History of Optics PHY 108 Fall 2003

Early “Optics”

“In the beginning God created the heaven and the earth. Now the earth was unformed and void, and darkness was upon the face of the deep; and the spirit of God hovered over the face of the waters. And God said: ‘Let there be light.’ And there was light.” Or consider this alternative translation: “When God began to create the heavens and the earth, while the earth was unformed and void, and darkness was on the face of the deep, and the spirit of God hovered over the face of the waters, God said, ‘Let there be light.’ And there was light.”

History of Optics – Early Players Aristotle (4 th cent. BC) Euclid (Alexandria, ca. 300 BC) Ptolemy (2 nd cent. AD)

History of Optics – Early Ideas Straight-line propagation Equal-angle reflection Bending of rays at interfaces (“refraction”) Vision theories –Objects-to-eye (intromission) –Vision as a “feeling process” (extramission)

History of Optics Euclid (Alexandria, ca. 300 BC) - “Optics” Early record of the principle that rays of light travel in straight lines. Wrote about measuring the relative apparent size of objects by referring to the “angular size.” (A precursor to perspective?) His theory of vision considered rays of light emanating from the eyes of the observer.

Euclid A student learned the first proposition in geometry from Euclid’s “Elements” and wanted to know what he would gain by learning these things. Euclid called his slave and said disdainfully, “Give this student a coin since he has to make a profit from what he learns.”

History of Optics First military applications of optics Archimedes and the siege of Syracuse (214 B.C.)

Archimedes The Syracusans finally lost to the Romans, and Archimedes was killed by a Roman soldier (because he refused to quit working on a geometrical proof when commanded to do so!?). Apparently, Archimedes had only disdain for his engineering and practical achievements, never even bothering to write them down. For him, pure knowledge (geometry, for example) was the only worthwhile pursuit.

Siege of Syracuse

Ptolemy Ptolemy (2nd century AD, also Alexandria) - Of his works, only an incomplete 12th century Latin translation survives, which in turn is based on a lost Arabic translation. The title “Almagest” derives from the Arabic version of the Greek superlative meaning “The Great.”

The “Dark Ages” Many Greek works were lost to western Europe for several centuries (ca AD). Most works survived only in Arabic translations; the scientific culture thrived in Baghdad and other centers of the Islamic world (ca AD).

Islamic Contributions Abū Y ū suf Ya’q ū b ibn Ishāq Al-Kindī (Baghdad, ca. 850) Studied Euclid, others; worked to integrate the Greek/Neo-Platonic traditions with Islam. Hunayn ibn Ishāq (Baghdad, ca. 850) Anatomy and physiology of the eye. Ibn Sahl – (ca. 980) Calculation of the correct lens shape needed to focus the sun’s rays to a perfect point. Abū Alī al-Hasan ibn al-Haytham (Basra, Cairo, ca. 1000) Put to rest idea of visual rays; understood many optical principles, such as the “camera obscura.” Synthesized all optical knowledge.

Eyeglasses? When do eyeglasses first appear? Roger Bacon? (13th century) Umberto Eco’s “The Name of the Rose” Principles were not understood, however.

Kepler (ca. 1600) Solves the Problem He was the first to theoretically understand how images are formed by lenses. Kepler still did not have an exact mathematical formula to describe the phenomenon, however. Museum der Sternwarte Kremsmünster, Austria

Art and Science Albrecht Dürer