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blue vault, whose diameter is that of the visible horizon; which the sun, moon, and stars seem equally to touch at their rising and setting. Hence the notion of these luminaries setting in, and rising from the ocean has universally prevailed through all nations: and it has not been by the evidence of improved sense; but by the calculations and discoveries of improved intellect, that the error has been removed.

4. The visible magnitude of bodies depending entirely upon their distance from the eye, we have, of course, as imperfect and inadequate perceptions of it from the unaided sense of vision, as we have of distance. The pen, which I hold between my fingers, occupies a greater space in the retina, when only a foot from the eye, than the spire of Salisbury does, when seen at the distance of a mile; and, coɔnsequently, as far as concerns the mere organ of sense, is bigger: for though the real magnitude of an object, which is perceived by a computation of its distance, rendered instantaneous by habit, may affect the imagination, the visible dimensions of it alone are impressed upon the eye; and, consequently, can alone affect the sensation excited.

5. Hence we may learn how to estimate the theory of an eminent writer, who supposes that objects of large dimensions are sublime,

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because the great number of rays, which they emit, crowd into the eye together, or in quick Of Sight succession, and produce a degree of tension in the membrane of the retina, which, approaching nearly to the nature of what causes pain, must (in his own words) produce an idea of the sublime*. But, to say nothing of this assumed connection between the causes of pain and the ideas of the sublime, the slightest knowledge of optics would have informed him that the sheet of paper, upon which he was writing, being seen thus close to the eye, reflected a greater, and more forcible mass of light; and, consequently, produced more irritation and tension, than the Peak of Teneriffeor Mount St. Elias would, if seen at the distance of a few miles:-yet, surely he would not say that the sheet of paper excited more grand and perfect ideas of the sublime.

6. That the irritation, produced in the mem branes of the eye by vision, is proportioned to the quantity of light poured into it, we may perceive by the dilation and contraction of that membrane called the iris; which always expands its circle, as the quantity of light, to which it is exposed, is diminished, and contracts it, as it is increased. In the eyes of animals formed to see with a very small quan

Sublime and Beautiful, Part IV. f, ix.

tity of light; such as cats, owls, &c. this power is very great; and the membrane affected seems to consist of valves, which open and shut, instead of a sphincter, that dilates and contracts. Hence, in the night, when these valves are entirely open, the eyes of these animals present a very singular appearance of large luminous circles; which, in the day, are reduced to small horizontal slits; through which the few rays, that they then want, are suffered to pass: for, to organs of such nice sensibility, any great quantity would be painful; and it is probable that the degree of irritation alone regulates the opening and shutting of the membranes, which admit and exclude it, in the same manner as it does the dilation and contraction of the corresponding membranes in our eyes, without the intervention of the will.

7. The pains and pleasures of vision, however, like those of the other senses, depend upon the modes as well as degrees of irritation; for all the different colours may be properly considered as different modes, in which light acts upon the eyes; colours being only collections of rays variously modified, separated, and combined, according to the different textures of the surfaces of the bodies, from which they are reflected, or the substances of those through which they are refracted,

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s. There are, indeed, scarcely any human eyes of such extreme sensibility, unless in a morbid state, as to feel any absolute pain from colours composed of reflected rays: for unless the reflection be from the surface of a concave mirror, in which the rays are collected and condensed, the effect of light is necessarily weakened by being reflected; whence the refracted colours of a prism or a rainbow are always more vivid and bright than those which are reflected from any opaque substance. There are, however, some kinds of birds and quadrupeds, such as turkeys and oxen, to whom scarlet is evidently painful; as they will run at it, and attack it with the utmost virulence and fury. Green, on the contrary, appears to be grateful to the eyes of all animals; though colours, as well as sounds and flavours, are more pleasing when harmoniously mixed and graduated, than when distinct and uniform. Indeed, they almost always are graduated and broken in nature: for, though an object be of one colour throughout, unless it present one equal superficies to one equal degree of light, that colour will be variously graduated and diversified to the eye by every undulating or angular projection or indenture of its form. In every individual pink or rose, whether its colour be white, yellow, or red,

there are infinite varieties and gradations of tint, produced, not only by the different degrees and modifications of light and shadow, but by the various reflected rays, which one leaf casts upon another, according to their dif ferent degrees of opacity and exposure.

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9. When many sorts and varieties of these rich and splendid productions of nature are skilfully arranged and combined, as in the flower-pots of Vanhuysum, they form, perhaps, the most perfect spectacle of mere sensual beauty that is any where to be found. The magnificent compositions of landscape are, indeed, spectacles of a higher class; and afford pleasures of a more exalted kind: but only a small part of those pleasures are merely sensual; the venerable ruin, the retired cottage, the spreading oak, the beetling rock, and limpid stream having charins for the imagination, as well as for the sense; and often bringing into the mind pleasing trains of ideas besides those, which their impressions upon the organs of sense immediately excite. As far, however, as they do afford sensual pleasure, it depends upon the same principle as the pleasures of the other senses already treated of; that is, upon a moderate and varied irritation ✓ of the organic nerves for, if the irritation be too strong; that is, if the transitions of colour be too violent and sudden, and the oppositions

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