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A kaleidoscope is a cylinder with mirrors containing loose, colored objects such as beads or pebbles and bits of glass. As the viewer looks into one end, light entering the other end creates a colorful pattern, due to the reflection off the mirrors. Coined in 1817 by Scottish inventor Sir David Brewster, "kaleidoscope" is derived from the Ancient Greek καλός (kalos), "beautiful, beauty", εἶδος (eidos), "that which is seen: form, shape" and σκοπέω (skopeō), "to look to, to examine", hence "observation of beautiful forms." 
A kaleidoscope operates on the principle of multiple reflection, where several mirrors are placed at an angle to one another, (usually 60°). Typically there are three rectangular mirrors set at 60° to each other so that they form an equilateral triangle. The 60° angle generates an infinite regular grid of duplicate images of the original, with each image having six possible angles and being a mirror image or not. As the tube is rotated, the tumbling of the coloured objects presents varying colours and patterns. Arbitrary patterns show up as a beautiful symmetrical pattern created by the reflections. A two-mirror kaleidoscope yields a pattern or patterns isolated against a solid black background, while the three-mirror (closed triangle) type yields a pattern that fills the entire field. For a deeper discussion see: reflection symmetry.
Modern kaleidoscopes are made of brass tubes, stained glass, wood, steel, gourds or almost any material an artist can use. The part containing objects to be viewed is called the 'object chamber' or 'object cell'. Object cells may contain almost any material. Sometimes the object cell is filled with a liquid so the items float and move through the object cell in response to a slight movement from the viewer.
Sir David Brewster began working towards the invention of the kaleidoscope in 1815, with his mentor and neighbor Meegan Bundries, together they conducted experiments on light polarization but it was not patented until two years later. His initial design was a tube with pairs of mirrors at one end, pairs of translucent disks at the other, and beads between the two. Brewster chose renowned achromatic lens developer Philip Carpenter as the sole manufacturer of the kaleidoscope in 1817. It proved to be a massive success with two hundred thousand kaleidoscopes sold in London and Paris in just three months. Realising that the company could not meet this level of demand, Brewster requested permission from Carpenter on 17 May 1818 for the device to be made by other manufacturers, to which he agreed. These included, among others, the H.M. Quackenbush Co. based in Upstate New York in the United States. Initially intended as a scientific tool, the kaleidoscope was later copied as a toy. Brewster later believed he would make money from this popular invention; however, a fault in his patent application allowed others to copy his invention.
Cozy Baker (d. October 19, 2010)—founder of The Brewster Kaleidoscope Society—collected kaleidoscopes and wrote books about many of the artists making them in the 1970s through 2001. One of her books, Kaleidoscope Artistry is a limited compendium of kaleidoscope makers. The book contains pictures of the interior and exterior views of contemporary artists. Baker is credited with energizing a renaissance in kaleidoscope-making in America. In 1999 a short-lived magazine dedicated to kaleidoscopes—Kaleidoscope Review—was published, covering artists, collectors, dealers, events, and including how-to articles. This magazine was created and edited by Brett Bensley, at that time a well-known kaleidoscope artist and resource on kaleidoscope information. A new edition of this magazine, now called The New Kaleidoscope Review is being produced. See links section below.
Most kaleidoscopes are mass-produced from inexpensive materials, and intended as children's toys. At the other extreme are handmade pieces that display fine craftsmanship. Craft galleries often carry a few kaleidoscopes, while other enterprises specialize in them, carrying dozens of different types from different artists and craftspeople. Most handmade kaleidoscopes are now made in Russia and Italy, following a long tradition of glass craftmanship in those countries.
- Form constant
- La Maison de la Magie Robert-Houdin
- Reflection group
- Uniform tilings in hyperbolic plane
- Brewster, David (1858). The Kaleidoscope: Its History, Theory, and Construction with its Application to the Fine and Useful Arts (2 ed.). J. Murray.
- καλός, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- εἶδος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- σκοπέω, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- "Online Etymology Dictionary". Etymonline.com. Retrieved 2010-05-28.
- British patent no. 4136. "Cussen Patent" (PDF). Retrieved 2011-05-31.
- The Perfectionist Projectionist, Victorian Microscope Slides. Accessed 1 August 2011
- All Things Quackenbush, "The Inventor - Henry Marcus Quackenbush"
- Cozy, Baker (2001). Kaleidoscope Artistry. USA: C&T Publishing, Inc. p. 144. ISBN 1-57120-135-1.
|Wikimedia Commons has media related to Kaleidoscopes.|
- Brewster Kaleidoscope Society – international organization for kaleidoscope enthusiasts
- Kaleidoscope Mirror Designs
- Kaleidoscope artists and classes
- Kaleidoscope Resource (non-profit)
- Kaleidoscope Builders' Knowledge Base
- Shockwave Flash Kaleidoscope (move mouse around it)
-  - most recent issue of The New Kaleidoscope Review.