towers may be used, but then there is the probability that these, by giving off steam, will prove a public nuisance. The noise and vibration inseparable from the use of powerful machinery have also to be taken into consideration, so that on the whole a central position for the electricity works becomes impossible. If we still speak of a central station, the term must not be used in a topographical sense, but rather as indicating that in those works the generation of electricity required over an extended area has been centralised.
But if we place the station outside the boundary of the town it is no longer commercially possible to supply the district with current at the moderate pressure of 440 or 500 volts. The feeders are necessarily long and their resistance is high. To get an efficient transmission system we must raise the pressure to a very much higher value, far above that which is suitable for the lamps. This leads to the establishment of so-called "sub-stations" within the supply area. These sub-stations receive high-pressure current from the central station outside of the town, and convert it to such a pressure as renders the current directly applicable. Thus the
