Al-Hasan ibn al-Haytham was the first to show that the theory of Euclid and others was wrong, that a ray of light emanates from the eye and falls on the thing seen. He determined the opposite of this theory, that the ray of light emerges from the thing seen and falls on the eye. He inferred from experience and observation that the extension of the light ray is on a line. straight.
Ibn al-Haytham defined transparent bodies, which are those through which light penetrates and the sight can perceive what is behind them, such as air and water. He explained that if light penetrates from one transparent medium to another transparent medium, it deviates from its straightness.
He investigated the refraction of light rays when they penetrate the air surrounding the Earth, and showed that the density of the air in the lower layers is greater than in the upper layers, and that the air does not extend without end, but rather ends at a certain height, so if a ray of light passes through these different air layers density, it slowly breaks and gradually bends towards the Earth's surface.
