Experimentum crucis

Abstract

Chronology 1620 Instantice Crucis as introduced by Bacon 1648 Uni-coloured rays sent through prisms (Marci) 1665 Colour dispersion behind pinholes (Grimaldi) 1665 Hooke coins the phrase Experimentum Crucis 1 666- Newton dissects sunrays with prisms and pinholes 1672 Newton publishes an Experimentum Crucis 1672- Controversies about the experiment 1681 Mariotte rejects it 1704 Is there any Experimentum Crucis in the ? 1715- Desaguliers exhibits variants o f the experiment 1722 A Paris edition o f the Opticks. Its prefaces 1722 A final substitute (?) for the Experimentum Crucis Introduction From 1666 onwards Newton planned and executed a great variety of prism experiments, but in his celebrated treatise about ‘Light and Colors’ (1) he described only three of them. If we trust in Newton’s ‘historicall narration’ (2) his curiosity was first aroused by the oblong shape of the solar image, which according to traditional geometrical optics should have been circular . Newton said that he figured out several hypotheses to account for this anomaly, and by removing these ‘suspitions’ systematically he was led to an Experimentum Crucis , which proved ‘that Light consists of Rays differently refrangible’. His narrative seems to imply that he carried out the whole investigation within a few sunny days in spring 1666.