The Image and the Moving Eye: Jean Pélerin (Viator) to Guidobaldo del Monte

HE THEORY of perspective continues, even in our own day, to provide matter for debate.' The present paper considers the late fifteenthand sixteenth-century analyses of the Albertian construction, which were carried out in terms of medieval theories of the physiology of vision. By examining the work ofJean Pdlerin (Viator) and his successors in the light of the tradition of optics, we can see the internal coherence of their arguments and arrive at a clearer conception of the problems which they were attempting to solve. In particular, this approach allows us to recognize and give due importance to the distinction that was made between the perspective used in constructing a picture and the beholder's visual perception of the result. An image constructed in accordance with the rules of linear perspective always has a centric point, that is, a point at which the orthogonals converge. The position of this point defines the line of sight of the beholder. The distance point determines the exact position of the eye on this line, the position from which the picture will reveal the spatial ordering of its components.2 The system of perspectiva artificialis, using a single centre ofprojection, is first described in Leon Battista Alberti's De pictura.3 Alberti justifies his construction by an appeal to optics, that is, to the geometry of the pyramid of vision as described in the optical treatises of antiquity. His two major sources are Galen and Euclid. Alberti's account of the eye is freely paraphrased from Galen's De usu partium:4 extrinsic rays (radii