From the conception of mechanical force as coming in from Nature to the service of man, a conception the Utopian proposal of a coinage based on energy units would emphasise, arise profound contrasts between the modern and the classical Utopias. Except for a meagre use of water power for milling, and the wind for sailing--so meagre in the latter case that the classical world never contrived to do without the galley slave--and a certain restricted help from oxen in ploughing, and from horses in locomotion, all the energy that sustained the old-fashioned State was derived from the muscular exertion of toiling men. They ran their world by hand. Continual bodily labour was a condition of social existence. It is only with the coming of coal burning, of abundant iron and steel, and of scientific knowledge that this condition has been changed. To-day, I suppose, if it were possible to indicate, in units of energy, the grand total of work upon which the social fabric of the United States or England rests, it would be found that a vastly preponderating moiety is derived from non-human sources, from coal and liquid fuel, and explosives and wind and water. There is every indication of a steady increase in this proportion of mechanical energy, in this emancipation of men from the necessity of physical labour. There appears no limit to the invasion of life by the machine. Now it is only in the last three hundred years that any human being seems to have anticipated this. It stimulates the imagination to remark how entirely it was overlooked as a modifying cause in human development. [Footnote: It is interesting to note how little even Bacon seems to see of this, in his New Atlantis.] Plato clearly had no ideas about machines at all as a force affecting social organisation. There was nothing in his world to suggest them to him. I suppose there arose no invention, no new mechanical appliance or method of the slightest social importance through all his length of years. He never thought of a State that did not rely for its force upon human muscle, just as he never thought of a State that was not primarily organised for warfare hand to hand. Political and moral inventions he saw enough of and to spare, and in that direction he still stimulates the imagination. But in regard to all material possibilities he deadens rather than stimulates. [Footnote: The lost Utopia of Hippodamus provided rewards for inventors, but unless Aristotle misunderstood him, and it is certainly the fate of all Utopias to be more or less misread, the inventions contemplated were political devices.] An infinitude of nonsense about the Greek mind would never have been written if the distinctive intellectual and artistic quality of Plato's time, its extraordinarily clear definition of certain material conditions as absolutely permanent, coupled with its politico-social instability, had been borne in mind. The food of the Greek imagination was the very antithesis of our own nourishment.