Treatise on Light

CHAP. I. On rays traveling in a straight line.

That Light is produced by a certain motion. Page 2.
That no physical body passes from the luminous object to our eyes. p. 3.
That Light spreads spherically, and nearly like Sound. p. 4.
Whether Light takes time to spread. p. 4.
Experiment which seems to prove that it passes in an instant. p. 5.
Experiment which proves that it takes time. p. 7.
By how much its speed is greater than that of Sound. p. 9.
In what way the emanation of Light differs from that of Sound. p. 9.
That it is not the same medium that serves for both. p. 10.
How Sound spreads. p. 11.
How Light spreads. p. 12.
Particular remark on the extension of Light. p. 17.
Why Rays only travel in a straight line. p. 19.
How Light, coming from different places, crosses through itself without hindrance. p. 20.

CHAP. II. On Reflection.

Demonstration of the Equality of the angles of incidence and reflection. p. 21.
Why the incident and reflected rays are in the same plane, perpendicular to the reflecting surface. p. 24.
That it is not necessary for the reflecting surface to be perfectly smooth to achieve the equality of the angles of incidence and reflection. p. 25.

CHAP. III. On Refraction.

That bodies could be transparent without any matter passing

through them. p. 27.
Proof that the ethereal matter passes through diaphanousoriginal: "diaphanes." This term refers to substances that allow light to pass through, such as glass or clear water. bodies. p. 28.
How this matter passing through them makes them transparent. p. 29.
That the most solid-looking bodies have a very sparse structure. p. 29.
That Light spreads more slowly inside water and glass than in air. p. 30.
Third hypothesis to explain transparency and the slowing down that Light undergoes there. p. 30.
What can make bodies opaque. p. 31.
Demonstration of why Refraction follows the known proportion of SinesHuygens is referring to what we now call Snell's Law, which mathematically describes how much light bends when entering a new medium.. p. 33.
Why the incident Ray and the refracted ray are produced reciprocally. p. 36.
Why Reflection inside a triangular glass Prism is suddenly reinforced once Light can no longer penetrate it. p. 38.
That bodies causing greater refraction also produce stronger reflection. p. 39.
Demonstration of a Theorem by Mr. de FermatPierre de Fermat (1607–1665), a French mathematician famous for his principle of "least time" in optics.. p. 40.

CHAP. IV. On the Refraction of Air.

That the emanations of Light in the air are not spherical. p. 43.
How, because of this, some objects appear higher than they are. p. 44.
How the Sun can appear on the Horizon before it has risen. p. 45.
That rays of Light become curved in the Air of the Atmosphere, and what effects this produces. p. 46.