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240 connected to the third wire, whilst the terminals are attached to the two outside wires. Such a transformer is technically termed an "auto-transformer," and where the ratio of the windings is as 1 to 1, it simply serves to halve the total voltage and allow whatever out of balance current may flow in the middle wire to find its way back to the outer wires. By the means here described it is possible to give a satisfactory service of electricity over a district extending for about a mile all round the central station. The term "central station" is derived from the fact that in the early days of the public supply of electricity the works where the current was generated were placed as near the centre of the district of supply as was found possible. Now-a-days it is not a correct term. The tendency is to put the works eccentrically to the supply area; and this for obvious reasons. In the central part of the town, where there is the greatest demand for current, land is too valuable to be occupied by a works, there is the difficulty of bringing coal to the works, taking the ashes away, and there is the further difficulty of obtaining an abundant water supply for condensing purposes. It is true that if the water supply is restricted cooling