The genius of a Séguin, a Mayer, a Grove, has certainly done more to launch industry in new directions than all the capitalists in the world. But men of genius are themselves the children of industry as well as of science. Not until thousands of steam-engines had been working for years before all eyes, constantly transforming heat into dynamic force, and this force into sound, light, and electricity, could the insight of genius proclaim the mechanical origin and the unity of the physical forces. And if we, children of the nineteenth century, have at last grasped this idea, if we know now how to apply it, it is again because daily experience has prepared the way. The thinkers of the eighteenth century saw and declared it, but the idea remained undeveloped, because the eighteenth century had not grown up like ours, side by side with the steam-engine. Imagine the decades that might have passed while we remained in ignorance of this law, which has revolutionized modern industry, had Watt not found at Soho skilled workmen to embody his ideas in metal, bringing all the parts of his engine to perfection, so that steam, pent in a complete mechanism, and rendered more docile than a horse, more manageable than water, became at last the very soul of modern industry.