Points, Atoms and Rays of Light: History of a Controversy from Mersenne to Hobbes

Paris, 1635: an interesting mathematical and scientific debate develops within Father Mersenne's circle. The problem concerns the ontological nature of the point and is known as the 'probleme de Poysson', taking its name from Jean-Baptiste Poysson de la Benerie. However, from the epistolary exchanges taking place among the philosophers and scientists involved, we deduce that the true author of the quaestio is Father Mersenne, and this hypothesis seems to be confirmed by the presence of a similar problem in Mersenne's works dated 1625. The topic was widely debated by important philosophers of the time, such as Campanella and Gassendi, and following the traces of this discussion we are able to uncover the history of a controversy which developed from Mersenne to Hobbes. Moreover, on detailed examination of the problem, different aspects and perspectives emerge, which involve not only mathematics and physics, but also optics and the nature of light.