1082 THE COLLIERY GUARDIAN November 26, 1915. multiple or in series. The best practice is to burn two lamps, carefully selected for current, in series. Such lamps can readily be obtained, and are known as street railway lamps. For voltages above 280, the proper lamps should be selected for series burning. The table lists lamps for specific voltages. A recording chart, used as described previously, showed a maximum voltage variation of 20 per cent. From fig. 5 it will be seen that with a 10 per cent, reduction in voltage, the candle-power of the carbon lamps is 20 per cent, lower than that of the tungsten lamps. Fig. 5 shows that the characteristics of the tungsten lamp are such that voltage variation does not affect candle-power as much as it does that of carbon lamps. With regard to the comparative cost of more efficient illumination, let us take, for example, an installation such as illustrated in fig. 1, where 26 40-watt tungsten lamps and reflectors and 31 25-wa/tt tungsten lamps and reflectors are to replace the same number of 32 and 16 candle-power carbon lamps, respectively. During a period of 300 days, at 10 hours a day, the tungsten lamps would consume about 5,440 kw.-hours, while the carbon lamps would consume about 14,940 kw.-hours. With the cost of current at 0-5c. per kilowatt-hour, the saving in cost of power with the use of tungsten lamps would be about 50 dols. a year. From this must be subtracted about 17 dels, for the difference between the cost of the carbon lamps and the tungsten lamps. This will leave about 23 dols. net saving. With the reflectors costing 60 dols., the installation would be paid for in three years. These figures tend to show that if price alone were considered, it would be more profitable to use the higher efficiency lamps. This is even more marked when the illumination on the working plane is considered, because with the use of reflectors the illumination is more than double that obtained with carbon lamps. There are many other places where special applica- tions of lighting would tend to increase efficiency and convenience; for instance, trip-lights—now, as a rule, siimply oil torches on the end of the train—could be easily replaced by small storage-battery outfits showing a red light. Locomotive headlights can be equipped with low voltage concentrated filament tungsten lamps in parabolic reflectors, with a decrease in trouble, increased light, and decreased breakage over the present carbon or regular tungsten filament. Two 30 volt, 100 watt tungsten filament locomotive headlight lamps can be burned in series with a resistance. The loss in current through the resistance is a small factor as compared with the gain in steadiness and brilliancy of illumination from the parabolic headlights. The construction of this lamp is such that maximum strength of filament is obtained, which is an essential feature where the service is as severe as on a locomotive. Another possible consideration is the placing of distinc- tive lights where telephones are located, or where first- aid equipment may be obtained. This could be accom- plished by the use of red lights on the power circuit installed in connection with a small primary battery system, which would operate a miniature lamp in place of the large lamp should the power circuit for any reason fail. From the figures given above, it will be seen that the application of the latest scientific knowledge to the lighting of mines is less expensive than generally thought, and should be considered as a means of increas- ing safety, bettering working conditions, increasing production, and at the same time decreasing the cost of operation. Partnership Dissolved.—The London Gazette announces the dissolution of the following partnership :—J. C. Gisburn and J. Henderson, engineers, at Great Wilson-street, Leeds, under the style of the Adelphi Engineering Company. Pit Prop Contract Dispute.—Mr. Justice Bailhache, in the King’s Bench Division, on Friday last, gave judgment in an -action respecting a valuable cargo of pit props which arrived at West Hartlepool four days after the war broke out. The action was that of Oluf Christian Wulfsberg and Company, Putney, S.W., against Dymock and Company, of 147, Corporation-street, Birmingham, and was for extra payment, in the circumstances, said to be due to the plaintiff. The sum was also the subject of a counterclaim by the defendants, who sought to recover. His lordship, giving judgment, said the cargo arrived on the steamer “0. A. Knudsen.” Plaintiffs had had a contract to supply defendants up to 3,400 fms. maximum option, and from two other shipments had supplied 1,500 fms. Messrs. Dymock, on the ‘‘0. A. Knudsen ” shipment consented to pay .£200 above the agreed price, which was stated in letters to be towards war risks. No war risk policy, how- ever, was taken out. When Messrs. Dymock discovered this they said they had no need to pay, urging (1) that there had been a mistake in fact; and (2) that they could not be expected to pay in respect of a consideration which had failed. With the outbreak of war there was anxiety about the ship and anxiety about the cargo, because the price of pit props had greatly risen. With the ship safe in port, Mr. Dymock was thankful to get more than his maximum quantity, and glad no question was to be raised whether the war would put an end to the contract; he stood to make a handsome profit; and at that time was very easy-going as to the .£200, and did not much care whether there was a policy or not. He got the cargo delivered to him on agreeing to Wulfsberg’s terms. On the score of non- fulfilment of consideration there were several factors. There had been only a partial failure and not a complete failure of consideration; and that legal ground failed the defendants. The counterclaim failed, and there must be judgment for the plaintiffs for £200 and costs. UNEXPECTED EMISSION OF GAS.* By F. 0. Cornet. The accompanying sketch shows a cross section of the mine workings skirting a large worked out territory. The weight of the overlying strata has forced down a narrow pillar of coal into the soft slate pavement. This pillar for nearly half a-mile separates the worked out area from an important air course, which serves to ventilate distant workings where a number of men are employed. The air course is also a drain for the abundant waters that find their way from the surface into the mine through the worked out territory. Although the pillar to the left of the air course has sunk nearly 2 ft. into a soft bottom, the pillar on the opposite side has not yet been appreciably driven down- ward. There seems no doubt, however, that this pillar is slowly sinking, and would have sunk deeper had it not been that the water from the worked out area was intercepted by the air course and so diverted to the outside. No doubt some of the water finds its way towards the place designated as ” haulway,” seeping there through the soft slate pavement, softening the latter and thus making it give way slowly but surely under the weight of the 1,400 ft. of hill bearing upon it. As shown by the sketch, when the pillar on the left sank into the soft bottom, rendered still softer by water, it compressed this bottom so that some of it was squeezed outward. As there was no empty space to the left, it is not likely that much, if any, of -the slate forced out went in that direction. But there is ample evidence that much of it was driven into the air course, causing the pavement to heave until only one-half of the original head room was left. AJR_C0UR5E_:QroS/a-fe Wafer L*yg/ CROSS-SECTION OF MINE WORKINGS Under the soft slate that constitutes the pavement of this seam, another seam of coal is always found, the thickness of which varies from a few inches to several feet. The thickness of the intervening slate runs from 2 to 80 ft. At the particular point shown by the sketch this slate was found to be 5 ft. thick, and the lower seam of coal to measure 18 in. The lower seam rests, without adhering, on the highly polished surface of the hardest kind of sandstone. Its unusual smoothness indicates that in remote geologic times there' must have been much friction caused by the coal sliding on the sand rock, or the sand rock moving under the coal. The lower seam does not adhere much to the overlying soft slate, but the contact surface is uneven and rough enough to make it likely that when the 5 ft. of soft slate was squeezed out toward the air course there w<»$ a tendency on the part of the lower seam to go with it at least part of the way., especially as such a displace- ment was facilitated by the smooth and polished condition of the surface of the sand rock lying under- neath. It is not hard to imagine that in the lateral displacement of both the soft slate and the lower seam such conditions might be caused as shown by the sketch, in which the soft slate not only has heaved into the air course above, but has also separated itself from the coal underneath after displacing it and causing fissures to appear in it running in all directions. The lower seam might also have been raised partially above the sandstone. Cavities would thus be formed as shown, partly filled with debris of slate and coal, but open enough to afford easy inter- communication between all the cracks and fissures mentioned. The heaving of the floor of the air course could not well occur without some cracks appearing in the slate of which the floor is constituted. One or more of these cracks reaching through the 5 ft. of slate would suffice to maintain a free outlet into the air course for any gas liberated by the lower seam. The mine where this condition obtains is in one of the seams of the New River series. Operations had been prosecuted in it for several years, and had reached far into the hills. Notwithstanding the most watchful vigilance, no gas had ever been detected in the work- ings. More or less vaguely the authorities knew of this lower seam, but they never gave it more than a passing thought, being far from expecting trouble from its presence. One morning, however, a year ago, a man had his hair and eyebrows singed through setting fire to a small body of gas near the roof, in a place where nothing but fresh air coming direct from the fan was supposed to travel. During the next 10 days four more ignitions took place, under like conditions, and on a split of air between the fan and the first working places. No air reaching the spots where the accidents occurred could possibly have swept any coal, except such as had been exposed to a ventilating current for at least two or three years. No gas had ever been found at the faces. But any gas that might have been found there could not by any means have been made to travel toward the fan, against the air. After the first ignition, the officials proposed making an inspection of the airways by travelling against the current from the spots where the accidents had happened, but they soon ran into some water 2 ft. deep, and the inspection stopped there. * Coal Age. After four more explosions had occurred, a pair of rubber boots was telephoned for, and a man carrying a safety lamp was sent through the water. He did not see anything, but soon heard gas bubbling through the water, and hastened to report his discovery to the fore- man, who immediately understood how the mysterious accidents had occurred. A thorough investigation was made, and the sketch incorporated in this paper was prepared. The ventilation was reversed so that the fan drew the air to the mine mouth instead of driving it toward the working faces. Though a year has since elapsed, the gas from the lower seam is still passing through the cracks in the floor and bubbling through the water in large quantity, which tends to show that when the soft slate was squeezed out from under the narrow aircourse pillar, it must have disturbed and creviced a large area of the lower seam; otherwise such a large amount of gas would not have been liberated. THE FLOW OF ENERGY THROUGH TRANSMISSION LINES.* By Robert A. Philip, M.A.LE.E. (Continued from page 980.) Power consists of the product of -two components, velocity and pressure. Either may be increased at the expense of the other, and the power remains the same. Mechanically, increase of pressure with decrease of velocity may be accomplished by gearing. The trans- mission of power through gearing makes no change in the direction of its flow, nor in the width of the stream, except for the diversion of a small amount correspond- ing to the losses in the gearing. Transformers are used for increasing electrical pressures with corresponding decrease in current. A transformer is, therefore, a kind of electrical gearing, and power will pass through it with no change except a slight diminution to cover transformer losses. Accelerating power can be geared up or down mechani- cally just as well as energy flow. Similarly magnetising power can be transformed as readily as energy flow. A transformer is therefore no barrier to the free and independent flow of the two kinds of power. The electric transformers are a type of gearing corresponding mechanically to a direct-acting pump; the change of pressure being produced by alternating or reciprocating motion. The transformer, therefore, must itself receive a small amount of magnetising power in order to work at all, but this is an approximately fixed amount, and-does not otherwise affect the free flow of magnetising power through it. Transformer Alternating Exciter Generator Alternating Exciter Generator Induction Motor • full load (IrxluchveK8oXPF lagging) __ 60 H-V-A. I HALF LOAD t-ii"PS fA'on induc';re)(iOO?.P.F) J'S Transformer Synchronous Motor Exciter Transformer Induction Generator Fig. 6.—Flow of Energy and Magnetisation THROUGH A TRANSFORMER. The magnetising power taken by a transformer is similar in characteristics to that of an induction motor, the principal difference being that the magnetic design of a transformer is much more perfect that that of an induction motor, so that the proportion of magnetising power taken is much smaller. Fig. 6 shows the flow of power through a -transformer. The transformer diverts from the energy stream a small branch which is con- sumed as transformer loss, and from the magnetising stream another small branch which magnetises the core. Even at no load the transformer must receive these two small streams if it is active. Ordinarily both streams come from the same direction, that is from the generator, but this is not essential, for when an induction generator drives a synchronous motor through the transformer •the energy loss stream comes from the generaotr, the magnetisation stream from the motor. In a broad way, generators and motors as well as transformers may be considered as a kind of gearing. A generator, like a transformer or a gear, transforms the product of one motion and one pressure into an approxi- * From a paper read at the joint meeting of the Chicago Section of American Institute of Electrical Engineers and the Western Society of Engineers.