The Iraqi born Ibn al-Haytham was a giant of Arabic science. He is credited with inventing the scientific method because of his detailed and precise method of experimentation and recording of proofs. His most important work was the Book of Optics (Kitab al-Manazir) written in Cairo, when he was under a type of house arrest for disappointing the ruler of the country for failing to solve the poisoned challenge of taming the Nile River’s flooding.
He also carried out the first experiments on the dispersion of light into its constituent colours and studied shadows, rainbows and eclipses; and by observing the way sunlight diffracted through the atmosphere, he was able to work an estimate for the height of the atmosphere, which he found to be around 100km.
When the Book of Optics (Kitab al-Manazir) by 11th century scientist and scholar of optics, Ibn Al-Haytham (Alhazen in Latin) was translated from Arabic into Latin it created a sensation among European scholars interested in the study of light, physics and optics. By 1571 the book was in print, but earlier editions and handwritten translations of large parts of it were appearing in England by the 13th century, where Roger Bacon began a translation of the work.
The key principle to Al-Haytham’s observations is that light travels in straight lines. Thus in Chapter 2 of his book, he writes:
تمييز خطوط الشعاع
قد تبين في المقالة الأولى أن خطوط الشعاع التي من سموا يدرك البصر المبصرات هي الخطوط المستقيمة
التي تلتقي أطرافها عند مركز البصر
Distinguishing the lines of light beams
It is known from the first chapter that light beams are received as straight lines.
They converge at the edges of sight and center on the pupil of the eye.
Newton’s method of experimentation in dark rooms using the principle of Al-Haytham’s camera obscura is revealed in Isaac Newton, A Letter of Mr. Isaac Newton…containing his New Theory about Light and colors. Philosophical Transactions of the Royal Society, No. 80 (19 Feb. 1671/2), pp. 3075-3087. In that letter Newton describes his method.
And in order thereto having darkened my chamber, and made a small hole in my window-shuts, to let in a convenient quantity of the Suns light, I placed my Prisme at his entrance, that it might be thereby refracted to the opposite wall. Isaac Newton Letter, 19 Feb. 1671/2