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working the plant. The initial outlay for water-power would perhaps be greater than for a steam plant, but the cost of working would be cheaper. The longest of the tunnels required to pierce the pass with a workable grade could be constructed in about five years, and the shorter tunnels in a proportionally less time, and in the case of the latter of a length of 3J miles or less the work could be expedited by the use of shafts. This would, however, increase the cost of the tunnel, owing to the extra handling of the material, the cost of the shafts, and the cost of the special hoisting-plant, &c, required. Under unfavourable conditions there may be serious difficulties in working any of the proposed long tunnels, except the 2J-mile one, as all of them would bo on the maximum grade for their whole length; and at all times there would be more or less discomfort to the train crew and passengers. With a high wind blowing west to east it is possible that an up-grade current of air would be induced in the tunnel sufficiently strong to carry all the smoke and steam along with the train, and render the train crew unfit for work. Serious accidents have resulted from such a cause in tunnels on the same grades, but of much shorter length than will be necessary at Arthur's Pass. In order to abate the smoke nuisance and minimise the risk of accident therefrom, it would be necessary to employ an effective system of artificial ventilation, or burn liquid fuel in the locomotives, or perhaps to combine both methods; but all difficulties of this nature could be avoided by the adoption of electric traction on the Otira-Bealey section. The system of artificial ventilation that would likely be most suitable is that of Saccardo, now employed on the Italian railways and on the St. Gothard tunnel through the Alps, and which in all cases appears to give great satisfaction. On this system air is injected into the upper end of the tunnel through an annular opening, in sufficient quantities and under such a pressure as to induce a powerful down-grade current under all conditions when the train is travelling up grade in the tunnel. The drivers and stokers are always in a current of pure air and kept fit for duty, thus insuring the arrival of the train at the upper end of the tunnel. The tunnels on the l-in-37, l-in-40, and l-in-44 grades could be worked by the Saccardo system of ventilation, but there is no doubt passengers would sometimes be inconvenienced by the smoke, as at a speed of, say, ten miles an hour the train would be from twenty to thirty-seven minutes in the tunnel. Purely passenger trains could be run at higher speeds, but the passenger traffic is not likely to justify the running of passenger trains. The installation of the system would cost about £10,000, but this sum might be reduced by the use of some of the construction plant for ventilation ; the cost of working would also be considerable. To give the system every chance of success, it will be prudent to make the tunnel of a larger section than the standard New Zealand section ; this will increase the cost considerably. Ventilation of a long tunnel is also necessary to enable the surfacemen to carry on their work. A cheap and easy way of minimising the smoke nuisance in tunnels is to use liquid fuel on the locomotives when passing through the tunnels. This has been done with great success in the case of the Arlberg tunnel through the Alps, in which there is a l-in-66 grade, four miles long. Liquid fuel has also been used with success in Circassian tunnels, one of which, the Suram, is two miles and a half long, with l-in-55 grade ; and in Peru, on the Oroya line, a tunnel three-quarters of a mile long, on a l-in-27 grade, is now worked satisfactorily with liquid fuel, while it was only worked with great difficulty when coal was used. One pound of liquid fuel such as is used in locomotives is said to be equal to 1-JTb., or even 21b., of best coal, and the cost of working the locomotives with it is less than with coal in the case of the Arlberg tunnel; but this will depend on the relative prices of coal and oil at the place where it has to be used. As liquid fuel is not yet a natural product of New Zealand, the question of supply has to be considered carefully before deciding on adopting any scheme necessitating its use. There is also the possibility of the supply being cut off in war time; but in that case the liquid by-products of gasworks would form an excellent substitute. With liquid fuel much more perfect combustion is obtainable than with coal, and the result is much less pollution of the air in a tunnel. Locomotives can be fitted with injectors, oil-tanks, &c, to enable them to use oil when required, at a small cost —say, £60 to £70 each—and an experiment on one of the New Zealand steep-grade lines would be valuable. To work the Otira-Bealey section with liquid fuel it would be necessary to provide storage-tanks at suitable places, and some special tank trucks would be required. Suitable oil is, or was, obtainable in England for £2 per ton, and if supplies could be obtained, say, from the Borneo oilfields at about this rate it seems as if liquid fuel could be used with advantage in working any tunnel that might be constructed at Arthur's Pass. It is probable that with liquid fuel the wasting of the rails in a tunnel would be much less than if coal were used, as the percentage of sulphur in the coal likely to be used on the Midland Eailway would cause excessive wasting, as is found to be the case in most tunnels. If liquid fuel was used in combination with good artificial ventilation there is every reason to expect that a long tunnel could be worked with little or no difficulty, and the expense of the combined installation would not likely be great—say, £15,000. The most perfect method of traction for the long tunnel on the l-in-37 grade would, there is no doubt, be found to be electric traction. The Commission that reported finally on the Simplon tunnel scheme before the construction commenced recommended the use of electric locomotives for working the tunnel, which is 12 miles long. On the Baltimore-Ohio Eailway electric locomotives 86 tons weight are in use. Passenger trains 500 tons in weight are drawn through a tunnel about one mile and a quarter long, at a speed of fifty to sixty miles per hour, and goods trains weighing as much as 1,600 tons are hauled at speeds up to twelve miles per hour; the grade is lin 125. A much less powerful locomotive than is required to work the Baltimore tunnel would be sufficient for the Arthur's Pass tunnel, and could easily be made, allowing for the lesser width of gauge, to take up the full train-loads of heavy locomotives on the l-in-60 grades at speeds from, say, ten to twelve miles an hour. A smaller section of tunnel could safely be adopted for electric traction, but the cost of the electric locomotives, power-station, and conductors would be

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