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.