The process of making propane. (Gale Group)

A machine designed to convert the potential energy stored in fuel to tractive effort needed for pulling unpowered wheeled vehicles (usually in a train on railway tracks) is called a "locomotive." The complexity of this definition reflects the fact that "railroads" are a composite technology made up of tracks, locomotives, and trains. There were "trains" of wheeled vehicles pulled by animals or gravity on "tracks" laid to reduce rolling resistance before there were locomotives, but there were no "railroads" until all three components were brought together. The final link was the locomotive—one of the most useful inventions ever made. Within decades of its development locomotives had multiplied overland travel speeds and freight tonnages more than tenfold—in the process revolutionizing land transportation for all time.

History

Historians usually credit the invention of the locomotive (and hence...