First, let us recall how potent a role electricity has come to play in social life through the great discoveries which began at the end of the eighteenth century. To do this we need only compare the present relationship between production and consumption in the economic sphere with what it was before the power-machine, and especially the electrically driven machine, had been invented. Consider some major public undertaking in former times - say the construction of a great mediaeval cathedral. Almost all the work was done by human beings, with some help, of course, from domesticated animals. Under these circumstances the entire source of productive power lay in the will-energies of living beings, whose bodies had to be supplied with food, clothing and housing; and to provide these, other productive powers of a similar kind were required near the same place. Accordingly, since each of the power units employed in the work was simultaneously both producer and consumer, a certain natural limit was placed on the accumulation of productive forces in any one locality.