Belgian optician and mathematician who coined the term "stereoscopic." A Jesuit priest whose family was of Spanish descent, d'Aguilon studied persistence of vision and visual illusions, and in 1613 published his Opticorum. This work contained a discussion of stereoscopic projection, the phenomenon whereby a person's two eyes capture and integrate images viewed from slightly different angles, thus giving the image greater depth. Knowledge of stereoscopy—which had been recognized but unnamed since the time of Greek astronomer Hipparchus (c. 190-c. 120 b.c.)—would prove useful in the development of binoculars and, much later, photography.