Tuesday, July 20, 2010

Ancient Technologies or Modern Fantasies?

Posted by Darin Hayton on 07/20 at 10:55 PM

Jo Marchant recent wrote a short “story” for New Scientist on the most recent interpretation of Archimedes’ burning mirrors legend: “Reconstructed: Archimedes’s flaming steam cannon.” She summarizes a recent paper by Cesare Rossi, a mechanical engineer at the University of Naples Federico II, in which he claims that Archimedes constructed a steam cannon and used it to ignite the Roman ships as the sailed into the harbor at Syracuse. In the story Marchant cites two historians—Serafina Cuomo and Tracey Rihll—both of whom politely reject Rossi’s claim.

Jo Marchant’s article on a hypothetical Archimedean steam cannon

Marchant also posted a slightly longer version of the story on her blog, “Archimedes’ flaming steam cannon,” in order to discuss “what other scholars think of the idea … in a bit more detail….” In this version she offers greater detail from Rossi before once again citing the same two experts in ancient history, science, and technology. The “bit more detail” that Marchant adds further undermines Rossi’s claim.

Marchant’s two versions of this story present yet another example of a scholar trained in the sciences dabbling in history of science and doing a bad job of it. Her two stories also raise a question: why did she bother to write them, since her two experts both reject Rossi’s claim?

Rossi’s article appears in the conference proceedings, The Genius of Archimedes, published by Springer for the bargain-basement price of $229. You can also buy just Rossi’s chapter for a mere $25.1

The Genius of Archimedes, proceedings from a recent conference on Archimedes(See the Springer website for the original image)

Fortunately, his entire article is available through google books: “Archimedes’ Cannons Against the Roman Fleet?” His logic reduces to:

  • The legend of Archimedes’ burning mirrors is well known
  • But it is unlikely that he could have ignited a moving ship using such mirrors
  • No ancient source attests to the burning mirrors
  • Leonard da Vinci sketches a steam cannon that he attributes to Archimedes
  • Parabolic mirrors can heat water to 600°C
  • Therefore Archimedes built a steam cannon

Rossi’s illustration and dismissal of burning mirrors (Source: Rossi, “Archimedes’ Cannons Against the Roman Fleet?” page 114)

Or, to use more of Rossi’s own words:
Although “everybody knows” the legend of Archimedes’s burning mirrors, so it must be true, we should not accept that he constructed parabolic mirrors to focus the sun’s rays on a ship: “it is quite impossible to concentrate in this point enough energy to sustain a fire; in addition, the fire could be easily put out by few bucket [sic] of water.”2 Moreover, “no mention about burning mirrors was made by the historians of the Greek-Roman era but this legend appears only during the middle age [sic].”3 Leonardo da Vinci provides a key to solving this puzzle: “At the end of the XV century, Leonard Da Vinci drew a steam cannon that he ascribed to Archimedes….” Leonardo’s account seems similar to one offered by Petrarch. Since we know that “nowadays, parabolic mirrors are used to obtain energy from the sun; in some application [sic] a fluid mix of salts is heated (in a pipe located in the locus of the foci of a parabolic linear mirror) up to 600°C, … it seems plausible to suppose that Archimedes used burning mirrors to heat the breech of steam cannons.”4 Q.E.D.

Rossi’s argument here is at best problematic: on the one hand, the absence of an ancient account of Archimedes’ burning mirrors is evidence that they didn’t exist. On the other hand, the same absence regarding a steam cannon is ignored while the medieval legend is taken as evidence that Archimedes built such a device. Further, Rossi’s paper relies on what engineers and scientists do today with mirrors—he repeated invokes present practices as evidence for the past—rather than what Archimedes or other ancient philosophers might have done. When he does invoke historical examples, they are all nearly a millennium after Archimedes: Cannonballs

like the one described are shown in figure 6. The one on the top left is from the fortress of Chania (X-XII Century) … the picture at the top right is reported a representation of a gun (a fire lance) and a grenade (upper right), from the cave murals at Dunhuang, c. 950 A.D. thos in the lower part of the image are ceramic bombs found on the 1281 shipwreck of the fleet who attempted to invade Japan.5

Rossi also selectively uses his sources, especially Leonardo. Leonardo claims that the water in the steam cannon was heated by a coal fire. Rossi ignores this and claims instead that the water was heated by a mirror. He also tries to explain away Leonardo’s description of the size of the cannonball, ca. 30 kg, and opts instead for a cannonball of ca. 6 kg (Rihll points out this discrepancy).

Marchant’s experts, Cuomo and Rihll, point out other obvious flaws in Rossi’s paper:

  • How did Leonardo learn of Archimedes’ invention?
  • Rossi’s rejection of details from Leonardo’s account (a solid iron ball weighing ca. 30 kg becomes a hollow clay ball weighing ca. 6 kg).
  • There is no ancient source for Archimedes’ steam cannon.
  • A better explanation of why Leonardo attributed the steam cannon to Archimedes is Archimedes’ mythic status in the Renaissance.

If Marchant’s own experts rejected Rossi’s claim, why did she bother to write the stories? Perhaps she was merely aping the story at Live Science, which was later picked up by and innumerable other sites. To give Marchant credit, at least she asked experts. The Live Science story takes Rossi at face value. Nevertheless, Marchant’s stories further disseminate sloppy history of science. Perhaps more problematically, by publishing her stories in spite of Cuomo’s and Rihll’s reservations, Marchant is actively denying expertise in the history of science.

1In an effort to keep the book affordable, Springer chose not to copyedit the book.
2Rossi, “Archimedes’ Cannons Against the Roman Fleet?” page 114.
3Ibid., 116.
5Ibid., 119.

Tags: archimedes, historiography, leonardo da vinci


Comment posted by Thony C. on 07/21 at 02:10 AM

A wonderful take down!

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