ACCIDENTAL Colours are those which depend upon the affections of the eye, in contradistinction to those which belong to light itself. The impressions made upon the eye by looking steadfastly on objects of a particular colour are various, according to the single colour or combination of colours in the object; and they continue for some time after the eye is withdrawn, and give a false colouring to other objects. M. Buffon has endeavoured to trace the connections which these accidental colours have with such as are natural, in a variety of instances. The subject has also been considered by De la Hire and M. Apinus. M. d'Arcy has contrived a machine for determining the duration of those impressions on the eye; and from the result of several experiments, he inferred, that the effect of the action of light on the eye continued about eight thirds of a minute.