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Early History of Optics

Optics, or the study of the behavior and the properties of light, has a long history of investigation, dating back to at least the Egyptians.

The Egyptians, the Assyrians, the Greeks and the Babylonians are all known to have made simple lenses from polished quartz crystals. It is thought that the Emperor Nero was the first monocle-wearer. In his case, it was an emerald, specially shaped, which he supposedly used to watch games in the amphitheater more clearly.

Nevertheless, there were some significant theoretical advances made in the intervening period. As usual, it was the Greeks and Romans who were most prolific in their investigations. Such thinkers as Democritus, Aristotle, Seneca and Ptolemy discovered the straightness of light rays, investigated refraction and considered the curious case of magnification (of objects seen through transparent vessels filled with water).

Some of the main ideas which persisted as a result of existent works was that light somehow emenated from the eye (which Euclid had originally proposed and which Aristotle rejected) and that color was somehow due to the roughness of the atoms of light.

Before the Renaissance, the Islamic world was the custodian of ancient knowledge which they translated, developed and passed on. Chief amongst these was Al-Kindi, who suggested that light rays were emitted from every object and thus permeated the entire world, and Ibn Sahl. The latter was the first to write in detail about the effects of curved mirrors and lenses to bend and focus light.

Important as these two were, they were eclipsed by ‘the father of modern optics’, Ibn al-Haytham, known also as Alhazen. He is associated with two key discoveries, the second of which was proved experimentally (a novelty in itself).. In fact, he has been referred to as the ‘first scientist’ because of his carefully detailed experimental approach. He first insisted that light entered into, and did not emanate from, the eye, overturning the earlier Greek theory.

The second discovery that he proved was that such rays had light and color. In proving this (with use of a camera obscura) he was also able to demonstrate that light moved in straight lines.

In the large body of his work, he not only studied the planets but the anatomy of the eye as well. Needless to say, his work was of great influence when the impetus for scientific investigation returned once more to the West.

The first to really push knowledge of optics forward was Roger Bacon, the English Franciscan. His work showed that he studied the use of convex lenses to magnify small objects. Indeed, he wrote that such lenses could be of use in correcting poor eyesight. (It was an Italian, Salvino D’Amate, who is credited with the first wearable eyeglasses, as opposed to individual lenses, which were held in front of the eye.) Bacon was also the first person to write that perhaps the rainbow was due to the reflection of sunlight from individual raindrops.

Apart from some other theoretical works, there was a general hiatus in terms of significant discoveries which lasted until the time of Johannes Kepler in the early seventeenth century. His interest in astronomy led him to attempt to explain many of the visual effects seen in eclipses and other heavenly phenomena. The result of his work was a book, ‘Astronomiae Pars Optica’ , which is generally thought of as ushering in modern optics by providing a firm foundation for further study. It dealt with many of the major issues, such as parallax, light intensity, reflection (but not refraction), apparent sizes of heavenly bodies and the principle of the pinhole camera.

Refraction was written about in a definitive fashion a few years later by Snellius, after whom the mathematical law of refraction (Snell’s Law) is now named. Decartes, the philosopher, was also investigating the law of refraction (also known as Descartes’ Law) and he was the first to publish the law of reflection, though not the first to discover it.

In the seventeenth century optics generally made great strides. For example, the microscope, most notably under Van Leeuwenhoek, became a more widely used instrument of investigation at one end of the visual scale. At the other, there was the use and development of the telescope, Galileo and Newton being the two giants in this field. Galileo’s telescope was vastly improved by Newton, who developed the refracting telescope

Of course, Newton didn’t stop there. He is also known for using a prism to split white light into its constituent colors.

The several advances of the seventeenth century proved very important in the way research was subsequently carried out, and is a good place to end this very brief survey of the early history of optics. As we move nearer to modern times, so the various theories of light come more to the fore, particularly with the quantum theories and the investigations of photons. By leaving the history at this point, we are better able to see the slow progression of understanding which allowed the more startling modern theories to develop.