Five hundred years ago, the precision instruments of clocks, sextants, compasses, microscopes, and telescopes freed us from the limitations of our unaided sensory organs. And scarcely more than two hundred years ago, the technology of reciprocating engines liberated us from our ancient dependence on the physical power of the human body and our beasts of burden. As a result, we have conquered the world with the powers of science and the machinery of industry, and we have created immense nations in which millions of people live and work together as members of a single human society.
