Becquerel's experimental mistakes

Abstract: In 1896, Henri Becquerel detected a penetrating radiation emitted by some uranium salts and met a phenomenon that nowadays we call “radioactivity”. Becquerel’s study of uranium radiation was not casual or blind. It was guided by his acceptance of Poincaré’s conjecture concerning a possible relation between X rays and luminescence. What Becquerel expected to find was the emission of a penetrating electromagnetic radiation (something similar to ultraviolet rays) emitted by a special phenomenon of fluorescence or phosphorescence that violated Stokes’ law. Guided by his preconceptions, Becquerel described experiments that seemed to support the view that uranium radiation had the usual properties of known electromagnetic waves: reflection, refraction and polarization. He also described an increase in the emission of radiation when uranium compounds were stimulated by sunlight. Those and several other aspects of Becquerel’s experimental work must nowadays be interpreted as experimental mistakes. Becquerel’s mistakes were gradually corrected by other researchers. As the study of radioactivity developed, Becquerel reinterpreted his own early work, hiding his mistakes or ascribing to himself their correction. The aim of this article is to discuss one particular episode of experimentation – Becquerel’s study of the phenomenon we call radioactivity – and the methodological problems aroused by his mistakes.

Keywords: radioactivity; experimental errors; history of physics; Becquerel, Henri