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CHAP. XXIII.
Of Optick and Perspective.
NEarest of kin to Geometry, is the Art Perspective. Now Perspective is an Art, that teaches a Three∣fold
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way of seeing Direct, Reflex'd, and Broken: as also the difference of Light, Shadows and Spaces; how Visibles appear through false Intervals, how the beams of the Sun are receiv'd through one or more perspicu∣ous Bodies, and how they play upon several figures of Bodies; the several accidents of Object, Sight, and Me∣dium; and how the Object and the Sight are affected according to the variety of the Medium. Now, as concerning the reason of Seeing, there are sundry and different Opinions. Plato thinks that the sight pro∣ceeds from an equal clearness in the Eye, and the Ob∣ject; the clearness from the Eye, being caus'd by the flowing of the Light to one extrinsick Air; that which proceeds from the Body, being caus'd by a reverbera∣tion of the Sight to the Eye; the middle clearness about the Air, being easily fluid, and apt to receive shape, according to the force of the Sight that always extends it self in a firy Form. Galen agrees with Plato. But Hipparchus saith that the Beams extended from the Eyes to the Bodies themselves, touching them as it were with a certain Palpitation, returns back the apprehension thereof to the Sight. Aristotle is of Opi∣nion, that the Images of things pass from the Object to the Sight according to their quality, through the al∣teration of the middle Air. Porphyrius believes, nei∣ther Beams nor Images, nor any thing else to be the Cause of Sight, but that the Soul knowing her self, ap∣prehends and sees her own self in all visible beings. But the Geometricians and Opticks coming near to Hipparchus, have invented certain Cones made by the co-incidence or falling together of the Beams, which are emitted through the Eyes, so that the Eye appre∣hends many visibles at one time; but those most certain∣ly, where the Beams meet together. But Alchindu• teaches another thing, which St. Austin thinks to be most true, That the Power of the Soul doth act some∣thing
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in the Eye, which is above humane Wisdome to find out. This Art therefore much conduces to the understanding the variety of Coelestial Bodies, their Distance, Magnitude, Motions, and Reflections; and is also a great help to Architecture, in the measuring, adorning, and perfecting great Buildings. But in the Art of Painting and making of Landskips, is of so great use, that neither can be done without it. For it shews us how to make Figures seem undeformed, and in Symme∣try, at whatsoever height or distance they are to be seen.
Of Optick and Perspective.
NEarest of kin to Geometry, is the Art Perspective. Now Perspective is an Art, that teaches a Three∣fold
Page 68
way of seeing Direct, Reflex'd, and Broken: as also the difference of Light, Shadows and Spaces; how Visibles appear through false Intervals, how the beams of the Sun are receiv'd through one or more perspicu∣ous Bodies, and how they play upon several figures of Bodies; the several accidents of Object, Sight, and Me∣dium; and how the Object and the Sight are affected according to the variety of the Medium. Now, as concerning the reason of Seeing, there are sundry and different Opinions. Plato thinks that the sight pro∣ceeds from an equal clearness in the Eye, and the Ob∣ject; the clearness from the Eye, being caus'd by the flowing of the Light to one extrinsick Air; that which proceeds from the Body, being caus'd by a reverbera∣tion of the Sight to the Eye; the middle clearness about the Air, being easily fluid, and apt to receive shape, according to the force of the Sight that always extends it self in a firy Form. Galen agrees with Plato. But Hipparchus saith that the Beams extended from the Eyes to the Bodies themselves, touching them as it were with a certain Palpitation, returns back the apprehension thereof to the Sight. Aristotle is of Opi∣nion, that the Images of things pass from the Object to the Sight according to their quality, through the al∣teration of the middle Air. Porphyrius believes, nei∣ther Beams nor Images, nor any thing else to be the Cause of Sight, but that the Soul knowing her self, ap∣prehends and sees her own self in all visible beings. But the Geometricians and Opticks coming near to Hipparchus, have invented certain Cones made by the co-incidence or falling together of the Beams, which are emitted through the Eyes, so that the Eye appre∣hends many visibles at one time; but those most certain∣ly, where the Beams meet together. But Alchindu• teaches another thing, which St. Austin thinks to be most true, That the Power of the Soul doth act some∣thing
Page 69
in the Eye, which is above humane Wisdome to find out. This Art therefore much conduces to the understanding the variety of Coelestial Bodies, their Distance, Magnitude, Motions, and Reflections; and is also a great help to Architecture, in the measuring, adorning, and perfecting great Buildings. But in the Art of Painting and making of Landskips, is of so great use, that neither can be done without it. For it shews us how to make Figures seem undeformed, and in Symme∣try, at whatsoever height or distance they are to be seen.