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Nature, Experiment, and the Sciences: Essays on Galileo and the History of Science in Honour of Stillman Drake (Boston Studies in the Philosophy of Science)

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This collection in honour of Stillman Drake brings out some of his most devoted groupies. A particularly striking example is MacLachlan's article "Drake against the philosophers."

"Galileo as philosopher." MacLachlan hates philosophy, as witnessed by the title of his article, and wishes to dismiss any and all philosophically inclined readings of Galileo. This stance is complicated by the fact that "Galileo considered himself a philosopher" and asked the Duke if "in addition to the title 'mathematician' His Highness will annex that of 'philosopher'; for I may claim to have studied more years in philosophy than months in pure mathematics." (p. 125). MacLachlan tries to resolve this problem not by actually investigating what Galileo meant by "philosopher" but by arguing that Galileo could not possibly have meant anything like what we mean since he was often in disagreement with various philosophers: "The puzzle is how could one engaged in a lifelong battle with philosophers ask specifically to be numbered among them?" (p. 125). What a puzzle indeed! A philosopher who disagrees with other philosophers?! Who has ever heard of such a thing?

"Galileo and the law of inertia." "Please! No more Galilean 'circular inertia'" (p. 132), pleads MacLachlan. No wonder he ends up on his knees, for his argument is based on an elementary error of logic: to prove that Galilean circular inertia is a myth he points to a few passages where Galileo is alluding to rectilinear inertia. This of course proves nothing. Galileo asserted the law of circular inertia, which is a law of the form: if something is moving in a circle then so-and-so. Whatever Galileo may have asserted elsewhere about things moving in straight lines---whether it be that they keep moving at the same speed, or turn blue, or explode---obviously does not affect the law of circular inertia in any way whatsoever. Let me make a further point on the inertia issue. To prove that Galileo advocated rectilinear inertia, MacLachlan refers to a passage regarding canon ball trajectories. Galileo says: the projectile would go in a straight line, only gravity pulls it down, so the path is a parabola, etc. QED: rectilinear inertia, not circular, right? Not so. Consider another experiment: swinging a ball on a string in a circle. If you let go the ball flies off on a tangent; it does not continue in its circle as circular inertia would dictate. Does this disprove circular inertia? No. To defend circular inertia one would simply have to argue that the force exerted via the string is much stronger so that circular inertia becomes unnoticeable (after all, one cannot disprove gravity by pointing to two rocks that are lying still instead of smashing into each other, for example). Now, if even a feeble string is enough to put circular inertia out of play, then we should surely not expect it to be unperturbed by the force of a firing canon.

"The structure and purpose of Galileo's Dialogue." Traditional history has it that Galileo made a fool of himself by developing a stupid theory of the tides and using it as his main proof of the earth's motion. MacLachlan says: No, "the Dialogue was originally structured to account for the tides...---not as a final clincher [for] the Copernican world view" (p. 139), but the censors meddled with it, "which, I believe, gave the Dialogue a stronger Copernican cast than Galileo had originally intended" (p. 137). For some reason MacLachlan neglects to draw the obvious conclusion from his own argument: "Galileo's courage" (p. 142) was enough to write an entire book devoted to an idiotic theory, but he was too much of a coward to ever support Copernicus in print.