The nature of light on opaque and transparent bodies

Opaque, transparent, and glossy bodies

Solid bodies are of two natures, opaque and transparent, each yielding two effects: opaque with and without gloss, transparent with and without gloss. Crystal is transparent with gloss when not worked to a rough surface, which takes only the quantity of light and not the figure of the illuminant, so that rays passing through leave no image of the illuminant on the surface.

On an opaque body the rays stop at impact

The opaque is that through which the luminous rays that strike it cannot penetrate; they remain at the site of impact and illuminate as much as they touch. That part is more luminous which is struck by a greater sum of rays, and conversely less luminous where fewer rays reach it.

Illumination of spherical bodies

The surface of an opaque spherical body is lit in two ways: one part sees the whole circle of the luminous body, the other lacks part of that circle. The part that sees the whole circle is itself circular; the part not seeing it whole is circular-parallel. The sun sends rays through the universe, and the object that breaks them fastens them to itself.

Nearer the light, the greater the variety

At the letters m, n, a, e the parts of the illuminated body make the greatest variety of light. The nearer the luminous body is to the illuminated one, the greater are the differences of light it receives, and these are infinite and imperceptible at their boundaries.

Continuous quantity divisible to infinity

Because every continuous quantity is divisible to infinity, the line n m and the place o p are continuous quantities. Where its rays strike from o to p, that site, through its curvature, loses at every degree of its length degrees of the luminous body.

Conception: straight rays and how much of the source is seen

All luminous rays that pass through equal space are straight. The part of an object nearer the light is lit by a lesser sum of rays but more powerful light; the whole object that sees the light is seen and lit by it; and that is more illuminated which sees a greater quantity of the luminous body.

Colonna destra.

Variante per il brano precedente al richiamo +:

Nel margine, figura di triangolo:

Figure di raggi luminosi.

Colonna sinistra:

Due figure di raggi luminosi:

Figura di luminoso e illuminato colle lettere:

Sotto il precedente e sopra una figura di raggi luminosi:

Sul margine figura di luminoso e illuminato colle lettere:

Angolo inferiore sinistro.

A destra del precedente:

Right column.

Variant for the preceding passage at the mark +:

In the margin, figure of a triangle:

Figures of luminous rays.

Left column:

Two figures of luminous rays:

Figure of luminous and illuminated body with the letters:

Below the preceding and above a figure of luminous rays:

In the margin, figure of luminous and illuminated body with the letters:

Lower left corner.

To the right of the preceding: