It has often been a subject of astonishment to casual speculators that the multitudinous objects of an extensive landscape should be painted with accuracy so extreme, and finish so exquisite, as our every-day experience would seem to prove, upon the small space afforded by the retina of the eye. The truth is, however, that, strictly speaking, only one point can be clearly and distinctly seen by the fixed eye, at a given moment; and all other points included in the vision, are indistinct exactly in proportion to their distance from this central point; and when this distance has increased till the line connecting the two points subtends thirty degrees, the receding point becomes invisible. This distance of thirty degrees, therefore, may be considered as the limit of sight.
