Who Placed the Eye in the Center of a Sphere? Speculations about the Origins of Thomas Reid's Geometry of Visibles

Abstract

Thomas Reid argued that the geometrical properties of visible figures equal the geometrical properties of their projections on the inside of a sphere centred around the eye. In recent scholarship there are only a few suggestions of which sources might have inspired Reid. I point to a widely ignored body of early eighteenth-century literature – introductions into projective geometry, the use of celestial globes and astronomy – in which the model of the eye in the centre of a sphere was immensely popular. Moreover, I argue that Reid's account results naturally from some astronomical doctrines in conjunction with George Berkeley's theory of vision.