The oversimplification of issues in the history of science leads to a misunderstanding of the nature of scientific progress. For instance, most texts and many histories of science have perpetuated the myth that the distinction between Newton's theory of light and that of Huygens was clear cut and simple. They have compounded their error by indicating that Foucault's experiment in 1850, where he found the speed of light to be slower in water than in air, was “crucial” evidence in favor of Huygens's theory, thereby “disproving” the corpuscular theory of Newton. The position is defended that the theories of Newton and Huygens did not represent simple opposites; Newton's theories on light have been frequently misrepresented; and Foucault's experiment was not a crucial one.