Informations and abstract
Keywords: optical-geometrical illusions, history of Italian psychology, discovery of visual illusions, impossible objects, rhetoric of demonstrations.
29 figures are presented and annotated, coming from a book on optical-geometrical illusions which an unknown draftsman, A. Pegrassi, published on 1904. They are divided into anticipations (Ponzo, Tolansky, Künnapas), accidental rediscoveries (Oppel, Müller-Lyer, Judd), similar ways of argumenting (Helmholtz, Thiéry), and originals (at least 36, of which 9 here). The fact is extraordinary, since Pegrassi was acquainted only with a booklet of popular science (Tissandier, 1882), which reported only the figures by Helmholtz (1867). Astonishing the creation of figures almost identical to those of famous scholars, like Müller-Lyer (1889), Brentano (1892) and Judd (1899). It is suggested that careful observation and a good method in creating variants, may lead students of the field to the building up of the same figures.