The effect of any colour intently viewed, in producing its opposite colour as an ocular spectrum; the efftcts of two colours of the prismatic spectrum, when cast separately into the two eyes at the same time, in producing a compound sensation in the observer; the effects of colours contrasted contiguously in balancing or subduing each other by a similar combination: the like effects of transparent colours in glazing or mixture; the harmonizing influences of colours, and the whole doctrine of equivalence, are all attributable to the same principles.