Thousands of writers, of poets, of scholars, have laboured to increase knowledge, to dissipate error, and to create that atmosphere of scientific thought, without which the marvels of our century could never appeared. And these thousands of philosophers, of poets, of scholars, of inventors, have themselves been supported by the labour of past centuries. They have been upheld and nourished through life, both physically and mentally, by legions of workers and craftsmen of all sorts. They have drawn their motive force from the environment.