and why by the adoption of a particular method of using the conductors a satisfactory service to all customers of an electricity works can be given, let us take by way of example the service of electricity to the house-holders along a street a mile long, the electricity works being at one end of this street. Here we have some customers quite close to the place of generation and others a mile away. If we were simply to connect the home end of these cables with the machines and supply the whole of the street from this one end only, we should get so great a variation in the voltage in different houses as to make the supply very unsatisfactory. The customers close by would get far too high a voltage and their lamps would be destroyed by "over-running," and the customers at the other end of the street would get hardly any light. The variation of delivery voltage legally permitted to public supply companies by the Board of Trade regulations is plus or minus 4 per cent., but even this seemingly moderate variation would be intolerable to the user of electric light if it occurred suddenly. The light given by an incandescent lamp varies at a much greater ratio than the voltage, about four to six times as much, so
