Miniature Kaleidoscopes: The One-Inch Instruments Used as Ornaments in 1819

3 days ago

8 min read

By Rocco (Roi) Ramon - licensed architect, founder of Studio Yabaye

Kaleidoscope pendants and necklace-size instruments are usually presented as a recent product type. The written record is older. Two years after the kaleidoscope became public, its inventor described instruments one inch long and stated that they were already in use as a personal ornament.

The source is Sir David Brewster's "A Treatise on the Kaleidoscope" (Edinburgh, 1819), Chapter XIV, "On the Construction of Microscopic Kaleidoscopes". The chapter is short - it runs from page 108 to page 110 - and most of it is a construction specification. This article reports what the chapter says, states what it does not say, and explains why a small kaleidoscope is harder to build than a large one. Chapter numbers below are those of the 1819 edition; the 1858 edition is numbered differently, and there the microscopic kaleidoscope is Chapter XVIII.

What Brewster means by a microscopic kaleidoscope

Brewster gives the name to two different instruments:

A kaleidoscope for microscopic objects. The instrument forms its symmetrical pattern from objects that are themselves very small.
A kaleidoscope that is itself very short. The reflectors are so short that a lens of high power is needed at one end in order to see, and magnify, the objects at the other end.

The second form is the miniature instrument. Brewster states its size from his own bench work: he had often constructed both forms "so small as one inch and one inch and a half in length". Converted, that is 25.4 mm to 38.1 mm (conversion: 1 inch = 25.4 mm).

The chapter gives length only. It gives no tube diameter and no reflector width.

What the text says about wearing them

The whole of the evidence is one clause. Brewster writes that the kaleidoscope in this minute state had been applied, both in Britain and abroad, as "a female ornament", and that he would therefore set out the best method of constructing it.

That clause supports three statements:

Instruments of this size existed in more than one country by 1819.
They were used as an ornament for women.
Brewster gives that use as his reason for setting out the method of construction.

It does not support more than that. The chapter does not say whether the instrument was hung on a chain, set in a ring, fitted to a seal or pinned to clothing. It names no maker, no jeweller, no city and no case material. It gives no quantity. Any description of a kaleidoscope necklace, ring or brooch of that period needs a different source.

For the wider demand of those years, see the kaleidoscope craze. For the invention itself, see the history of the kaleidoscope.

Why a short kaleidoscope is harder to build

Brewster opens the technical part with two penalties of short reflectors. The aberration from symmetry increases as the length of the reflectors is reduced, and the light of the field diminishes from the same cause. His conclusion is that it becomes "extremely difficult to obtain correct figures" and uniform light in small instruments.

A third penalty follows a few lines later. The aberration also increases with the distance of the object from the ends of the reflectors, and Brewster notes that this effect is much augmented in small instruments.

Chapter XIII of the same edition, on projection instruments, supplies a scaling rule. Brewster takes an example: if reflectors five inches long (127 mm, conversion) allow an eye-end aperture of one-fourth of an inch (6.4 mm, conversion), then plates ten inches long allow two-fourths of an inch, with symmetry and brightness unchanged. The usable aperture is proportional to the length. In his example the ratio is 1 to 20.

Applied to a miniature, the example ratio gives the following. This is my arithmetic from Brewster's example, not a figure he states for the miniature:

1.5 inch reflectors: aperture about 0.075 inch, or 1.9 mm.
1 inch reflectors: aperture about 0.05 inch, or 1.3 mm.

The consequence for accuracy is direct. An error in the mirror angle, a chip on the junction edge or a gap under the object has a fixed physical size. In a long instrument it is a small fraction of the aperture. In a one-inch instrument the same error is a large fraction of an aperture under 2 mm. This explanation is mine; Brewster states only that the aberration grows as the reflectors shorten.

Brewster's specification for the miniature

Chapter XIV then lists the measures that keep the errors as small as possible.

Reflectors. They should be metallic: polished steel or polished speculum metal. A polished metal reflects from its front surface. In Chapters II and III Brewster explains that a glass plate reflects from its posterior surface as well as its first surface, which gives a second set of images. My notes on front-surface mirrors cover the present-day equivalent.

Angle. The inclination of the reflectors should not be less than 36 or 45 degrees. These give 10 and 8 sectors. Brewster gives no reason here. A smaller angle means more reflections and narrower sectors in a field that is already dim. The arithmetic is in kaleidoscope mirror angles.

Eye-hole. It should not exceed 1/15 of an inch in diameter - 1.7 mm (conversion) - and must sit as near as possible to the angular point of the reflectors.

Three and four mirrors. The same directions apply. The reflectors must taper nearly to a point at the eye end, leaving an aperture no greater than the same 1/15 of an inch.

Solid glass. Miniatures can also be made of solid glass, working by internal reflection. For these Brewster refers the reader to an earlier chapter for the focal length of the lens.

The objects and the mica window

The chapter does not list specific objects for the miniature. It gives three requirements instead:

Thin and slender. The objects should be as thin as they can be made, so that they lie as close as possible to the reflector ends.
Brilliant colour. Brewster asks for colours that are brilliant and not gloomy. The field is dim, so saturated, transparent colours are needed.
Minimum distance. The objects must be at the least possible distance from the reflectors.

The separating window is specified as a thin film of the most transparent mica, not glass. Brewster's reason is mechanical: mica is tough and elastic at a thickness at which glass could hardly be obtained. He admits that mica scratches easily and answers that a scratched film is easily replaced.

He adds one refinement. The mica can be bent into a slight concavity, so that the objects lie a little inside the ends of the reflectors and not outside them.

The chapter does not state whether the objects were loose or fixed in place.

The lens at the eye end

A human eye cannot focus on an object one inch away. Chapter VI of the Treatise gives the general rule: when the reflectors are shorter than the shortest distance of distinct vision, a convex lens goes at the eye end, with a focal length equal to the length of the reflectors or an inch or two greater. He adds that the lens must be removed for short-sighted users.

Chapter XIV refines this for the miniature. The focal length must not be exactly equal to the distance of the objects from the eye. It should be as much greater as possible, so that the eye can still reach distinct vision "by a little exertion".

Brewster's reason is geometric. The sector seen directly lies at the object distance. The reflected sectors are seen along longer, folded paths, so their images are thrown further from the eye. A lens set exactly for the nearest part of the picture leaves the outer sectors out of focus. The focal length therefore has to be a mean between the distances of the different parts of the picture.

The chapter ends by noting that these instruments may also be fitted up with a draw tube and lens.

From 1819 to pendant and pocket instruments

Kaleidoscopes small enough to be worn on a chain are made today. The physical constraints have not changed. A short instrument still needs a lens if the object lies nearer than the eye can focus, still gives a dimmer field than a long one, and still shows angle and junction errors as a larger share of its aperture.

At Studio Yabaye I build brass kaleidoscopes with front-surface mirror systems in several configurations. The range includes a pocket-size brass kaleidoscope 9 cm long - a brass tube, cut, fitted and hand-finished in the studio. At 90 mm it is more than twice the length of Brewster's 38.1 mm upper figure, which places it in a different class from the instruments of Chapter XIV: hand-held, not worn. For the effect of proportions on the image, see kaleidoscope mirror length and width ratio.

What to check in a miniature kaleidoscope

These checks are my own practice, not a procedure from the Treatise.

Focus. The pattern should be sharp with a relaxed eye. If only the central wedge is sharp and the outer sectors are soft, the lens is set too short.

Sector count. Follow one shape around the centre. In a two-mirror instrument the count should be even: 8 or 10 at Brewster's recommended angles.

Centre. All sectors meet at one point. A dark or ragged centre indicates a poor junction between the reflectors.

Closing seam. In the sector opposite the open wedge, lines should continue without a step.

Brightness. Compare the outer sectors with the direct one. Kaleidoscopes need direct, preferably strong light, not side light.

Checklist

Length stated by the maker, in mm.
Lens present at the eye end if the instrument is shorter than a comfortable focusing distance.
Outer sectors as sharp as the direct sector.
Even sector count; no step at the closing seam.
Clean centre point.
No doubled edges next to reflected lines.
Colours saturated enough to read in a dim field.

Further criteria are in what to look for when buying a kaleidoscope.

FAQ

How small were kaleidoscopes made in 1819?

In Chapter XIV of "A Treatise on the Kaleidoscope" (1819), Sir David Brewster states that he had often constructed microscopic kaleidoscopes one inch and one and a half inches long. Converted, that is 25.4 mm to 38.1 mm. The chapter gives the length only, with no tube diameter.

Were kaleidoscopes worn as jewellery in the 19th century?

Brewster's 1819 Treatise records that the kaleidoscope in its minute state, 1 to 1.5 inches long, had been applied in Britain and abroad as a female ornament. The text does not say whether it was mounted as a pendant, ring or brooch, and it names no maker or jeweller.

Why does a miniature kaleidoscope need a lens?

The eye cannot focus on an object 25 to 38 mm away. Brewster's 1819 Treatise specifies a convex lens at the eye end whenever the reflectors are shorter than the nearest distance of distinct vision. For the miniature he gives no number: the focal length must be somewhat greater than the distance from the eye to the objects.

What mirrors did Brewster recommend for a small kaleidoscope?

Metallic reflectors of polished steel or polished speculum metal, set at an angle of not less than 36 or 45 degrees, which gives 10 or 8 sectors. The eye-hole should not exceed 1/15 of an inch, about 1.7 mm, and must sit as near as possible to the angular point.

Why is a miniature kaleidoscope harder to build accurately?

Brewster states that the aberration from symmetry increases and the light of the field diminishes as the reflectors are shortened. In his Chapter XIII example the aperture is 1/20 of the length, which for a one-inch instrument is under 2 mm. Any fixed assembly error occupies a larger share of so small an aperture.

What objects did the 1819 miniature kaleidoscopes contain?

Chapter XIV names no specific objects. It requires them to be as thin and slender as possible, brilliant in colour, and at the least possible distance from the reflectors. They sit behind a thin film of transparent mica, which Brewster prefers to glass for its toughness and elasticity at small thickness.

About Studio Yabaye

Studio Yabaye is the studio of Rocco (Roi) Ramon. I build brass kaleidoscopes and teleidoscopes. Each has a brass tube, cut, fitted and hand-finished in the studio, and front-surface mirror systems in several configurations. The range includes a pocket-size brass kaleidoscope 9 cm long. Each object wheel is poured and composed by hand, so no two pieces are alike. The studio is based in Israel and ships worldwide. See all products or contact the studio.