\VI1.L1AM ^7/-..l//..\.s, l-.R.S. 2OI 



will IK- Ion ml that the magneto-electric machine recommends 

 itsi'lf, not only by its cleanliness and by the ease with which it can 

 be turned on and off at any moment, but that it is the chc;t|"T 

 machine as far as regards the consumption of coal. In work- 

 ing a small gas or steam engine, the consumption of fuel cannot 

 IK' taken at less than 8 pounds per horse-power per hour, whereas 

 in working a 100 horse-power steam engine on economical 

 principles, 2, or say 2'5, pounds per hour of coal suffice to produce 

 1 horse-power. Suppose that 45 per cent, of the power available 

 at the central station is reproduced at the distant one, the amount 

 of coal per hour consumed at the distant station would be 



2*5 x = _^-is 5'6 Ibs., or 30 per cent, less than if a gas or steam 

 45 45 



engine were directly employed. 



The principal objection that has been raised by electricians to 

 the conveyance of power to distances of miles, as here proposed, is 

 on account of the apparently rapid increase in the size of the con- 

 ductor required with increase of distance. In order that the 

 magneto-electrical machine may work under the most favourable 

 conditions, it should have an internal resistance depending in a 

 great measure upon the nature of the work to be performed, but 

 not exceeding for quantitative effects one ohm or unit of resistance. 

 If the resistance is greater, a notable proportion of the power ex- 

 pended will be converted into heat in the conductors, causing both 

 loss of effect and great inconvenience. By another law, the 

 electrical resistance of the circuit exterior to the machine should 

 be somewhat, but not much, larger than the internal resistance, 

 say 1-J- unit ; the external resistance is composed of two elements, 

 namely, the conductor and the resistance of the electric lamp, or 

 electro-magnetic engine, which latter may be taken as amount- 

 ing also to one unit, leaving only half a unit available for the con- 

 ductor. These conditions determine really the size of the con- 

 ductor for any distance to which the current has to be conveyed. 



Suppose the distance to be half a mile, a copper wire of 0*28 

 inch diameter will produce the half unit resistance to be desired, 

 which is already a wire of considerable dimensions for the purpose 

 of working a single lamp. If the distance be doubled, wire of the 

 same thickness would give twice the electrical resistance, and in 

 order to reduce it again to half a unit, its sectional area must be 



