Aguilon, François D’

(b. Brussels, Belgium, 1546; d. Antwerp, Belgium, 1617)

physics, mathematics.

The son of the secretary to Philip II, Aguilon became a Jesuit in 1586. After having taught syntax and logic, then theology, he was charged with organizing in Belgium the teaching of the exact sciences, which were useful in commerce, geography, navigation, and architecture, as well as military activities. This project led to the composition of a master treatise on optics that synthesized the works of Euclid, Ibn al-Haytham (Alhazen), Vitellion, Roger Bacon, Pena, Ramus (Pierre de la Ramée), Risner, and Kepler. Its organization into three sections was determined by the manner in which the eye perceives objects (directly, by reflection on polished surfaces, and by refraction through transparent bodies). Aguilon’s death prevented the publication of the second and third sections, on catoptrics, dioptrics, and telescopes. Only the first part exists, with six frontispieces drawn by Rubens: Francisci Aguilonii e Societate Jesu Opticorum libri sex juxta ac mathematicis Wiles (1613).

Aguilon treated, successively, the eye, the object, and the nature of vision; the optic ray and horopter; the general ideas that make possible the knowledge of objects; errors in perception; luminous and opaque bodies; and projections.

The sixth book, on orthographic, stereographic, and scenographic projections, remains important in the history of science. It accounts for a third of the treatise and was meant for the use of astronomers, cosmographers, architects, military leaders, navigators, painters, and engravers. It places particular emphasis on stereographic projection—a type of projection, used by Ptolemy, in which the portion of the sphere to be represented is projected from the pole onto the plane of the equatorial circle.

The balance of the treatise is of interest for the history of optics: description of the eye; controversies on the nature of light and its action; the application of mathematics to optics; the analysis of the concepts of distance, quantity, shape, place, position, continuity, discontinuity, movement, rest, transparency, opacity, shadow, light, resemblance, beauty, and deformity; and explanation of the various errors of perception linked to distance, size, position, shape, place, number, movement, rest, transparency, and opacity.

Book 5, in spite of an Aristotelian concept of light, studies the propagation of light, the limit of its action, the phenomena produced by the combinations of light sources, and the production of shadows. Aguilon proposes an experimental apparatus, drawn by Rubens, that made it possible to study the variations of intensity according to variations in distance and to compare lights of different intensities. This attempt to apply mathematics to the intensity of light was continued by Mersenne, then by Claude Milliet de Chales, and resulted in Bouguer’s photometer.

BIBLIOGRAPHY

Aguilon’s only work is Francisci Aguilonii e Societate Jesu Opticorum libri sex juxta ac inathematicis utiles (Antwerp, 1613: Wurzburg, 1685; Nuremberg, 1702).

Writings on Aguilon or his work are P. Alegambe, Bibliotneca scriptorum Societatis Jesu (Antwerp, 1643), p. 112: A. de Backer, Bibliotheque des écrivains de la Compagnie de é (Liege, 1853); Michel Chasles, Apereu historique sur l’origine et le developpement des methodes en geometrie (Brussels, 1837), pp. 222. 517; F. V. Goethals, Histoire des lettres, des sciences et des arts en Belgique et daps les pays limitrophes, I (Brussels, 1840), 149, 153; J. E. Morère, “La photomètrie: Les sources de l’Essai d’optique sur la gradation de la lumière de Pierre Bouguer, 1729,” in Revue d’histoire des sciences, 18 , no. 4 (1965), 337–384; L. Moréri, Dictionnaire historique (Paris, 1749), 1, 231; V. G. Poudra, Histoire de la perspective ancienne et moderne (Paris, 1864), pp. 68–70; Adolphe Quetelet, Histoire des sciences mathématiques chez les Belges (Brussels, 1864), pp. 192–198: E. Quetelet, “Aíguillon” [sic], in Biographie nationale, I (Brussels, 1866), 140–142; and C. Sommervogel, Bibliothèque de la Compagnie de Jésus, I (Louvain, 1890), 90.

J. E. MorÈre