Abstract

Knowledge of residual perturbations in the orbit of Uranus in the early 1840s did not lead to the refutation of Newton's law of gravitation but instead to the discovery of Neptune in 1846. Karl Popper asserts that this case is atypical of science and that the law of gravitation was at least prima facie falsified by these perturbations. I argue that these assertions are the product of a false, a priori methodological position I call, 'Weak Popperian Falsificationism'. Further, on the evidence the law was not prima facie false and was not generally considered so by astronomers at the time. Many of Popper's commentators presuppose WPF and their views on this case and its implications for scientific rationality and method suffer from this same defect.