Many people doubted that such a thing was possible, but a young inventor named Guglielmo Marconi proceeded to make good on the promise, using cumbersome sparking devices on observation boats to transmit Morse code messages to land stations a few miles away.

A hundred years later that trickle of dots and dashes had evolved into mighty rivers of information. When another America's Cup competition was held in New Zealand in early 2000, for instance, every detail of the action—the swift maneuvers, straining sails, sunlight winking in spray—was captured by television cameras and then relayed up to a satellite and back down again for distribution to audiences around the world. The imagery rode on the same invisible energy that Marconi had harnessed: radio waves.

Any radio or television signal of today, of course, amounts to only a minuscule fraction of the electromagnetic flow now binding the planet together. Day and night, tens of thousands of radio stations broadcast voice and music to homes, cars, and portable receivers, some that weigh mere ounces. Television pours huge volumes of entertainment, news, sports events, children's programming, and other fare into most households in the developed world. (The household penetration of TV in the United States is 98 percent and average daily viewing time totals 7 hours.) Unrivaled in reach and immediacy, these electronic media bear the main burden of keeping the public informed in times of crisis and provide everyday coverage of the local, regional, and national scenes. But mass communication is only part of the story. Police and fire departments, taxi and delivery companies, jetliner pilots and soldiers all communicate on assigned frequencies. Pagers, cell phones, and wireless links for computers fill additional slices of the spectrum, a now precious realm administered by national and international agencies. As a force for smooth functioning and cohesion of society, radio energy has no equal.