The Kaleidoscope Craze: 200,000 Sold in Three Months
By Rocco (Roi) Ramon - licensed architect, founder of Studio Yabaye
A number often quoted in kaleidoscope history is 200,000. It is the estimate of instruments sold in London and Paris within three months of the kaleidoscope becoming public. It is usually repeated without its source and without the sentence that follows it in the original text.
This article goes back to that source: David Brewster's "A Treatise on the Kaleidoscope" (Edinburgh, 1819), written while the episode was still recent. It sets out what Brewster recorded about the demand, what he recorded about the copies, which makers he authorised, and what the episode shows about mirror alignment and angle accuracy. The patent and the priority dispute are covered separately in the history of the kaleidoscope.
Where the 200,000 figure comes from
The figure appears in the unnumbered introductory section of the 1819 Treatise, which carries the running head "History of the Kaleidoscope". Brewster writes that "no fewer than two hundred thousand instruments have been sold in London and Paris during three months".
Three points about this sentence are often lost when it is repeated:
It is an estimate, not a count. Brewster attributes it to the computation of those he considered best able to form an opinion. He does not name them and gives no sales records.
It covers two cities. The figure is for London and Paris together. The 1819 Treatise gives no separate number for either city and no number for any other place.
It covers three months, without dates. Brewster does not say which three months, and the Treatise attaches no calendar date to the sales period.
The period can only be bracketed. The British patent, no. 4136, was granted in July 1817. The earliest letter printed in the Appendix of the Treatise is dated 19 May 1818, and the dedication of the book is dated 22 March 1819. The three months therefore fall between mid-1817 and early 1819. The Treatise does not narrow it further.
How the instrument escaped before it was on sale
Brewster's account of the leak is short. He had decided to protect the instrument with a patent, because he expected it to serve the ornamental arts and to become a popular instrument of amusement. Before any number of the patent instruments could be prepared for sale, one of them was shown to some London opticians. Its properties became known, and other people started making it.
He writes that the sensation this caused in London could not be described. The speed followed from the construction. In its simple form, the instrument described in the Treatise is two reflecting plates in a tube, with loose pieces of coloured glass in a cell at the far end. A copy that produces some multiplied pattern can be assembled from two strips of glass by anyone who has seen one.
A footnote in Chapter XVIII records a second channel. According to Brewster, the patent specification was printed in a journal under the title "Directions for making the Kaleidoscope" and presented as an original communication, with the name of the patentee and the technical parts left out. He reads this as an apparent attempt to promote the belief that there was no patent.
Brewster's own verdict on the 200,000
The sentence that follows the sales figure is the relevant one for build quality. Of the 200,000, Brewster writes, "there is perhaps not one thousand constructed upon scientific principles". On his own estimate, that is at most 1 instrument in 200.
He adds a second estimate. Of the millions of people who had seen the effect, he believed that perhaps not a hundred understood the principles of the instrument or could distinguish what he calls the spurious instrument from the real one.
This is the stated reason for the book. Brewster writes that under these circumstances he thought it necessary to draw up a short treatise explaining the principles and construction of the instrument, the different forms in which it is fitted up, and its use in the useful and ornamental arts.
The Appendix shows that the problem was also a legal one. Brewster notes that the subject "must soon come under the notice of another tribunal than that of the public", and prints the opinions of four scientists - Professor Wood of Cambridge, James Watt, John Playfair and M. A. Pictet - on the difference between his instrument and earlier combinations of plane mirrors. Pictet, Professor of Natural Philosophy at Geneva, writes that he had lately witnessed the invasion of Brewster's rights as an inventor in London.
What was optically wrong with the copies
The introductory section does not list the defects of the copies one by one. It states the standard instead. Brewster sets out three conditions for a symmetrical picture, and the later chapters explain what happens when each is missed. The six points below follow from those chapters.
1. Wrong mirror angle. The first condition is that the reflectors stand at an aliquot part of a circle - an angle that divides 360 degrees exactly. For irregular objects such as loose glass fragments, it must be an even aliquot part: 45, 36 or 30 degrees for 8, 10 or 12 sectors. At any other angle the last reflected sectors do not join and the pattern shows a broken seam. The arithmetic is covered in kaleidoscope mirror angles.
2. Angle set by eye, not by test. Chapter VI gives a setting procedure. The tube is aimed at a line lying very obliquely to one reflector, and the plates are opened or closed until a star forms in which all points are equally complete and no lines are disunited. Only then are the plates fixed, with small brass arches filed to fit the space between the open ends of the plates.
3. Poor junction between the plates. Chapter V calls a good junction of the two reflectors the feature "on which the excellence of the instrument so much depends". Chapter VI requires edges that are straight and free from chips, and describes grinding a rough edge on a flat surface with very fine emery. A chipped or gapped junction shows at the centre of the pattern, where all sectors meet.
4. Object in the wrong plane. The second condition is that the object is in contact with the ends of the reflectors. Chapter IV shows that when the object sits beyond that plane, the sector seen directly no longer coincides with its reflected images, and the figure loses its symmetry. The introductory section adds that the deviation increases with the distance of the object.
5. Eye in the wrong place. The third condition is that the eye sits as near as possible to the angular point of the mirrors. Brewster states that this is the only position from which the direct and reflected images have the same form and the same magnitude. A wide or badly placed eye hole lets the viewer look from other positions.
6. Doubled images from mirror glass. Chapter III notes that ordinary mirror glass gives two series of images, one from the first surface of the glass and one from the metallic coating behind it. Their imperfect coincidence increases with the thickness of the glass. Brewster therefore assumes reflection from a polished metallic surface or from the first surface of glass.
Who the makers were
No copyist is named in the 1819 Treatise. Brewster refers to the copies only as a group, and Pictet refers to the invaders of the patent. Their number, trades and locations are not given.
The authorised makers are named. A notice on the last page of the Treatise lists the firms that made and sold "The Patent Kaleidoscopes":
London - P. and G. Dollond; W. and S. Jones; R. B. Bate; Thomas Harris and Son; Bancks; William and Thomas Gilbert; Berge; Thomas Jones; Blunt; Schmalcalder; Watkins and Hill; Smith; Spencer, Browning and Rust.
Birmingham - Philip Carpenter.
Bristol - C. Beilby.
Liverpool - Egerton Smith and Co.
Edinburgh - John Ruthven.
That is 13 London firms and 4 outside London. Several appear inside the book as designers in their own right: Chapter IX describes Bate's polyangular instruments, in which the reflectors can be fixed at any angle, and Chapter X describes Dollond's annular and parallel kaleidoscope and John Ruthven's universal kaleidoscope. The title page records that the book was printed by J. Ruthven and Sons.
What the episode shows about build quality
The episode shows an optical product that is easy to approximate and hard to build correctly. Two mirrors at roughly the right angle give a pattern. Two mirrors at exactly the right angle, with a clean junction, a correctly placed object and a correctly placed eye, give a closed, symmetrical figure. The difference is in tolerances, not in the idea.
The same variables decide the image today. The mirror material has changed: a front-surface mirror reflects from its coated face, so the second series of images Brewster described does not form. The angle, the junction and the object plane are still set at assembly, and an error in any of them is visible in the pattern.
At Studio Yabaye, I build each instrument from a brass tube, cut, fitted and hand-finished in the studio, with front-surface mirror systems in several configurations, including two-mirror and three-mirror. The checks below apply to any kaleidoscope from any maker.
Checklist: testing a kaleidoscope against Brewster's conditions
Count the sectors. In a two-mirror instrument with loose objects the count should be a whole even number: 8, 10 or 12 are the cases Brewster names.
Look at the last seam. Find the sectors furthest from the directly seen wedge. Lines crossing them should continue without a step or a gap.
Aim at a straight line. Point the open end at a straight edge at an oblique angle. The star should have equal points with no broken lines.
Look for doubled edges. A faint second outline next to each reflected edge indicates reflection from two surfaces of the mirror.
Compare direct and reflected sectors. If the directly seen sector differs in size from its reflections, or does not join them, the object plane or the eye position is off.
Use the right light. Kaleidoscopes need direct, preferably strong light, not side light.
Further criteria are in what to look for when buying a kaleidoscope.
FAQ
How many kaleidoscopes were sold in the first craze?
Brewster's 1819 Treatise gives an estimate of no fewer than 200,000 instruments sold in London and Paris during three months. He attributes the number to unnamed people he considered best able to judge. He gives no separate figure for either city and does not date the three months.
Where does the 200,000 kaleidoscopes figure come from?
The primary source is the introductory section, headed "History of the Kaleidoscope", of David Brewster's "A Treatise on the Kaleidoscope", printed in Edinburgh in 1819. It is an estimate reported by the inventor, not a sales ledger. Later accounts that give the figure of 200,000 repeat this one passage.
Were the 200,000 kaleidoscopes made by Brewster?
No. Brewster states that a patent instrument was shown to London opticians before any number could be prepared for sale, and that the design then became known. By his estimate, perhaps not 1,000 of the 200,000 were constructed on scientific principles, which is at most 1 instrument in 200.
What was wrong with the imitation kaleidoscopes?
Brewster's Treatise sets three conditions for a symmetrical image: a mirror angle that is an exact aliquot part of 360 degrees, an object in contact with the mirror ends, and an eye placed as near as possible to the angular point. An instrument that misses any one of them shows images that fail to join.
Who were the authorised kaleidoscope makers?
The last page of the 1819 Treatise lists 17 firms making and selling the patent kaleidoscope: 13 in London, including Dollond, Bate, and W. and S. Jones, plus Philip Carpenter in Birmingham, John Ruthven in Edinburgh, and one firm each in Bristol and Liverpool. Bate, Dollond and Ruthven also designed their own variants.
How did Brewster set the mirror angle accurately?
Chapter VI of the 1819 Treatise describes aiming the tube at a line lying very obliquely to one mirror and adjusting the plates until a star with equal, unbroken points appears - 4, 5 or 6 points for 45, 36 or 30 degrees. The plates are then fixed with fitted brass arches.
About Studio Yabaye
Studio Yabaye builds brass kaleidoscopes and teleidoscopes. Each has a brass tube, cut, fitted and hand-finished in the studio, and front-surface mirror systems. 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.
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