Editing Persistence of vision (section)

==Natural occurrences and applications==
Impressions of several natural phenomena and the principles of some optical toys have been attributed to persistence of vision. In 1768, [[Patrick D'Arcy]] recognised the effect in "the luminous ring that we see by turning a torch quickly, the fire wheels in the fireworks, the flattened spindle shape we see in a vibrating cord, the continuous circle we see in a cogwheel that turns with speed".<ref name=d'Arcy1768 /> Basically everything that resembles motion blur seen in fast moving objects could be regarded as "persistence of vision".

===Sparkler's trail effect===
The apparent line of light behind a fast moving luminous object is known as the "sparkler's trail effect", since it is commonly known from the use of [[sparkler]]s.

===Light painting===
{{Main|Light painting}}
[[File:Light painting screw.jpg|''Light Painting Screw'' by Karsten Knöfler|thumb]]
The effect has occasionally been applied in the arts by writing or drawing with a light source recorded by a camera with a long exposure time.

This concept has been further developed into media with computer-controlled moving light sources (nowadays mostly [[LED light]]), known as S.W.I.M. (Sequential Wave Imprinting Machine). However, like video and television, the technology actually gets rid of the visual trail of fast-moving lights by presenting a stroboscopic sequence of very short visual cues (resulting in a sharp image, still or animated).

===Color-top / Newton disc===
{{Main|Newton disc}}
Colors on spinning tops or rotating wheels mix together if the motion is too fast to register the details. A colored dot then appears as a circle and one line can make the whole surface appear in one uniform hue.

The Newton disc optically mixes wedges of [[Isaac Newton]]'s primary colors into one (off-)white surface when it spins fast.

===Thaumatrope===
In April 1825 the first ''[[Thaumatrope]]'' was published by W. Phillips (in anonymous association with [[John Ayrton Paris]]).<ref name="Herbert">{{cite web |url=http://www.stephenherbert.co.uk/thaumatropeTEXT1.htm |last=Herbert |first=Stephen |title=Wheel of Life - The Taumatrope |access-date=2017-02-26 |archive-date=2014-05-05 |archive-url=https://web.archive.org/web/20140505163311/http://www.stephenherbert.co.uk/thaumatropeTEXT1.htm |url-status=usurped }}</ref> The fact that the pictures on either side of the twirling disc seem to blend together into one image has often falsely been presented as an illustration of the effect of persistence of vision (the fusion instead depends on stroboscopic interruptions and the compatibility of the mental impressions of the two alternating pictures).

The differences between impressions of quick alternations of two figures –depending on [[tachistoscope]] frequencies, distance between the figures, and/or variance in shapes– was studied by [[Max Wertheimer]] in 1912.<ref name=Wertheimer/> These experiments inspired the theories of [[Gestalt psychology]].

===Kaleidoscopic colour-top===
In April 1858 John Gorham patented his ''Kaleidoscopic colour-top''.<ref>[http://www.fleaglass.com/ads/gorham-patent-kaleidoscopic-top/]{{dead link|date=April 2020}}</ref> This is a [[Spinning top|top]] on which two small discs are placed, usually one with colors and a black one with cut-out patterns. When the discs spin and the top disc is retarded into regular jerky motions the toy exhibits "beautiful forms which are similar to those of the [[kaleidoscope]]" with multiplied colours. Gorham described how the colours appear mixed on the spinning top "from the duration of successive impressions on the retina". Gorham founded the principle on "the well-known experiment of whirling a stick, ignited at one end" (a.k.a. the sparkler's trail effect).<ref>{{cite book|url=https://books.google.com/books?id=ZrdbAAAAcAAJ|last=Gorham|first=John|title=The Rotation of Coloured Discs|date=January 1859}}</ref>

===Rubber pencil trick===
A pencil or another rigid straight line can appear as bending like flexible rubber when it is wiggled fast enough between fingers, or otherwise undergoing rigid motion.

Persistence of vision has been discarded as sole cause of the illusion. It is thought that the eye movements of the observer fail to track the motions of features of the object.<ref>{{cite journal|title=Illusory bending of a rigidly moving line segment: Effects of image motion and smooth pursuit eye movements|first1=Lore|last1=Thaler|first2=James T.|last2=Todd|first3=Miriam|last3=Spering|first4=Karl R.|last4=Gegenfurtner|date=1 April 2007|journal=Journal of Vision|volume=7|issue=6|page=9|doi=10.1167/7.6.9|pmid = 17685792|doi-access=free}}</ref>

This effect is widely known as an entertaining "magic" trick for children.<ref>{{cite web|url=https://www.thespruce.com/rubber-pencil-kids-magic-tricks-2267012|title=Easy Magic Tricks for Kids: The Rubber Pencil|website=TheSpruce.com|access-date=29 October 2017}}</ref>