The fire of Prometheus is as a rush-light compared to the volcano of steam which, like all great world forces, is a mixture of Pandora and her box; for it has given us beauty and wealth, and also ugliness and starvation. It revived the world, bled white during the Napoleonic wars, and, in place of conquering the world as the great Corsican attempted, it recreated it. When men began to move by steam power, Titans strode this earth. In peace time we see science advancing as it had never advanced before, industry growing beyond belief or imagination. Cities spring up in the night, such as Chicago, for whilst, in 1830, its population numbered a hundred souls, to-day it holds nearly three millions. Nations grew and doubled, trebled and quadrupled their populations, and the wealth of Crœsus is to-day but the bank balance of Henry Ford. Yet out of all this prosperity, created by steam power, arose the Great War of 1914–1918, which, in its four years of frenzy, was to show a surfeited civilisation the destructive power of steam. What do we see during this last period of roaring turmoil? A curious picture. The railway and the steamship, which, during days of peace, increased movement out of all belief, during war end by impeding it. Like great funnels, we see the railways, pouring forth cataracts of men, veritable human inundations, and then we see that, though it is easy to move masses by rail, once the rail is left behind, it is next to impossible to supply these masses by road, or to move them in face of gun and machine gun. The war becomes a war of trenches, not a moving war, but a stationary affair—men look at each other and sometimes shoot. As peace begets war, power and movement are the foundation of the second, just as they are of the first. On the battlefield or in the workshop, power is useless without movement. It is no good setting up a boot factory, unless you can get the boots on to the feet of the people, and in war it is no good piling up bayonets, unless you can get them into the intestines of your enemy. Thus, it happened that, before the war was three months old, though each side possessed much power, power in itself was useless, for it could not be moved. The remaining four years of the war were spent in solving the equation of power and movement. This problem was partially solved by the tank, which possessed both power and movement. And from the armies which used these machines, and there were never very many of them, little streamlets of men trickled forward out of these great stagnant human pools, and the war was won. THE RIDDLE OF THE GORDIAN KNOT