Huygens at work: Annotations in his rediscovered personal copy of Hooke's Micrographia

Summary

It is well known that Hooke's wave theory of light, set forth in his Micrographia of 1665, is viewed as a step towards Huygens's famous theory of light. This view depends mostly on some short remarks given by Huygens in his Traité de la Lumi`ere (1690) and the earlier Projet du Contenu de la Dioptrique (1673). Huygens's personal copy of Micrographia was believed to be lost until found at Braunschweig (Brunswick) University Library by the author three years ago. It is annotated at Observ. IX (pp. 47–67) only, where Hooke deals with his wave theory of light and colours. This article provides a short review of Hooke's theory, and an interpretation of Huygens's annotations, which show clearly the first steps towards the opinions he was to express in his Traité de la lumi`ere, particularly methodological ones. Furthermore, a short comparison is here drawn with Huygens's annotations in his copy of Ango's L'optique divisée en trois livres, which show similar patterns of reasoning.