It is true, that there are individuals whose powers of vision are perfect, in so far as regards the appreciation of light, shade, and configuration, but who are totally incapable of perceiving effects produced by the intermediate phenomenon of colour, every object appearing to them either white, black, or neutral gray; others, who are equally blind as to the effect of one of the three primary colours, but see the other two perfectly, either singly or combined; while there are many who, having the full physical power of perceiving all the varieties of the phenomenon, and who are even capable of making nice distinctions amongst a variety of various colours, are yet incapable of appreciating the æsthetic quality of harmony which exists in their proper combination. It is the same with respect to the effects of sounds upon the ear—some have organs so constituted, that notes above or below a certain pitch are to them inaudible; while others, with physical powers otherwise perfect, are incapable of appreciating either melody or harmony in musical composition. But perceptions so imperfectly constituted are, by the goodness of the Creator, of very rare occurrence; therefore all attempts at improvement in the science of æsthetics must be suited to the capacities of the generality of mankind, amongst whom the perception of colour exists in a variety as great as that by which their countenances are distinguished. Artists now and then appear who have this intuitive perception in such perfection, that they are capable of transferring to their works the most beautiful harmonies and most delicate gradations of colours, in a manner that no acquired knowledge could have enabled them to impart. To those who possess such a gift, as well as to those to whom the ordinary powers of perception are denied, it would be equally useless to offer an explanation of the various modes in which the harmony of colour develops itself, or to attempt a definition of the many various colours, hues, tints, and shades, arising out of the simple elements of this phenomenon. But to those whose powers lie between these extremes, being neither above nor below cultivation, such an explanation and definition must form a step towards the improvement of that inherent principle which constitutes the basis of æsthetical science. Although the variety and harmony of colour which nature is continually presenting to our view, are apparent to all whose visual organs are in a natural state, and thus to the generality of mankind; yet a knowledge of the simplicity by which this variety and beauty are produced, is, after ages of philosophic research and experimental inquiry, only beginning to be properly understood.