A steam engine is an engine that uses steam to power itself. The steam engine is one of the oldest engines, dating back some two-thousand years. The steam engine has played an important role in the Industrial Revolution, and in the modern world the steam engine accounts for more than half of the electricity in the entire world.

A steam engine consists of basically two parts: a motor, and a steam generator. A steam engine might also include condensers to collect the steam and return it as water to the system, superheaters to allow the steam to reach temperatures it wouldn’t naturally achieve, and pumps to provide a consistent flow of water. Traditionally, heat for a steam engine was provided by burning something, usually either wood or coal, in a steam box. In modern times this heat may instead be provided by tapping geothermal heat, or by creating nuclear reactions and capturing the heat from that process.

Hero of Alexandria described the earliest known steam engine in the 1st century. This type of steam engine was not used for any sort of real power generation, but rather served as a model to discover the properties of steam itself. Some of the most in-depth experiments involving steam were done by Giovanni Brance in the early-17th century and Taqi al-Din in the mid-16th century.

At the end of the 17th century, Thomas Savery created the first truly practical steam engine. He used a steam engine to power water pumps, which, in spite of some flaws, were used in a limited capacity in mining operations. In less than two decades Thomas Newcomen invented an even more useful steam engine, which saw much wider use draining mines. Not long after, James Watt improved the efficiency of Newcomen’s steam engine immensely, creating a steam engine that operated roughly 400% more for the same amount of coal.

Watt’s steam engine was an enormous step in the progress of the Industrial Revolution. Prior to his steam engine, factories needed to be built next to running rivers to power waterwheels. Watt’s invention meant that factories could be built anywhere, so the core of the industrial revolution could spread widely and quickly.

In the 19th century, the steam engine was shrunk considerably, and made even more efficient. This meant the steam engine could actually be placed on a vehicle, which led to some rather eccentric steam-powered transportation for a brief time during the Victorian era.

The most iconic steam engine is probably the steam engine on a steam locomotive. This is a relatively inefficient steam engine, as most of the waste heat is just vented into the atmosphere and little of the water is recaptured, but it was nonetheless a major use of steam power for many years. In modern times one is much more likely to find a steam engine as part of a power plant. Energy is generated, often by the burning of coal or a nuclear reaction, and that heat energy is then run through water which is turned to superheated steam. This steam then turns turbines, which generate electricity. Although many people think of steam engines as a thing of the past, in fact they are the major engine of the modern world, and there is a great deal of work put into developing new advancements and improvements in efficiency.