Steam Power

January 28, 2011

James Watt is connected in the public imagination to the steam engine, but Watt's story is much like that of Thomas Edison. Although many think that Edison invented the electric light bulb, what Edison did was to perfect it and make it a practical item. He did this through experimentation. The same can be said for Watt. The first practical steam engine was most likely invented by Hero of Alexandria; but it was Watt who perfected steam power through much experimentation.

Watt was well known in scientific circles, since he was a member of the Lunar Society and in the company of Erasmus Darwin, James Keir, Joseph Priestley and Josiah Wedgwood. Watt was introduced to steam power by John Robison, a physicist, mathematician and professor at the University of Edinburgh. The preeminent steam engine of Watt's day, the Newcomen steam engine, was used extensively to pump water out of mines, but it was very inefficient.

There were two major problems with the Newcomen steam engine. The first, was that the piston that did the work was ill-fitted in its cylinder, so much of the available work was lost through pressure leakage. Watt solved that problem by using the cannon boring technique developed by John Wilkinson. Watt and Wilkinson eventually partnered on this enterprise.

The second problem was that the conventional design condensed the steam inside the work cylinder by a spray of cold water. Watt found that 80% of the steam's heat was used just to reheat the cylinder. Watt built a steam engine in which the steam was condensed separately, thereby helping to propel England into the Industrial Revolution. As I mentioned in a previous article (Flying Cars and Four Day Work Weeks, December 14, 2010), steam engine efficiency increased by a factor of thirty six from 1760 to 1910, and the use of steam power in the UK increased by a factor of 2,000 in the same period.

The idea of the steam engine goes back quite a ways from Watt. The Greek mathematician and engineer, Hero (more properly, Heron) of Alexandria, demonstrated a steam engine in the first century AD. A description of this device, called an Aeolipile, is published in his book, Pneumatica. A schematic diagram is shown in the figure.

Heron's Aeolipile (Hermann Diels, "Antike Technik," Verlag B.G. Teubner (Leipzig and Berlin, 1914), p. 52)

A translation of Heron's Pneumatica can be found on the University of Rochester Steam Engine Library Web Site.[1,2] A recent article on the arXiv preprint server led me to it.[3-4] Heron's Pneumatica contains not only the Aeolipile but 77 other devices that utilize a variety of physical and mechanical principles. Heron writes that some of these are his own, but he doesn't distinguish which. There's the possibility that the Aeolipile is not strictly his invention, although the specific implementation in the Pneumatica might be. The Roman, Vitruvius, wrote in an earlier manuscript that Ctesibius (285-222 BC) invented the aeolipile.[3] Heron, however, gives an "engineering drawing" and directions for fabrication of such a device.[2]

Many of Heron's devices contain a regulator or feedback control mechanism;[3] for example,

• A Vessel which remains full, although water be drawn from it.
• A self-trimming lamp.
• A goblet into which as much wine flows as is taken out.

One of Heron's steam devices made use of not just the force of a steam jet, but also the Bernoulli Effect. This is demonstrated in a device that levitates a sphere in a vertical jet of steam.[3] The siphon effect is used in a device that opens temple doors in response to fire.[3] There is also a device that uses a windmill to activate a piston to pump air into a pipe organ.

As I mentioned, Heron is known as a mathematician as well as an early example of an engineer. In math, he's best known for Heron's formula for calculating the area of a triangle from the lengths of its sides. When I first saw it, in high school, it was the most wonderful mathematics I had seen to date. The formula is simply,

where a, b and c are the lengths of the sides, and s is (a + b + c)/2, which is called the semiperimeter.

For those of you not acquainted with the literary genre, I refer you to Steampunk.

References:

1. Steam Engine Library, University of Rochester.
2. Bennet Woodcroft, Translator, "The Pneumatics of Hero of Alexandria," Taylot, Walton and Maberly (London, 1851).
3. Amelia Carolina Sparavigna, "Water, air and fire at work in Hero's machines," arXiv Preprint, January 18, 2011.
4. Kentucky FC, "The Amazing Steam Engines Of The First Century," arXiv Blog, January 10, 2011. It's interesting that "Kentucky FC" and I are attracted to the same arXiv articles. In my case, they're the 1% of them that I understand (LOL).
5. The British Museum has four manuscripts of Heron's Pneumatica. Unfortunately, none of these are online. Robert Henry Thurston, "A history of the growth of the steam-engine," Kegan Paul, Trench, Trübner & Co. (London, 1895), 479 pages (via Google Books).
   • Heron. of Alexandria. Pneumatica and De Automatis early 16th cent., in Greek, Burney 108 ff. 27-100
   • Heron. of Alexandria. Pneumatica and De automatis, with diagrams circa 1566-1572, in Greek, Harley. 5589
   • Heron. of Alexandria. Pneumatica and De automatis, with diagrams, copied by I. Mauromates mid 16th cent, in Greek, Harley. 5605
   • Heron. of Alexandria. Pneumatica, with pen diagrams, mid 16th cent., in Greek, Burney 81 ff. 2-41v
   
6. Heron's Engine (Aeolipile) on Wikipedia.