Appendix 27.

(732) [Galluppi and sensation of distant bodies]

At this point I part company with Galluppi. He says that the eye sees distant bodies directly. He likens the tiny units of light successively striking the retina to the different parts of a walking stick felt successively by a hand. But the two facts differ: the hand moves, the eye does not. The length of the walking stick is revealed by movement. If the stick passed over a motionless hand, the hand by itself would not, in my opinion, perceive its length, except possibly through habit and memory. I grant that the eye also senses what is outside itself, but only in so far as the eye is touch; it never senses distance but only something different from itself, or if preferred, something outside itself (because the eye is already felt by the fundamental feeling). This 'outside itself' would indeed be something different from the eye but nevertheless adhering to it.

Galluppi's opinion receives favourable support from the cataract operation performed by the oculist, Giovanni Janin, on a young man. It is also supported by Professor Luigi de' Gregoris' success in restoring partial sight to some people born blind, none of whom, it is said, thought that bodies adhered to their eyes but were things directly seen outside them (cf Delle cateratte de' ciechi nati, osservazioni teorico-chimiche del Professore di chimica e di oftalmia Luigi de Gregoris romano, Rome, 1826). On the other hand Cheselden's experiment is so impressive and so well corroborated that, despite the above evidence, it cannot be immediately refuted. Indeed, the experiment was repeated very carefully in Italy by Professor Jacobi of Pavia and confirmed in every respect.