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Retrospect

The light of the genius

Optics, by Newton, completes 300 years just as important as when it was published

The fascination that light has always exerted on man earned its best translation 300 years ago. The English physicist Isaac Newton (1642-1727) published, in 1704, Optiks: or, a treatise of the reflexions, refractions, inflexions and colours of light . The book was a watershed for optics. “After its publication, it was possible to find a plausible explanation for the majority of optical phenomena, and even to learn about phenomena never before commented on”, explains physicist Vanderlei Bagnato, from the Optics and Photonics Research Center, from the São Carlos Physics Institute of the University of São Paulo (USP).

Newton had already published, in 1687, a fundamental work for mathematics, Mathematical principals of natural philosophy , known by its first name in Latin, Principia , full of formulas and geometric figures. Optics follows a different path: it was published first in English, instead of Latin, the educated language of the time, and the major part of the figures that appear are descriptions of experiments and observations. Newton deals mainly with the phenomena of the reflection and refraction of light, with the decomposition of white light into the spectrum when passing through a prism, with the colors of natural bodies, with the rainbow, with the reflecting telescope, with the colors produced by transparent and thin and thick bodies, and with the diffraction of light, amongst other studies.

The basis of Newton’s theory was the corpuscular nature of light. “Being the founder of modern mechanics, it was natural that he should try to understand the phenomena of light by means of the laws of mechanics, which deals with corpuscles of mass”, says Bagnato. This idea hit head-on the theory of another physicist and mathematician, Dutchman Christiaan Huygens (1629-1695), for whom light was propagated in waves. Neither of the theories proved totally correct, although Huygens seems to have arrived closer to the truth. The polemics never pleased Newton. When he published his first article about light and colors, in 1672, there was intense controversy in scientific circles, in which took part, besides Huygens, the astronomer John Flamsteed (1646-1719) and, chiefly, the physicist Robert Hooke (1635-1703).

“This reaction led Newton to close himself up, and in later works he rarely went back to exposing himself in such an open and frank way as in this first article”, says physicist André Koch Torres Assis, from the State University of Campinas (Unicamp), who translated Optics (Edusp, 294 pages) into Portuguese. The book was published 32 years after the polemics, one year after the death of Hooke, his main critic.

Newton was then 62 years old, although the theories had been created by him when he was 23 years old. “This book continues to be as important today as it was when it was published”, Assis believes. The central issue is the study of light, but there are considerations on metabolism and physiology, on how to carry out experiments, on philosophy, on vacuum and ether, and on vision and the senses, amongst other themes. “Optics ought even to be used as a starting point for an analysis and reflection about interdisciplinarity in the teaching of physics”, Assis suggest. “The book is reaching its 300th anniversary as solid as when it was conceived”, agrees Bagnato.

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