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grade and empties up 8-per-eent. In addition, the trolly-line was an extension of the feed-line for some ten or twelve mining-machines, in consequence of which the voltage varied from 110 to 200, and the battery would either feed back into the line or throw the circuit-breaker. In order to prevent the latter it was so adjusted that it would not fly out, and the battery was virtually short-circuited a large number of times each day without any bad effect. With this condition of affairs it was impossible to hold sufficient current in the battery to do the desired amount of room-work, and it became necessary to stop a total of about thirty minutes each day for renewals. It must be remembered that this work was under the supervision of a mine-foreman unacquainted with storage-batteries. Having gone to such extremes in the use of this locomotive, it was suggested that a new and independent feed-line would be a great improvement; it was installed with marvellous results. The voltage became constant, and the battery often discharged for a short time at three times its rated capacity; yet the work has been ideal, and after almost three months' service there is no appreciable wear on the battery. It produces a tractive effort up to the point of adhesion of the locomotive when working on storage, and the regular work is to take seventeen empties weighing 60,0001b., including locomotive, from side-track up a short 1-per-eent. grade, then down a 4-per-cent. to a level, from which place it starts to distribute in rooms having a maximum of 8 per cent, in favour of loads. After distribution it proceeds to collect the loads in trips of two cars each, on account of the 4-per-cent. grade against loads on heading, and deliver them to the side-track while working on trolly. In this manner this one locomotive is capable of delivering to this side-track, over an average round-trip haul of 4,000 ft., two hundred loaded wagons daily direct from face of working, which is the work, under existing conditions, of twelve mules and eight drivers. It is the intention to place a night force, and if sufficiently large the saving will be the care of twenty-four mules and time of twelve men, or an amount equal to $8,000 annually. This same company has placed an order for six more of the same class of locomotives, and are considering the matter of constructing heavier ones of the same kind to take the place of steamlocomotives now in use, but which are very injurious to both the ventilation of the mine and the timber-work. In general, it costs from 6 to 10 cents per ton to deliver coal from face of workings to shaft, slope, or tipple, where the haul is one mile, and the tracks approximately level; yet I have in mind three mines which at present haul from parting with the trolly system, the miner delivering from face of room, making an average round trip of 9,000 ft., at a total cost of 1 cent per ton. These mines have never had a mule in them, and it would be almost an impossibility to introduce them, for the reason that the seam is of such thickness that the clearance between tie and roof is only about 4 ft. Since the advent of the electric mining-locomotive there has been a change in the mine-wagons universally used. Formerly it was customary to find as much as 60 lb. per ton car-resistance on the level, while at present it is as low as 15 lb. In dimensioning mining-locomotives it is customary to make the weight from six to eight times the necessary tractive effort dependent entirely on the nature of the work. If the work is constant and a maximum, then the weight would be only six times the torque of the motors, while if the work is intermittent, with a short-time maximum tractive effort, then the factor would be eight. For maximum continuous work it is necessary to have a grade such that the efforts to haul the same number of empty wagons as loaded are equal. With the car-resistance considered 1 per cent., and the loaded cars weighing three times as much as the empties, this is found to be onehalf of 1 per cent. The most critical point in the designing of mining-locomotives is to make the limiting dimensions a minimum. The demands for various dimensions are wonderful. The headings in mines are never of more generous proportions than really necessary, and all clearances a minimum. The minimum dimensions for mining-locomotives are as small as 2 ft. for wheel-base, 8 ft. for length over all, and 3 ft. width. Scarcely two orders carry the same dimensions, and it is impossible to have any kind of a standard. In consequence of this it is necessary to have a great variety of motors suitable for gauges as narrow as 18 in., and for wheels as small as 20 in. in* diameter. With such a variety, it becomes possible to construct a locomotive weighing 40,000 lb. on 3 ft. gauge, having the width over all 62 in., height 35 in., and length 12 ft. In such construction it is necessary to have the most modern form of motors, and the most rigid mechanic construction. The motors now used are of the best possible construction and efficiency. They are of the slow-speed street-car type, six to eight miles per hour, winding, and range in size from 4- to 50-horse power. It is customary to use the rheostatic type of controller for mining-locomotives on account of its small dimensions and apparent efficiency for this class of work, but it is doubtless but a short time until a very compact form of series-parallel type will be devised. On account of the use of this rheostatic controller it becomes necessary to provide for large diverter-capacity, and, since the locomotive is designed for the maximum tractive effort, it is hardly ever possible to run without resistance, and hence a large amount of current must be dispersed with the consequent heating. The demands for mining-locomotives come from all quarters of the globe, thus showing that engineers in every section are awake to the fact that modern mechanic appliances are an absolute necessity in the art of mining. In order that a comparison may be made between a mule and a locomotive, I have deduced from practical observation that the former as well as the latter can produce a tractive effort of onefifth its weight for a maximum, and one-seventh for regular work, thus showing that the mule is a very efficient machine so far as effort is concerned, but very deficient as to speed. In conclusion, I would say that it is my belief that in the very near future compressed-air and electric locomotives will as thoroughly displace the mule in mines as they have the horse in street-