There are four sources of pleasure attendant on the excitation of the nerves of vision by light and colours, besides that simply of perception above mentioned; the first is derived from a degree of novelty of the forms, colours, numbers, combinations, or successions, and visible objects. The second is derived from a degree of repetition of their forms, colours, numbers, combinations, or successions. Where these two circumstances exist united in certain quantities, and compose the principal part of a landscape, it is termed picturesque by modern writers. The third source of pleasure from the perception of the visible world may be termed the melody of colours, which will be shown to coincide with melody of sounds: this circumstance may also accompany the picturesque, and will add to the pleasure it affords. The fourth source of pleasure from the perception of visible objects is derived from the previous association of other pleasurable trains of ideas with certain forms, colours, combinations, or successions of them. Whence the beautiful, sublime, romantic, melancholic, and other emotions, which have not acquired names to express them. We may add, that all these four sources of pleasure from perceptions are equally applicable to those of sounds as of sights. I. _Novelty or infrequency of visible objects._ The first circumstance, which suggests an additional pleasure in the contemplation of visible objects, besides that of simple perception, arises from their novelty or infrequency; that is from the unusual combinations or successions of their forms or colours. From this source is derived the perpetual cheerfulness of youth, and the want of it is liable to add a gloom to the countenance of age. It is this which produces variety in landscape compared with the common course of nature, an intricacy which incites investigation, and a curiosity which leads to explore the works of nature. Those who travel into foreign regions instigated by curiosity, or who examine and unfold the intricacies of sciences at home, are led by novelty; which not only supplies ornament to beauty or to grandeur, but adds agreeable surprise to the point of the epigram, and to the double meaning of the pun, and is courted alike by poets and philosophers. It should be here premised, that the word Novelty, as used in these pages, admits of degrees or quantities, some objects, or the ideas excited by them, possessing more or less novelty, as they are more or less unusual. Which the reader will please to attend to, as we have used the word Infrequency of objects, or of the ideas excited by them, to express the degrees or quantities of their novelty.