Now, if the attention be fixed exclusively on the central point, the surrounding points, being indistinct directly as their distance, will, near the limit, be barely visible; consequently the limit will not be a harsh line, but, on the contrary, will be soft and unfelt by the eye. But this is a mode of vision very rarely employed by the eye in contemplating landscape. We prefer receiving all the visual rays partially, to receiving one perfectly; and, instead of confining the attention to the central point, distribute it *[This operation is partly optical, partly mental. Optical, inasmuch as a slight change takes place in the form of the eyeball; mental, because ideas which the optic nerve was not before permitted to convey to the brain, are now permitted to take their full effect.], as nearly as may be, over the whole field of vision. Partial distribution is usually and instinctively effected; perfect distribution only occasionally, when we wish to become aware of a general effect. The more general the distribution, the more severe the limit; and when the distribution is perfect, the limit is a circle, whose diameter subtends sixty degrees, whose centre is opposite the eye, and whose area is a section of the cone of rays by which the landscape is made sensible to the eye.
