Smooth Motions

In connection with Don’s points about philosophy-as-therapy I want to address (hopefully in the seminar today) the issue of Epicurus’ apparent willingness to craft or cast the results of natural science such that its explanations promote tranquility, regardless of their accuracy, certainty, and possibly even truth, and the effect that might have on scientific knowledge.

I recently gave a talk before the UCSD philosophy department colloquium about mathematical explanations of natural phenomena in Aristotle. One of my key examples was Aristotle’s explanation of solar and lunar halos. It is a great chapter in his Meteorology (3.1-3) and indeed in the history of science. It contains one of the earliest, and possibly the earliest, lettered diagram in the history of Greek science and mathematics. Aristotle explains that the halo, along with sundogs and rods, as well as the rainbow, is some kind of optical phenomenon due to the “reflection” of optical rays in the tiny mirrors in the atmosphere between the luminescent body and the observer. As a purely optical phenomenon, the halo appears the same to all those to whom it appears, unlike a cloud or any soid body or substance, which looks different from different perspectives. This accords nicely with modern explanations of the phenomenon, according to which randomly arrayed hexagonal ice crystals refract light at 22 degrees on a plane between the moon and an observer.

Now consider Epicurus’ explanation of the same phenomenon in his Letter to Pythocles:

The halo around the moon is produced because air from all sides moves towards the moon; or when it evenly restricts [the movement of] the effluences sent off from it to such an extent that this cloudlike phenomenon forms around it in a circle and is not interrupted in the slightest extent; or it restricts [the movement of] the air around it symmetrically on all sides so that what is around it takes on a round and dense formation. And this happens in certain parts either because a certain effluence forces its way from outside or because heat occupies passages suitable for the production of this effect. (Pyth. 110-111, trans. Inwood)

Relative to Aristotle’s mathematical and optical account of the same phenomenon, this is a very lame explanation. Perhaps it would be good enough to relieve suffering, if I was afraid that lunar halos were a menacing sign from an interventionist god. But it is retrograde science. Epicurus does not even avail himself of Aristotle’s as one of the alternative explanations of the phenomenon, even though he should want as many as are plausible. He seems to be cribbing from some earlier meteorological work, perhaps by Anaximines, which explains such phenomena in terms of compression and rarefaction of air. Unfortunately, Lucretius does not deal with the problem, either.