LETTER II.. The Eye the Most Important of Our Organs--Popular Description

The eye the most important of our organs--Popular description of it--The eye is the most fertile source of mental illusions--Disappearance of objects when their images fall upon the base of the optic nerve--Disappearance of objects when seen obliquely--Deceptions arising from viewing objects in a faint light--Luminous figures created by pressure on the eye, either from external causes or from the fulness of the blood-vessels--Ocular spectra or accidental colours--Remarkable effects produced by intense light--Influence of the imagination in viewing these spectra--Remarkable illusion produced by this affection of the eye--Duration of impressions of light on the eye--Thaumatrope--Improvements upon it suggested--Disappearance of halves of objects or of one of two persons--Insensibility of the eye to particular colours--Remarkable optical illusion described 8