American Scientist

Energy has seldom been found where we need it when we want it. Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame. With more settled people, animals were harnessed to capstans or caged in treadmills to turn grist into meal. Locating a mill beside a river or stream provided an alternative, but rivers flood and streams dry up, interrupting the steady flow of energy. In estuaries, the energy of water could be trapped behind dams at high tide and released at low to drive waterwheels that turned gears that drove millstones and saws. It was only with the Industrial Revolution that there came a more constant and portable source of power—as long as the supply of input energy remained readily available in the form of wood and coal to maintain a fire to heat water and produce steam. The concept of mounting steam engines on wheels gave us railroads, but they had to stop now and then to take on more fuel and water. The development of automotive vehicles freed the engines from the rails, but there remained the problem of refueling them, which meant that fuel had to be predictably available beside the road.