Les mires méridiennes lointaines de l’Observatoire de Lyon : Recherches bibliographiques, archivistiques et archéologiques

Abstract

The first argument set out in 1877 by the Parisian astronomer Charles André, founder of the Observatoire de Lyon, to justify the establishment of an astronomical institute in Saint-Genis-Laval was the fact that it offered the opportunity to install remote marks along its meridian. André had used this argument three years before to reject another site selected by a local committee. However, at that time remote meridian marks had been abandoned by most astronomers in favour of close ones. We have conducted field research to discover the remains of these marks, as well as to seek evidence – both in the literature and in archives – of their use. This investigation shows that the argument for remote marks was in fact driven by geodetic considerations. The choice of Saint-Genis-Laval was actually made by geodesists of the Dépôt Général de la Guerre and its director, François Perrier, who wanted to institute new observatories in Province as key points in the primary geodetic network of France.