in course of erection or the compressor would have to be driven by steam, it was decided to employ electrical driving for the mill only. The compressor referred to, having only one cylinder, does not constitute a desirable load for an electric motor. Compressors which are to be electrically driven should have at least two cylinders, with their cranks at right angles, but three cylinders are much to be preferred. Single crank compressors are quite

unsuitable.

All the pumps in the mine are of the three-throw single-acting type, and give an approximately uniform moment of resistance. These are the most suitable force-pumps for electric driving and work satisfactorily; but for moving a large volume of water through a comparatively small lift the centrifugal pump has no equal. In the Burma Mine Installation already referred to, 12-inch centrifugal pumps are to be used, coupled directly to two-phase motors, lifting 40 feet and running at 800 revolutions per minute. The advantage of dispensing with all gearing here is apparent, and the moment of resistance is absolutely uniform. Working. It was estimated that 500 HP. would be yielded by the water, but experience soon showed that this estimate was too favourable for certain seasons of the year. It is doubtful whether the water can be relied upon to supply at the mine, continuously, more than 250 HP., but this will provide for 120 stamps, with the pumping and lighting. Oil insulation for the transformers having been abandoned at the start, the running has been a record of smooth working. The following Table gives the gross running time for the 12 months ending September, 1897, and it will be

observed that out of a possible 365 days, the pressure was off the conductors for less than 4 days. During this period 46,000 tons of ore were milled.

The mill runs day and night, and these results were obtained at a time when there was no spare plant installed; both turbines, two generators, and the whole of the gearing, ropes, belts and shafting having to run continuously. It is not unusual after the clean-up at the beginning of a month, to run to the end of the month without stopping. The time of stoppage is occupied chiefly in inspecting the water-race, overhauling belts, ropes, &c., and in executing general repairs to the machinery.

The turbine governors are not wholly relied upon to control the speed. The crushers are very trying to any governor, and the arrangement of driving one countershaft by two turbines of different size is capable of considerable improvement. On account of the slow governing it was found necessary to institute a code of bell signals, and these are worked through the telephone wire, between the power-house and the mill, relays in the telephone instruments being used to strike 6-inch gongs.

The staff at the power-house consists of eight Europeans and twelve natives, and three shifts are worked per day. Every half hour simultaneous observations are taken on each instrument in use, and these are recorded in a log-book. Remarks upon the running are also made and signed by the chief chargeman. This stimulates a healthy rivalry between the shifts.

When running a quartz mill for the production of gold, there is no time to conduct tests or to make experiments; the object of the management being to keep the mill working. Accordingly, there have been no carefully-conducted tests of efficiency, but the following results are sufficiently near the truth to indicate what may be expected from such plant.

At the time the observations were made, the 30-inch Victor turbine only was driving with 30 feet head of water. According to the makers' lists, the wheel with this fall gives 200 brake HP. :

It may be assumed that 5 per cent. of the power of the turbine was absorbed by the ropes, belts and countershafting, so that only 95 per cent., or 190 brake HP., reached the alternators.

The Author is convinced that for driving mining machinery, alternating currents of two phases possess in many respects great advantages over continuous currents, and this is quite irrespective of whether the power is transmitted at high pressure from a distance or is distributed at a comparatively low pressure from a local generator. Though the induction motor is much superior to the continuous-current motor as an electrical machine, engineers in England are only beginning, and with some diffidence, to take it up, but a few years will no doubt see a great change in this respect.

In conclusion the Author desires to acknowledge his indebtedness to the Chairman of the Sheba Gold Mining Company, to the Company's Chief Engineer, Mr. John Rance, and to the contractors, Messrs. Johnson and Phillips, for the aid they have given him in the preparation of the Paper.

The Paper is accompanied by eight tracings, from which Plate 2 and the Figures in the text have been prepared.

[DISCUSSION.

Discussion.

Mr. W. H. PREECE, C.B., President, said it was his pleasant Mr. Preece. duty to propose that a vote of thanks be awarded to the Author for the very practical Paper that he had submitted. The Institution was always gratified, in these days of severe foreign competition, to hear that an English firm had fitted a mine in a distant country with apparatus designed in England, and the members were much indebted to the Author for having given so fully and completely all the details of the measurements, of the power exerted, the efficiency, and the other conditions realized by the machinery. He called the members' particular attention to the fact that in all the Papers on electric machinery and electrical appliances brought before the Institution, the one striking element was the fact that means and instruments were applied to measure, with the greatest possible accuracy, every factor in that machine. There was nothing that tended so much to improve machinery of any kind as a system of measurement of that character.

Mr. Esson, having exhibited on the screen a series of photo- Mr. Esson. graphs of machines described in the Paper, referred to the method of driving from two turbines on one countershaft. It left much to be desired, and had only been adopted because the engineers of the Sheba Mining Company insisted on using some old plant that was on the ground. If the two turbines had been of the same size the disadvantage would not have been so great, but with turbines of two sizes, working on a common countershaft, there was a great difficulty in proportionally distributing the load between them. Accordingly a loss of about 5 per cent. was incurred in driving the countershafting. Instead of a return of 70 per cent. at the mine, 75 per cent. might have been realized if a method had been adopted whereby all the countershafting and driving-gear could have been dispensed with. In the Burma ruby mine installation there was a low fall as at Sheba, but each alternator was directly driven by ropes from a single Pelton wheel, and consequently nothing intervened between the wheel and the alternator but one set of ropes; there was no countershafting to drive. All the wheels were controlled by one governor, and that was essential. The only proper way of governing a number of Pelton wheels, driving alternators which had to work

Mr. Esson. in parallel, was to control all by one governor. In another transmission installation in the Straits Settlements, upon which Messrs. Johnson and Phillips were engaged, 300 HP. had to be conveyed to a mine 7 miles distant. There was a high fall, and the Pelton wheels were running at a speed of about 400 revolutions per minute, so it was possible to couple the alternators direct on to the Pelton-wheel shafts. That was by far the best method of working, and it had been also arranged that one governor governed the three wheels. The type of generator shown in Figs. 3, Plate 2, had been recently modified by interlacing the coils as in the motors, because it was found that then a much smaller fall of potential between light load and full load was obtained than when the coils were wound singly. The machine shown in Figs. 3, Plate 2, consisted practically of two singlephase alternators, the top half of the armature constituting one machine, and the bottom half the other; but with the interlaced coils a much better result was obtained than with the type of machine shown. Again, the field-magnet described in the Paper had been changed. It was a very good one for machines which ran on a non-inductive load, that was, on a load of lamps, but on an inductive load there was too much magnetic leakage, so it had been abandoned, and now a field-magnet of radial poles, each having a separate coil wound on it, was used. A much smaller fall of potential was thus secured than with the type of field-magnet used at Sheba. With regard to the relative outputs of two-phase and single-phase machines, if a non-inductive load was put on a two-phase machine, undoubtedly its output was higher, quite one-half more, than with the singlephase machine; but generally, the two-phase machine had to work on an inductive load, and there was not the advantage which would be obtained from working on the non-inductive load. First, for a given output, the impressed electromotive force had to be about 25 per cent. greater than the terminal electromotive force when working on an inductive load. Again, a current 25 per cent. in excess of that which would accord with the watt output of the machine had to be generated. There was thus obtained from the two-phase machine, working on an inductive motor load, just about the same output as was obtained from a single-phase machine of the same size, working on a non-inductive load. He had not, in the Paper, touched upon the application of the induction-motor to coal-mining; but in this industry it had a distinctly important bearing, as in gold-mining and gem-mining. One of the great advantages of the induction-motor was that it