Sunday, June 25, 2006

Peter Dear, Galileo, Jesuits, and Material Culture

Several years ago I read a paper by Peter Dear. The overall gist of the paper--I can't really remember the title--was about the ways in which Galileo used rhetorical practice to defend his discoveries and methods against attacks from his Jesuit opponents. The details are hazy and my recollection may be completely corrupted but I do remember the point of the paper was about rhetoric.

In retrospect, Galileo's method seems a bit dodgy. I recall that Dear discussed experiments in which Galileo rolled cannon balls down planks to study the effect of gravity. The assumption is that this apparatus was an efficient analog for an earth-bound gravitational system. It was read as a perfect sphere interacting with a frictionless plane at a particular azimuth.

Forget rhetorical practice. From a technology perspective, this apparatus seems woefully inadequate. I'm reminded of an anecdote recounted in Adrian Johns's The Nature of the Book. At one point Robert Hooke apparently challenged the astronomical findings of one of his fellow Royal Society members by attacking his fellow's knowledge of how to actually construct a telescope. While I forget that fellow's name, I do remember that the challenge had something to do with which way the convex face of a lens should face in a reflecting telescope. Regardless, the member didn't know the answer and had to flee in shame.

Consider Galileo's apparatus. Lets start with the perfect plane or, as it were, the plank. It seems plausible that he had access to decent boards. Villard de Honnecourt's sketchbook from the thirteenth century depicts a water-driven saw mill complete with a multi-point linkage. Furthermore, Jacques Besson's theatrum machinarum of 1569 contains several designs for saw mills. Usher's A History of Mechanical Inventions notes that French charter references to mills began in the fourteenth century (1376, 1391, 1393, 1400, 1415) and that there are mentions of German sawmills in 1337 and 1389. Even milled boards can be rough and I'm unsure of when wood planes and scrapers became popular. Looking at the elaborate choir stalls of medieval cathedrals, however, would indicate that man certainly had the capability to produce a very smooth plank when Galileo conducted his experiments. Score one for Galileo.

A more challenging issue is the perfect sphere. Cannon balls are far from perfect. Indeed, the quality control procedures for mass producing nearly identical cannon balls weren't created until the Napoleonic era. As recounted by Alder in his article Making Things the Same, and in his book Engineering the Revolution, it was very difficult to mass produce the perfect spheres assumed by Galileo. It's possible that he had these spheres made especially for him, although the technology to produce a perfect sphere wasn't available until 1729 when the Russian Andrei Nartov made a lathe with the slide rest driven from the main shaft. This discovery is often (and incorrectly) attributed to Henry Maudslay who repeated Nartov's discovery in 1794. Skilled craftsmen such as clockmakers may have had the capability to create such spheres. But could Galileo--or his patron--afford the cost?

Of course, this discussion of tool making may be moot. After all, Galileo fabricated his own telescopes and gave them to nobles as gifts (accompanied, of course, by a copy of his Sidereus Nuncius [see Bagioli's Galileo Courtier]). Why would anyone attack such an obvious expert?

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