, but the above is an approximate working average.
The speed on small lines is not generally a matter of much moment, owing to their usually moderate length. A locomotive that is sufficiently powerful to start a given load, will without difficulty get it along at from 8 to 10 miles an hour. It has occurred to me that a very fair approximation to the reasonable running speed of which any gauge is capable is to be found in estimating that the speed of passenger trains is equal to as many miles per hour as the gauge is inches wide, and, for goods trains, to half that amount.
The permanent way should be made a thoroughly sound job, as it will then cost but little for repairs. Particulars of what is recommended will be found in Sections III. and IV. I am no advocate of portable railways, which may be well enough for hand trains, or even for horse traction, but a locomotive requires a solid and clean road if it is to work to advantage.
It is often possible to carry a narrow gauge railway by the roadside or, as at Eaton, over pasture lands without the necessity of fencing the line in. Fences can be crossed as described in Sections III. and IV., so long as arable land is avoided. Where the route is not wholly the property of the projector of the railway, the requisite way-leave may frequently be leased by paying an annual acknowledgment of from 3d. to 6d. per yard run.
It now remains to show what traffic is required in order that a line of this description may repay the outlay upon it. This may best be effected by drawing a comparison between the cost of locomotive traction on rails and horse traction on roads. The cost of loading and unloading will not be included, as these are the same in both cases. (See also Section IV.)
Taking the minimum distance apart of two points, between which haulage may be supposed to be required, as one mile, the smallest and cheapest gauge as 15 in., and allowing 2,000 yds. to the mile so as to include the necessary sidings, the cost of the line will be as follows:—
2,000 yds. of 16 lbs. steel rails, cast-iron sleepers, £650 ballast, and laying Fence bridges, field crossings, fencing, and other £200 structural works; but exclusive of river bridges, tunnels, or other costly requirements Earthwork, if an approximately surface line ... say £250 One 4½ in. cylinder four-wheeled locomotive £400 12 wagons to hold 1 cube yd., at £12 each £144 Extras ... say £156 Cost of 1 mile of line, equipped complete £1,800
If laid with pitch pine sleepers a reduction of about £100 per mile would be effected, the cost of renewal being correspondingly increased.
The engine would be capable of hauling a gross load, exclusive of its own weight, of 12 tons up a gradient of 1 in 50, which may be taken as a fair ruling gradient for a surface line. This would be equal to an average paying load of about 8 tons; so that, supposing the engine to make one trip per hour, about 60 tons would be moved per day; although, with a double set of wagons and men, 100 tons would easily be handled.
If the engine worked two days a week, or say 100 days per annum, it would have hauled 6,000 tons one mile in the year. A less load hauled on the return journeys need not be taken into account, as this would make no difference in the comparison, such work being practically done without extra cost in both cases.
The cost of the line per annum would be as follows:—
Interest on £1,800 at 4 per cent. £72 Driver and boy, who would keep the rolling stock and line in £100 order Fuel, oil, stores, and sundries, at 5s. per day £25 Renewal of permanent way and rolling stock at 15 years life £80 on £1,200 Cost of moving 6,000 tons one mile £277
This is equal to about 11d. per ton. Now the same haulage by horses and carts in Great Britain would usually cost about 1s. 3d. per ton, and in this case there is the advantage of being able to haul, if necessary, in other directions if required, which would somewhat reduce the financial advantage of the railway, but still leave it a distinct superiority.
It is probable that a traffic of 5,000 tons annually over a mile of line is the smallest amount that would repay the construction of a narrow gauge railway, for the estimate has been based upon the narrowest line which can profitably be employed. If the line were longer, the balance in its favour would be greater. This would also be the case if the traffic were greater, and with the maximum amount which the line, using only one, but a larger engine, could accommodate, say 40,000 tons, the concern would be very profitable, for the extra charge for renewals would not be heavy, and the cost per ton carried would be reduced to about 5d. or 6d.
No allowance has been made for way leaves or purchase of land. Should there be outlay under these heads, the cost of transport would be increased accordingly.
In concluding these comparisons, in which it may be thought that the railway is shown in a less attractive light than might have been expected from an enthusiast, I may explain that I am no advocate of ill considered schemes, planned without proper knowledge, cheaply constructed, and carelessly worked. My figures represent thoroughly sound and serviceable plant, kept in good repair. If it is not worth while to go to such expense, then it is not worth while to construct a railway at all. I have been fortunate enough to work my line for twenty years without the slightest injury to a single person of the many thousands that have been carried as invited guests for pleasure, as visitors interested in my experiments, or as workmen on the premises. None of the rolling stock has sustained more than the most trivial damage; and derailments, beyond an occasional mishap in shunting, are unknown. The working of the Eaton line has been equally satisfactory. This immunity from accident I attribute entirely to proper care having been taken to construct every part, not only of the best materials and workmanship, but also with a careful eye to the fitness of each detail for the purpose it has to serve.
That there are many openings for lines of 2 ft. gauge and under, is beyond dispute. But while, already, this mode of transport is largely made use of abroad and in our colonies, a deeply rooted prejudice has hitherto prevented it from gaining a footing in England and Scotland.
Admirable articles pointing out the advantages of light railways have appeared from time to time in the daily press with little or no effect. It is one of the strangest anomalies in the progress of civilisation in this country that Great Britain almost wholly refused till lately to countenance such lines. The reasons for this obstinacy are not readily discoverable. Probably the innate conservatism of every Englishman—for there exists here no such thing as liberalism out of the region of politics—has been the principal factor in determining this course of inaction.
Even now that the Light Railway Act has passed, there is little or no movement in the direction of making small lines such as I refer to, and not much in respect of larger ones. Whether, in the future, private individuals will, in their own interest and in that of their neighbours and dependents, lay out money in this way, it is impossible to foresee. But undoubtedly there are many openings for such installations, particularly on large estates, where the possession of the land gives the owner a free hand.
X. APPENDIX
A
THE following letter, which appeared in _The Times_ two years ago, is here reprinted as bearing on various points connected with narrow-gauge railways. Special attention is directed to what is advanced under the third head.
LIGHT RAILWAYS. _TO THE EDITOR OF_ “_THE TIMES_.”
Sir,—The movement in favour of secondary railways has evoked from your numerous correspondents widely divergent views. This want of accord is more apparent than real, and it would facilitate the proceedings of the approaching conference {46} if conflicting opinions could be partially reconciled beforehand.
The causes to which these differences are due may be summarized under three heads:—
1. The absence of a defined terminology of the distinctive kinds of railways.
2. The failure to appreciate that a scheme which is good for one locality is not of necessity the best for all.
3. The apparently meagre acquaintance on the part of those who state their views with the practical working of any but the standard railways of the country.
Under the first head, some confusion has arisen in consequence of the application of the term “light railway” now to lines of the standard gauge only, and again to narrow-gauge lines also. Similarly with other expressions. It may be pointed out that the term “light railway” is properly applicable and should be confined to a line of standard gauge, of which the entire construction is lighter, cheaper, and simpler than is obligatory where weighty engines, heavy traffic, and high speeds are dealt with. Any line of less than the standard, gauge is correctly described as a “narrow-gauge railway,” and such lines, when not of a permanent character, come under the title, simply, of “portable railways,” for these are invaribly of less than the normal width. The term “tramway” should be restricted to its modern meaning of a line laid in the metalled or paved surface of a road or street. Finally, the not unfamiliar appellation of “secondary railways” might be fitly adopted as generally descriptive of all lines not amenable to the standard railway regulations of the Board of Trade. It would be well that the conference should pronounce on these points.
In regard to the second head, needless controversy is engendered by attempting to assume that, because a light railway is right here, therefore a narrow-gauge railway is wrong there, or vice versa. In estimating the transport requirements of any particular locality, if connection is to be made with the railway system, the applicability of a light railway, as above defined, should first be considered. By its adoption the use of existing rolling-stock is secured, transhipment is avoided, and the line can be subsequently and without difficulty transformed, if necessary, into a railway of standard construction—advantages for which much may be sacrificed. But as it would be almost invariably essential to build a light railway of sufficient strength to carry the 15 tons gross weight of a standard coal wagon, the permanent way would be of a somewhat costly character, and, in the case of severe gradients, considerable difficulty would arise in providing suitable locomotive power.
Where the impediments in the way of a light railway branch are insuperable, or where the proposed line has no connexion with the railway system, the advantages of a narrow-gauge railway may properly be weighed—such as the smaller width occupied, the sharper curves admissible, the lighter, cheaper, and more easily-handled permanent way and rolling-stock, the absence of much of the unsightliness of a line of standard gauge, the ease with which, in the ease of gauges under 2 ft., the rails can be laid among and into existing buildings, and, lastly, the convenience of being able to load and unload small wagons at the exact point required without the intervention of carts or barrows.