374 THE ADDRESSES, LECTURES, ETC., Of 



not all used at one and the same time. No allowance is made in 

 this estimate for the transmission of power, which, in course of 

 time, will form a very large application of electric energy ; but 

 considering that power will be required mostly in the day time, 

 when light is not needed, a material increase in plant will not be 

 necessary for that purpose. 



In order to minimise the length and thickness of the electric 

 conductor, it would be important to establish the source of power, 

 as nearly as may be, in the centre of the parish, and the position 

 that suggests itself to my mind is that of Golden Square. If the 

 unoccupied area of this square, representing 2,500 square yards, 

 was excavated to a depth of 25 feet, and then arched over so as 

 to re-establish the present ground level, a suitable covered space 

 would be provided for the boilers, engines, and dynamo-machines, 

 without causing obstruction or public annoyance ; the only erection 

 above the surface would be the chimney, which, if made monu- 

 mental in form, might be placed in the centre of the square, and 

 be combined with shafts for ventilating the subterranean chamber, 

 care being taken of course to avoid smoke by insuring perfect 

 combustion of the fuel used. The cost of such a chamber, of 

 engine power, and of dynamo-machines, capable of converting that 

 power into electric energy, I estimate at 140,000. To this 

 expense would have to be added that of providing and laying the 

 conductors, together with the switches, current regulators, and 

 arrangements for testing the insulation of the wire. 



The cost and dimensions of the conductors would depend upon 

 their length, and the electromotive force to be allowed. The latter 

 would no doubt be limited, by the authorities, to the point at 

 which contact of the two conductors with the human frame would 

 not produce injurious effects, or say to 200 volts, except for street 

 lighting, for which purpose a higher tension is admissible. In 

 considering the proper size of conductor to be used in any given 

 installation, two principal factors have to be taken into account ; 

 first the charge for interest and depreciation on the original cost 

 of a unit length of the conductor ; and, secondly, the cost of the 

 electrical energy lost through the resistance of a unit of length. 

 Tlje sum of these two, which may be regarded as the cost of con- 

 veyance of electricity, is clearly least, as Sir William Thomson 

 pointed out some time ago, when the two components are equal. 



