The biggest thing an average person might introduce is something like germ theory, which could be pretty massive - but in order to get people to take your advice of washing hands and boiling water seriously, you would have to rise through the ranks of the medical establishment as it exists, which depending on time and place probably means climbing the ladder of whatever is the dominant religious institution. Only after decades of accruing social capital would you have any hope of being seen as anything but one of about a million cranks with your wild and untestable theory of "tiny animals that can't be seen".

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.

Every machine has had the same history — a long record of sleepless nights and of poverty, of disillusions and of joys, of partial improvements discovered by several generations of nameless workers, who have added to the original invention these little nothings, without which the most fertile idea would remain fruitless. More than that: every new invention is a synthesis, the resultant of innumerable inventions which have preceded it in the vast field of mechanics and industry.

Science and industry, knowledge and application, discovery and practical realization leading to new discoveries, cunning of brain and of hand, toil of mind and muscle — all work together. Each discovery, each advance, each increase in the sum of human riches, owes its being to the physical and mental travail of the past and the present.

• conquest of bread