  In 1925 Sir James Jeans calculated that a star made up of an ideal gas,
generating energy as a moderately positive function of temperature and density,
could not exist. Such stars would be unstable to oscillations of increasing
size. It appears that the flaw in his calculation has never been clearly
explained, especially the physical basis for it. I conclude it lies in an
almost offhand assumption made about the form of the temperature perturbation.
The episode has lessons concerning the structure of stars, the use of
perturbation methods (especially in discussing stability), the use of
mathematical models and the process by which one theory is chosen over its
competitors.
