Newton disc

The Newton disc, also known as the Disappearing Colour Disc, is a well-known physics experiment with a rotating disc with segments in different colors (usually Newton's primary colors: red, orange, yellow, green, blue, indigo, and violet or ROYGBIV) appearing as white (or off-white or gray) when it spins very fast.

Color distribution of a Newton disc.

This type of mix of light stimuli is called temporal optical mixing, a version of additive-averaging mixing.[1] The concept that human visual perception cannot distinguish details of high-speed movements is popularly known as persistence of vision.

The disc is named after Isaac Newton. Although he published a circular diagram with segments for the primary colors that he had discovered, it is uncertain whether he actually ever used a spinning disc to demonstrate the principles of light.

Transparent variations for magic lantern projection have been produced.[2]

History

Around 165 CE, Ptolemy described in his book Optics a rotating potter's wheel with different colors on it. He noted how the different colors of sectors mixed together into one color and how dots appeared as circles when the wheel was spinning very fast. When lines are drawn across the axis of the disc they make the whole surface appear to be of a uniform color. "The visual impression that is created in the first revolution is invariably followed by repeated instances that subsequently produce an identical impression. This also happens in the case of shooting stars, whose light seems distended on account of their speed of motion, all according to the amount of perceptible distance it passes along with the sensible impression that arises in the visual faculty."[3][4]

Porphyry (c. 243 – c. 305) wrote in his commentary on Ptolemy's Harmonics how the senses are not stable but confused and inaccurate. Certain intervals between repeated impressions are not detected. A white or black spot on a spinning cone (or top) appears as a circle of that color and a line on the top makes the whole surface appear in that color. "Because of the swiftness of the movement we receive the impression of the line on every part of the cone as the line moves."[5] in the 11th century Ibn al-Haytam, who was familiar with Ptolemy's writings, described how colored lines on a spinning top could not be discerned as different colors but appeared as one new color composed of all of the colors of the lines. He deducted that sight needs some time to discern a color. al-Haytam also noted that the top appeared motionless when spun extremely quick "for none of its points remains fixed in the same spot for any perceptible time".[6]

Newton's primary colours

On 6 February 1671, Isaac Newton wrote a paper about the experiments he had been conducting since 1666 with the refraction of light through glass prisms. He concluded that the different refracted rays of light – well parted from others – could not be changed by further refraction, nor by reflection or other means, except through mixture with other rays. He thus found the seven primary colors red, orange, yellow, green, blue, "a violet-purple" and indigo. When mixing the coloured rays from a prism, he found that "the most surprising and wonderful composition was that of whiteness" requiring all the primary colors "mixed in a due proportion".[7]

In reaction to Robert Hooke's criticism of the new theory of light, Newton published a letter in the Philosophical Transactions in 17, with other experiments that proved how sunlight existed of rays with different colours. He described how the cogs or teeth of a gyrating wheel behind a prism can block part of the light so that all the colours would be projected successively if the wheel turns rather slow, but how all the colours will be mixed into white light if the wheel turn very fast. He also pointed out that rays of light that were reflected from multi-coloured bodies were weakened by the loss of many rays and that a mixture of those rays would not produce a pure white, but a gray or "dirty" colour. This could be seen in dust, which on close inspection would reveal that it consists of many coloured particles, or when mixing several colours of paint. He also referred to a child's top which would display a "dirty" colour if it was painted in several colours and made to spin fast by whipping it.[8]

After presenting his conclusions about dividing sunlight into primary colors and mixing them back together into white light, Newton presented a color circle to illustrate the relations between these colors in his book Opticks (1704).[9]

Many modern sources state that Isaac Newton himself used a spinning disc with colored sectors to demonstrate how white light was actually the compound of the primary colors.[10][11][12] However, these do not reference any historical source.

According to Joseph Plateau the first to describe how a spinning disc with Newton's seven primary colours would show an (imperfect) white colour was Pieter van Musschenbroek in 1762.[13]

See also

References
  1. Briggs, David (2012-08-12). "Additive mixing, additive-averaging". The Dimensions of Colour. Retrieved 2018-08-11.
  2. Greenslade, Jr., Thomas B. "Newton's Color Wheel". Instruments for Natural Philosophy. Kenyon College. Retrieved 2018-08-11.
  3. Smith, A. Mark (1999). Ptolemy and the Foundations of Ancient Mathematical Optics: A Source Based Guided Study. American Philosophical Society. ISBN 9780871698933.
  4. Smith, A. Mark (1996). "Ptolemy's Theory of Visual Perception: An English Translation of the "Optics" with Introduction and Commentary". Transactions of the American Philosophical Society. 86 (2): iii–300. doi:10.2307/3231951. JSTOR 3231951.
  5. Barker, Andrew (2015-09-15). Porphyry's Commentary on Ptolemy's Harmonics: A Greek Text and Annotated Translation. Cambridge University Press. ISBN 9781107003859.
  6. Alhazen (2001). Smith, A. Mark (ed.). Alhacen's Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen's De Aspectibus, the Medieval Latin Version of Ibn Al-Haytham's Kitab Al-Manazir. American Philosophical Society. ISBN 9780871699145.
  7. Newton, Isaac (1671). "A Letter of Mr. Isaac Newton, Professor of the Mathematicks in the University of Cambridge; Containing His New Theory about Light and Colors: Sent by the Author to the Publisher from Cambridge, Febr. 6. 1671/72; In Order to be Communicated to the R. Society". Philosophical Transactions of the Royal Society. 6 (80): 3075–3087. Bibcode:1671RSPT....6.3075N. doi:10.1098/rstl.1671.0072. JSTOR 101125.
  8. Royal Society (Great Britain); Britain), Royal Society (Great; Hutton, Charles; Maty, Paul Henry; Pearson, Richard; Shaw, George; Stuart, Alexander; Britain), Royal Society (Great; Britain), Royal Society (Great (1672). Philosophical transactions of the Royal Society of London. v.7-8=no.81-100 (1672-1673). London: Royal Society of London.
  9. Newton, Isaac (1730). Opticks: Or, A Treatise of the Reflections, Refractions, Inflections and Colours of Light. William Innys at the West-End of St. Paul's. pp. 154–158.
  10. Weinhold, Adolf Ferdinand; Loewy, Benjamin (1875). Introduction to Experimental Physics, Theoretical and Practical: Including Directions for Constructing Physical Apparatus and for Making Experiments. Longmans, Green. p. 541.
  11. Isaac Newton.
  12. Pereira, David (2011-06-30). The Art of HDR Photography. ISBN 9781937367022.
  13. Mémoires de l'Academie royale des sciences, des lettres et des beaux-arts de Belgique (in French). L'Académie. 1878.
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