As a significant example of unintended consequences, the Global Positioning System has joined the Internet as a by-product of planning for war. Both were developed by the U.S. Department of Defense and both have become wildly successful in the private sector. However, unlike the Internet, where it's often hard to find what you want, GPS makes it easy to find what you want, whether it's you, someone else, or something else.

In today's mobile society, the search for where you are, may be replacing the search for who you are. And fortunately, with GPS, finding your location is much easier and less expensive than finding your inner self. With GPS measurements, you get both horizontal and vertical position data, and the ability to calculate both direction, distance, and speed when in motion.

Following the example of other electronic devices, GPS receivers have become smaller, cheaper, and loaded with more features. And as the microchips used in them drop in size and price, they'll be put to even wider use. For instance, the Federal Communications Commission mandated cell phones must be traceable in an emergency, and one of the simplest ways to do this is with a GPS chip.

GPS also makes tracking any motion simple, from measuring the movement of tectonic plates to following the migration of endangered species. Cities can monitor the location of their emergency vehicles, or businesses their fleets, to provide the most efficient service.

Despite its sophistication, measurements made by GPS are subject to errors caused by a number of natural and mechanical sources. But even this problem has been turned into a benefit by those studying the weather. As GPS satellite signals pass through the atmosphere their speed is slowed by charged particles and water vapor. Scientists can chart the signals' speed variations to determine changes in the atmosphere.