796 The Outline of Science 



expensive to make, lay, and maintain ; and, in spite of the greatest 

 care, these pipes would be sure to leak and a large amount of 

 power would be dissipated. Hydraulic transmission would also 

 need very large pipes, buried deep to escape frost. For carrying 

 the energy as electricity, small insulated conductors buried in the 

 ground, or carried aloft on poles suffice. The conductors may 

 change direction suddenly, twisting and bending about to suit 

 natural conditions, without the loss of efficiency which inevitably 

 would result in the case of pipes carrying fluids. Rivers, wide 

 chasms, and other natural obstructions present difficulties not 

 comparable with those encountered by a pipe line, as the con- 

 ductors negotiate them in huge spans. 



Cheap and efficient transmission, then, makes it possible to 

 generate current in bulk at centres where conditions are favour- 

 able for generation and to deliver it over large areas at a lower 

 price than it would cost if generated in small quantities on the 

 spot. The energy converted may be either that of fuel capable of 

 transport such as coal or oil or, again, that of waste gases or 

 falling water, which can be converted profitably only where avail- 

 able. As for coal, under certain conditions it may be more eco- 

 nomical to move it to where energy is wanted, than to transport 

 current; but it cannot be denied that judiciously distributed cen- 

 tral power stations produce a given amount of power much more 

 cheaply than a multitude of independent plants. For railway 

 working, 2 Ib. of coal consumed in an electric power station will do 

 the work of 5-7 Ib. burned in a locomotive. On the other hand, the 

 energy in the waste gases from a blast furnace or in natural heat 

 must be converted on the spot or not at all. Hence many smelting 

 plants become centres from which electric power is distributed in 

 all directions as much as 4,000 h.p. being obtainable from one 

 furnace and places where terrestrial heat is available in sufficient 

 quantities acquire a new importance. Thus, at Lardarello in a 

 volcanic district near Volterra, Italy, subterranean steam is 

 brought to the surface in pipes and made to generate 10,000 elec- 



