Typing that I wonder where I heard it or even if it's true. Nevertheless, reading in Against Method today makes it clear to me that Foucault should have been a big fan. There's a great section where Feyerabend is discussing early uses of the telescope -- the book is preoccupied with the history of science -- and the fact that there was much disagreement about its accuracy. He turns then to the problem of Galileo's drawings of the moon. "It needs only a brief look at Galileo's drawings, and at photographs of similar phases to convince the reader that 'none of the features recorded... can be safely identified with any known markings of the lunar landscape.'" Feyerabend acknowledges the possibility that Galileo simply did a bad job translating what he saw to paper, but notes, "I rather doubt it in view of the quite extraordinary observational skill which Galileo exhibits on other occasions."
Seeking a better explanation, Feyerabend goes on to entertain two possibilities. The first, that Galileo was merely recording the imperfections of the early telescopes, their distortion, is only mildly interesting. The second, however, is a real mind-opener:
Hypothesis II, just like Hypothesis I, approaches telescopic reports from the point of view of the theory of perception; but it adds that the practice of telescopic observation and acquaintance with the new telescopic reports changes not only what was seen through the telescope, but also what was seen with the naked eye. It is obviously of importance for our evaluation of the contemporary attitude towards Galileo's reports.The effect of this second hypothesis, which is clearly the one that Feyerabend favors for polemical reasons, is to recast the theory of perception as the history of perception or, to be more precise, to demonstrate how theory is always already historical and that to think otherwise is an example of severe ideological closure. Personally, I love the idea that what we can all plainly see is a function of our place in history.
That the appearance of the stars, and of the moon, may at some time have been more indefinite than it is today was originally suggested to me by the existence of various theories about the moon which are incompatible with what everyone can plainly see with his own eyes. Anaximander's theory of partial stoppage (which aimed to explain the phases of the mooon), Xenophanes' belief in the existence of different suns and different moons for different zones of the earth. Heraclitus' assumption that eclipses and phases are caused by the turning of the basins, which for him represented the sun and the moon -- all these views run counter to the existence of a stable and plainly visible surface, a "face" such as we "know" the moon to possess.