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What is the earliest a practical steam Engine can be built? Practical means that it's not a mere toy, but can be used by public and private organizations as a mean to improve administrative or military efficiency or to produce profit. Hero's aeolipile is a steam engine, but doesn't fulfill the condition of practicability and profitability; Newcomen's atmospheric engine is practical and profitable for pumping waters out of mines, but due to it's flaws, it's use is limited to propel pumps, so I would call it only semi-practical - I don't know if original Newcomen engines were ever used to provide factories with energies. The first really universal engine was Watt's engine, since it really could be use for mulitple and universal applications, like powering mills or steam boats. However, the real breakthrough was the high-pressure engines, since these could be used for all purposes, most notably constructing steam locomotives.

Here some of the important OTL dates:
  • 30-15 BCE: The Roman architect and engineer Vitruvius writes De Architectura, mentionning aeolipylae for the first time, but maybe he copied the works of Ctesibius, probably the first head of the Museum of Alexandria in the 3rd century.
  • 1st century CE: Hero of Alexandria's describes the aeolipile, a primitive jet engine, along with ideas like a vacuum and other means to use thermal energy and steam pressure. However, he considers his sophisticated automats as mere toys, maybe because he recognizes that his machines can't be used effectively for any economic purpose.
  • In the next centuries, again and again stories of aeolipiles and other steam engines are reported from Europe, Turkey and even China - however, these weren't really succesful and none bore fruits.
  • 1630 CE: In a letter, Italian physicist Baliani asks Galileo Galilei why water wasn't rising through a system of syphons 21 metres high. It's possible that Gasparo Berti thereupon built a water barometer between 1640 and 1643 - some sources report the same for Baliani in 1641.
  • 1638 CE: In his Discorsi, Galileo discusses the problem and determine that it's impossible to raise a column of water any higher than 11 metres - this was contradictory to to the Aristotelian concept of the horror vacui, which stated that nature abhors vacuum and thus water would fill any empty place, so that there's no limit to the height to which water can be raised. Galileo tries to explain the problem by stating that the resistenza del vacuo is to weak to achieve more.
  • 1643 CE: Galileo's disciple, Evangelista Torricelli, who took over the problem after his master's death, conducts an experiment to investigate the effect and prove that air has weight - he uses first water, but then at the recommendation of Galileo finds out that mercury is even more effective (about 13.6 times more dense than water at room temperature), so he can uses a tube of 75 cm instead of 10.5 m. The weight that the air exerts on the mercury in a bassin holds up the mercury column, and the space above the liquid was probably the first man-made vacuum, proving the ideos of Hero who believed that a vacuum was possible, but never achieved to create one.
  • 1644 CE: Torricelli announces that the pressure of the atmosphere corresponds to a column of mercury 75 cm in height or a column of water 10.5 m in height. 1 atmosphere is thus equivalent to about 76 cm of mercury.
  • 1648 CE: A barometer is carried to the top of the 1,465-m moountain Puy de Dôme by Florin Perier, brother-in-law of Blaise Pascal. The height of the mercury in it falls by 8.6 cm, which confirmes that the pressure of the atmosphere falls with increasing altitude.
  • 1649 (or 1654) CE: Otto von Guericke invents the first vacuum pump.
  • 1654 CE: Von Guericke demonstrates the force of atmospheric pressure using the experiment of the Magdeburgh hemispheres.
  • 1669 CE: Robert Boyle, in his work Continuation of New Experiments described plans for a truly portable barometer and uses the word "barometer" for the first time already in 1665/6.
  • 1679 CE: Denis Papin, having worked with Robert Boyle since 1676, invents a cooking pot, the steam digester, a high-pressure cooker. He also adds a steam release valve to prevent explosions of the machine, thus creating the first safety valve. This early safety valve consisted of nothing more than a lever and a weight.
  • 1680 CE: The Dutch Christiaan Huygens suggests to use the explosion of gunpowder in a cylinder to create a partial vacuum. The atmospheric pressure would then drive a piston into the cylinder.
  • 1690 CE: Inspired by his works on the steam digester and the idea of his patron Huygens, Denis Papin builds the first piston steam engine. He replaced the exploding gunpowder with cooling steam, with the piston being driven back into the cylinder by atmostheric pressure.
  • 1698 CE: Thomas Savery demonstrates his fire engine called The Miner's Friend for the first time.
  • 1712 CE: Thomas Newcomen installs his first atmospheric engine.
  • 1720 CE: Jacob Leupold designs a high-pressure steam engine which was never built.
  • 1765 CE: James Watt invents the seperate condenser, but can't build an improved steam engine until John Wilkonson invents a precise boring machine in 1776.
  • 1769 CE: John Smeaton start experiments with Newcomen engines and substantially improves them.
  • 1779 CE: A crank added to the Newcomen engine made rotary motion possible. In 1782, Watt creates his own rotative engine using a sun and planet gear.
  • 1781 CE: The first compound engine is patented, which is more effective than Watt's single-acting engine.
  • 1783 CE: Watt builds his first double-acting system and adds a centrifugal governor to it.
  • 1783 CE: The Pyroscaphe, the first paddle steamer, is tested in France.
  • 1799 CE: Richard Trevithik builds the first high-pressure steam engine, followed by Oliver Evans in the US in 1801.
  • 1804 CE: Trevithik builds the first locomotive, propelled by a high-pressure steam engine.
  • 1807 CE: Robert Fulton builds the Clermont, the first viable steamboat.
Well, now I wrote much more than I wanted when I started the thread. According to my source (wikipedia), the discoveries needed for the invention of the steam engine were:
  • The concenpt of vacuum
  • The concept of pressure
  • Techniques for creating a vacuum
  • Means for generating steam
  • The piston and cylinder
Now what do you think - how early could these preconditions be met by human technology? I think that the quality of steal and iron is another important issue, so if you have information of this subject, I would be glad if you would share it with me.

To sum up my question: What's the earliest the steam engine could have been invented?

GWFuckyeah
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