Turn a kaleidoscope and the picture inside changes with every twist. What is going on in that small tube, and who thought of it? Here is the short story, with sources.
The short version
- A kaleidoscope has two or more mirrors tilted to each other at an angle, so a few small objects are shown as a symmetrical pattern.
- The coloured glass sits loose in a cell at one end. Turning the cell moves the pieces, so the view keeps changing.
- It was invented by the Scottish scientist David Brewster, about 1815, and patented in 1817.
The short answer
A kaleidoscope is a tube with “two or more reflecting surfaces (or mirrors) tilted to each other at an angle.” One or more objects at one end of the mirrors are shown as a symmetrical pattern when you look in from the other end.
The mirrors do the work. A mirror gives what is called specular reflection, the “mirror-like reflection of waves, such as light, from a surface,” and the law of reflection says that the angle of reflection of a ray equals the angle of incidence. With the mirrors set at an angle, the light is reflected between them again and again, and that repeated reflection produces the symmetrical images. That is why a handful of glass pieces turns into a repeating picture.
What is inside
There are only two ideas in the tube:
- The mirrors. Two or more, tilted to each other.
- The cell. It is “usually containing on one end a cell with loose, colored pieces of glass or other transparent” objects. “Rotation of the cell causes motion of the materials, resulting in an ever-changing view being presented.”
Why the angle matters
The angle between the mirrors decides the pattern. David Brewster, the inventor, tried several. Here is what the sources say he described:
| Mirror set-up | What Brewster wrote about it |
|---|---|
| 18°, 20° or 22½° | In his patent he deemed these “most pleasing.” |
| 45°, 36° and 30° | These are the primary examples in his treatise. |
| 60° (equilateral triangle) | An infinite pattern of equilateral triangles, deemed “uncommonly splendid” by Brewster. |
| 90°, 60° and 30° | A pattern with 31 reflected images of the aperture, not symmetrically arranged around the centre. |
| Four reflectors | A square or rectangular kaleidoscope with an infinite pattern of squares or rectangles. |
So a different angle is not a small detail. It changes what the pattern looks like.
Who invented the kaleidoscope?
The Scottish scientist Sir David Brewster (11 December 1781 – 10 February 1868), “a British scientist, inventor, author, and academic administrator,” “principally remembered for his experimental work in physical optics.” His invention of the kaleidoscope dates to “about 1815,” and British patent no. 4136 “was granted in July 1817.”
Brewster also gave it its name. “The term ‘kaleidoscope’ was coined by its Scottish inventor David Brewster.” It comes from three Ancient Greek words, kalos (“beautiful, beauty”), eidos (“form, appearance”) and skopeo (“to look, to examine”), “hence ‘observation of beautiful forms’.”
A hit that did not make its inventor rich
Sales were fast: an estimated two hundred thousand kaleidoscopes were sold in London and Paris in just three months. But “a copy of the prototype was shown to London opticians and copied before the patent was granted,” and the patent “yielded no direct financial benefits to Brewster.”
You can still see early ones. The Science Museum Group in the UK holds Brewster’s Patent Kaleidoscope by Philip Carpenter, Birmingham, England, 1820, made of silver-plated brass, “with extra lens for distant objects, and 13 various object plates.” Wikipedia adds that Carpenter’s company “would keep on selling kaleidoscopes for 60 years.”
Is a kaleidoscope a toy for kids?
It is a very old, very simple kind of play: look in, turn, look again. The sources above do not set an age for it, so we will not make one up. A kaleidoscope usually has a cell with loose pieces of coloured glass, so it is worth checking the age and safety notes of each one before you give it to a young child.
What we would pick
If you want to try one, we like a kaleidoscope you look at as much as through. Our Van Gogh Kaleidoscope has a Van Gogh painting printed on a slim metal barrel with golden-toned rings, and a window of coloured glass chips at the top end catches the light. You choose one of six paintings, such as Starry Night over the Rhône or Wheatfield with Crows, and a pattern with nine petals or ten. It comes in a gift box, with no batteries and no screens.
One honest note: we do not have a confirmed age range or glass-safety details for this model, so we do not state one here. If you are buying it for a young child, ask us first.
Sources
- Kaleidoscope, Wikipedia: the mirrors tilted at an angle and the symmetrical pattern, the cell with loose coloured glass, Brewster’s angles, the name from Greek, patent GB 4136 granted in July 1817, 200,000 sold in three months, Carpenter’s company selling for 60 years.
- David Brewster, Wikipedia: his dates and work in optics, the invention of the kaleidoscope in about 1815, the 1817 patent, early copying and no direct financial benefit.
- Specular reflection, Wikipedia: mirror-like reflection and the law of reflection.
- Brewster’s Patent Kaleidoscope by Philip Carpenter, Birmingham, England, 1820, Science Museum Group collection: the object, its extra lens and 13 object plates.
