A kaleidoscope is a tube of mirrors containing loose colored beads, pebbles or other small colored objects. The viewer looks in one end and light enters the other end, reflecting off the mirrors. Typically there are two rectangular lengthwise mirrors. Setting of the mirrors at 45 degree (angle) creates eight duplicate images of the objects, six at 60°, and four at 90°. As the tube is rotated, the tumbling of the colored objects presents the viewer with varying colors and patterns. Any arbitrary pattern of objects shows up as a beautiful symmetric pattern because of the reflections in the mirrors. A two-mirror model yields a pattern or patterns isolated against a solid black background, while a three-mirror (closed triangle) model yields a pattern that fills the entire field.
For a 2D symmetry group, a kaleidoscopic point is a point of intersection of two or more lines of reflection symmetry. In the case of a discrete group the angle between consecutive lines is 180°/n for an integer n≥2. At this point there are n lines of reflection symmetry, and the point is a center of n-fold rotational symmetry. Modern kaleidoscopes are made of brass tubes, stained glass, wood, steel, gourds and most any other material an artist can sculpt or manipulate. The part of the kaleidoscope which holds objects to be viewed is called an object chamber or cell. Object cells may contain almost any material. Sometimes the object cell is filled with liquid so the items float and move through the object cell with slight movement from the person viewing.
First attested 1817 in English, the word "kaleidoscope" derives from the Greek καλός (kalos), "beautiful", είδος (eidos), "shape"  + σκοπέω (scopeο), "to look at, to examine"  Online Etymology Dictionary.
Known to the ancient Greeks, it was reinvented by Sir David Brewster in 1816 while conducting experiments on light polarization; Brewster patented it in 1817. His initial design was a tube with pairs of mirrors at one end, and pairs of translucent disks at the other, and beads between the two. Initially intended as a science tool, the kaleidoscope was quickly copied as a toy. Brewster believed he would make money from his popular invention; however, a fault in the wording of his patent allowed others to copy his invention.
In America, Charles Bush popularized the kaleidoscope. Today, these early products often sell for over $1,000. Cozy Baker collected kaleidoscopes and wrote books about a few of the artists who were making them in the 1970s through 2000. Baker is credited with energizing a renaissance in kaleidoscope-making in America. In 1999 a short lived magazine dedicated to kaleidoscopes called Kaleidoscope Review was published covering artists, collectors, dealers, events, and 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.
Craft galleries often carry a few, while others specialize in them and carry dozens of different types from different artists and craftspeople.
- Fractals (Kaleidoscopes are related to hyperbolic geometry)
- Kalos, Henry George Liddell, Robert Scott, "A Greek-English Lexicon", at Perseus
- Eidos, Henry George Liddell, Robert Scott, "A Greek-English Lexicon", at Perseus
- Skopeo, Henry George Liddell, Robert Scott, "A Greek-English Lexicon", at Perseus
- Online Etymology Dictionary