Annie Staffan, age 9, of Boise, Idaho, for her question:
WHO BUILT THE FIRST STEAM ENGINE?
A scientist named Hero who lived in Alexandria, Egypt, made the first steam engine in 120 B.C. His engine was made up of a small, hollow globe mounted on a pipe running to a steam kettle. Two L shaped pipes were fastened to opposite sides of the globe.
When steam rushed out of the two L shaped pipes in Hero's engine, it caused the globe to whirl. This engine, however, performed no useful work. Many hundreds of years had to pass before the first successful and useful steam engines were developed during the 1600s.
The first practical steam engines worked on the ability of steam to condense back into a liquid rather than on its ability to expand. When steam condenses, the liquid takes less space than the steam.
An Englishman named Thomas Savery in 1698 patented the first practical steam engine. It was a pump used to drain water from mines. The pump had no moving parts other than valves operated by hand. These were turned to let steam enter a sealed vessel.
In Savery's engine, cold water was poured on the vessel to chill it and condense the steam. Then a valve was opened so the vacuum in the vessel could suck water up a pipe.
An English blacksmith named Thomas Newcomen in 1712 invented another steam engine pump for mines. A piston which fitted into a cylinder hung from one end of a beam. When steam was let into the cylinder, it forced the piston up, lowering the other end of the beam.
James Watt took out a patent for his first steam engine in 1769. In Watt's invention, the condenser and the cylinder were separate. The cylinder always remained hot. This saved three fourths of the fuel costs, because none of the steam was lost through condensation by entering a cold cylinder.
Many believe mistakenly that Watt, a Scottish engineer, invented the steam engine. He didn't. But he did improve it by reducing the cost of operating condensing engines and made it practical to use these engines for other kinds of work than pumping.
In the early 1800s, an Englishman named Richard Trevithick designed and built the first high pressure steam engine. One of his first engines operated under 30 pounds of pressure.
In 1815, an American named Oliver Evans built an engine that used 200 pounds of pressure. Today, many engines use steam under a pressure of more than 1,000 pounds per square inch.
One of the best improvements in steam engines was the development of superheated steam. In superheating, the temperature of the steam is raised above 700 degrees Fahrenheit without increasing the pressure. This keeps the incoming steam from condensing on the surface of the piston cylinder, because superheated steam does not cool so quickly as ordinary steam.
In the late 1800s, the invention of steam turbines marked another big improvement in steam engines. They provided an economical source of power to turn electric generators, and to drive the propellers of steamships.