ACCIDENTAL Colours, are those which depend upon the affections of the eye, in contradistinction to those which belong to the light itself. The impressions made upon the eye by looking steadfastly at 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to the single colour or combination of colours in the object; and they continue for some time after the eye is withdrawn, and give a false colouring to other objects. Mr 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. Epenes; and M. d'Arcy has contrived a machine for determining the duration of the effects of light, and after several trials, finds that it continues about eight thirds of a minute.