Newton’s Optics established a new theory of light and a more quantitative and experimental style of science. Also, the term “light” provided the central metaphor for the intellectual age called the Enlightenment.

Sir Isaac Newton once famously said that if he saw farther than others, it was because he “stood on the shoulders of giants.” As a student at Cambridge University from 1661 to 1665, he studied carefully the work of Johannes Kepler, René Descartes, and other giants of the Scientific Revolution. Scientific Revolution This led him to a series of optical experiments and a 1672 paper on a new theory of color delivered to the Royal Society of London. A long series of disputes followed, culminating with the publication of Newton’s Opticks (1704; better known as Optics) by the Royal Society of London. [kw]Newton Publishes Optics (1704)
[kw]Optics, Newton Publishes (1704)
[kw]Publishes Optics, Newton (1704)
Optics (Newton)
Light;theory of
Science;experimental
[g]England;1704: Newton Publishes Optics[0170]
[c]Physics;1704: Newton Publishes Optics[0170]
[c]Science and technology;1704: Newton Publishes Optics[0170]
[c]Astronomy;1704: Newton Publishes Optics[0170]
[c]Mathematics;1704: Newton Publishes Optics[0170]
Newton, Sir Isaac;Optics
Kepler, Johannes
Descartes, René
Hooke, Robert
Huygens, Christiaan

At Cambridge, Newton was introduced to optics by reading Kepler’s Dioptrice
Dioptrice (Kepler) (1611; ray optics), which initiated the modern study of optics. Newton also read Descartes’s Dioptrique
Dioptrique (Descartes) (1637; ray optics), which offered a mechanical theory of light as an instantaneous transmission of pressure transmitted by a luminous medium made up of moving particles. Descartes had claimed that the bending of light in refraction was caused by an increase in the speed of particles as they pass into a denser medium. He proposed that the colors produced in refraction were caused by particle rotations, faster for red and slower for blue. Thus, color was a modification of the pure homogeneous white light coming from these rotations. Newton’s teacher at Cambridge, Isaac Barrow, Barrow, Isaac gave lectures on optics in 1664, which also suggested that colors result from modifications of white light.

Newton became interested in colors Color theory caused by refraction in lenses when he used lenses to construct a telescope, producing images surrounded by colored fringes. He then obtained a prism to study how colors are formed from white light by refraction. He passed sunlight from a small hole in the window shades through his prism and refracted it to the opposite wall. When he saw that the resulting spectrum was much longer than its breadth, he began to develop the idea that white light is not homogeneous, but is a mixture of colors, and that the elongation of the spectrum comes from different colors refracting at different angles. In later years, Newton claimed that his theory of colors, along with his formulation of the calculus and the law of universal gravitation, were all conceived during the plague years of 1665 and 1666, when students were sent home from school for nearly two years.

After returning to Cambridge as a fellow, Newton constructed the first reflecting telescope, Telescopes in 1668, to avoid the problem of image distortion due to refraction. The telescope was only six inches long, but it magnified forty times by focusing light with a concave mirror instead of a lens. An urgent request soon came from the Royal Society to examine the telescope, so Newton constructed an improved nine-inch version and sent it to London; the response was enthusiastic. The Royal Society asked for a written account of his invention, leading to Newton’s reply, his first scientific paper, “New Theory About Light and Colours,” “New Theory About Light and Colours” (Newton)[New Theory About Light and Colours] published in the Philosophical Transactions of the Royal Society in March of 1672. Although this paper led to his election as a fellow of the Royal Society, it also gave rise to an extended controversy, including ten critical letters from half a dozen authors in the Philosophical Transactions and eleven replies by Newton. Robert Hooke led the opposition, which rejected the heterogeneous nature of light and preferred various forms of the wave theory that had been developed by Christiaan Huygens.

Diagrams of optical phenomena created by Sir Isaac Newton to illustrate the first edition of his Opticks. The phenomena pictured include a rainbow and the refraction of light through Icelandic spar (a type of crystal) and through a prism.

(Library of Congress)

Soon Newton became impatient with the philosophical and hypothetical arguments of his critics and insisted that science should be primarily mathematical and experimental. After about four years, he “retreated” to doing research and teaching for about a decade. In 1684 he was finally persuaded by astronomer Edmond Halley to publish his laws of motion and universal gravitation, resulting in the masterpiece Philosophiae naturalis principia mathematica (1687; The Mathematical Principles of Natural Philosophy, Mathematical Principles of Natural Philosophy, The (Newton) 1729; best known as the Principia, 1848), which resolved the most difficult problems of the Scientific Revolution and established Newton’s reputation.

After Hooke died in 1703, Newton was elected president of the Royal Society. A year later he published Optics, written in English for a more receptive audience, which now recognized the value of his experimental and mathematical arguments. Optics described his many experiments on light. His separation of white light with a prism associated quantitative angles of refraction with each of the colors, which he rather arbitrarily designated as seven: red, orange, yellow, green, blue, indigo, and violet. He gave the first complete account of the rainbow and explained the color of a given object as the combination of colors it reflects after absorbing all others.

While the Principia had proved Newton a brilliant mathematician, the easier-to-read Optics revealed his skill as an experimenter. In book 1 of three books in the Optics, he describes his experiments with the spectrum. Spectra A crucial experiment demonstrated that each color is a pure component of white light by passing a single color in the spectrum through a hole and showing that a second prism refracted it the same amount without changing its color. Another experiment passed the dispersed rays of the spectrum from one prism through an inverted second prism that recombined these rays to form white light again.

In book 2 Newton examines the colored rings formed when a lens is pressed against a flat pane of glass, first studied by Hooke but called “Newton rings.” Careful measurements showed that the gap between the lens and the glass increases uniformly with each ring so that the “interval of the fits” is related to the colors. Theorizing these “fits” was as close as he could get to a determination of the wavelength of light, but he avoided any such hypothesis.

In book 3 Newton discusses the 1665 experiments of astronomer Francesco Maria Grimaldi, which produced colored fringes when white light passed through two successive slits (diffraction). Newton attempts to explain this result in terms of attractive forces rather than waves. His preference for the particle theory of light led him to conclude that light travels faster when it passes into denser media. However, the more hypothetical issues about the nature of light were mostly relegated to the sixteen “queries” at the end of the 1704 edition of the Optics.

Sir Isaac Newton’s Optics established a more experimental and quantitative style in science for the eighteenth century, which contrasted with the earlier, more speculative, hypothetical approach. However, in the 1706 Latin edition of Optics, he added new queries that suggested the particle theory of light, Particle theory of light and in the 1717 and 1730 English editions he expanded on these queries. Newton’s particle theory influenced other scientists, delaying the acceptance of the wave theory for nearly a century. In the nineteenth century the wavelengths of visible light were finally measured, and light was shown to slow down in denser media, as predicted by the wave theory. Newton’s early ambivalence between particle and wave theories is reflected in modern quantum theory, which attributes both particle and wave properties to light.

The careful reasoning and experimental approach of the Optics became a paradigm for the eighteenth century Enlightenment, Enlightenment;definition of including its central metaphor of light. Newton’s work was widely celebrated in literature and poetry, and he was considered a prophet for future progress. The laws of nature, both of motion and of light, soon came to be seen as a reflection of order and beauty, and the spectrum became a new symbol for the descriptive poet. Where the Principia had been viewed as cold philosophy, the Optics opened up the literary imagination to light and color, making itself felt in the works of poets over the next generations.

• Andrade, E. N. da C. Sir Isaac Newton: His Life and Work. New York: Macmillan, 1954. A readable account of Newton’s life, with a chapter on the Optics.
• Cohen, I. Bernard, and George E. Smith, eds. The Cambridge Companion to Newton. New York: Cambridge University Press, 2002. This compilation on Newton’s work includes the chapter “Newton’s Optics and Atomism” by Alan Shapiro.
• Newton, Isaac. Opticks: Or, A Treatise of the Reflexions, Refractions, Inflexions, and Colours of Light. New York: Dover, 1952. This reprint of the 1730 edition of the Optics includes a foreword by Albert Einstein, a good historical introduction by Edmund Whittaker, a preface by Bernard Cohen, and an analytical table of contents by Duane H. D. Roller.
• Nicolson, Marjorie Hope. Newton Demands the Muse: Newton’s “Opticks” and the Eighteenth Century Poets. London: Archon Books, 1963. This classic book describes the influence of Newton and the Optics on the eighteenth century literary imagination.
• Rossi, Paoli. The Birth of Modern Science. Translated by Cynthia De Nardi Ipsen. Malden, Mass.: Blackwell, 2001. This translation from the original Italian work includes a good discussion of Newton’s optics in chapter 17.

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Light;theory of
Science;experimental