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Teaching aids on double refraction and polarized light, 1820-1920

For at least two decades after R. Malus' 1808 discovery of polarized light,

experimental studies on its properties were chiefly the domain of scientists. This

included phenomena like double refraction, polarization by reflection,

interference effects in polarized light, and optical activity. Teaching on optics in

schools and colleges probably continued being limited to geometrical aspects of

rays, lenses, simple photometry, spectra and other aspects of light which could

be explained by I. Newton's corpuscular emission hypothesis.

Gradually however, means were developed by which students and

interested members of the public could experience for themselves the

remarkable range of visual effects produced by polarized light. The oldest

advertisement which I have found is from the workshop of H. Pixii in Paris,

1824. His catalog offers three different sets of apparatus for this purpose, one of

which is described below.

Another early producer of such educational material was J.W. Albert in

Frankfurt, who advertised Apparate zu Versuchen über die Polarisation des

Lichts in 1828. These included specially cut pieces of Doppelspath (Iceland

spar), an achromatized double-image prism, and thin plates of doppelspath,

aragonite, and quartz With a thin sheet of the dichroic mineral tourmaline on

each side of such plates, anyone could observe the different types of

multicolored interference patterns discovered by D. Brewster and others around

1820 in transparent respectively uniaxial, biaxial, and optically active crystals.

By the early 1830s the undulation theory of Huygens and Young, as

modified by A. Fresnel to admit transverse vibrations, had fully replaced

Newton's theory in the opinion of scientists. Sections on optics in Physics books

had to be rewritten and expanded accordingly.

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In 1855 the Abbé F. Moigno, a prolific writer on science, described the

situation twenty (and more) years earlier:

Il y a vingt ans, les phénomènes de la double réfraction, de la polarisation

rectiligne, circulaire, elliptique, mobile ou rotatoire, chromatique, de la

diffraction, des interférences étaient regardés comme inaccessibles... Moigno

mentions demonstrations of these phenomena which were performed for large

audiences in many cities by C. Despretz and others. He claims that they had

considerable effect towards reforming this important branch of physics.

A major step in the development of teaching aids, was H. Dove's 1835

description of a setup on a two-foot long brass bar for studying polarized light.

Dove's drawing of the setup is shown below on the left. It may have been the

first optical apparatus where Nicol prisms served both in a polarizing and

analyzing capacity. Light coming from the right is condensed by a large lens,

passing through the polarizer, other components and the analyzer to the viewer.

The inset shows fringes seen in a rapidly cooled plate of glass. Dove's device

was very popular for decades; in a report on an exhibition of scientific

equipment in 1867 it is called Dove's wohlbekannte Polarisationsapparat. In the

right-hand picture, taken from a 1909 textbook, the light comes from the left.

An analogous setup with a heater at one end and a thermoelectric sensor

at the other, was sold by e.g. N. Lerebours 1853 and E. Ducretet in 1905, both in

Paris. It was used for studying properties of heat rays, such as their polarization.

A wide selection of objects including polarizers for microscopes, plates of

ten different minerals, mirrors, and pieces of strained glass, is presented in a

catalog from A. Pritchard in London in 1836. A part of his list is shown below.

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Watkins & Hill in London published in 1838 a list of Apparatus for the

Polarisation of Light. Among items offered in this 1½ page advertisement were

double-image and Nicol prisms, a dichroscope and a polarizing kaleidoscope, a

hollow glass replica of an Iceland spar rhomb, piles of glass plates, a kit to

illustrate transverse wave motion, and the models listed below.

A device which was to become even more widespread than that of Dove,

was J. Nörrenberg's polariscope. It may have been first described in print in

1833, but similar instruments are also attributed to J.T. Mayer and J.B. Biot

much earlier. On the left, light is reflected down by the tilting glass mirror and

thereby polarized. It is then reflected from a metal mirror in the base up through

the glass mirror and through a platform on which transparent objects can placed

and rotated. The light is analysed upon reflection from a glass mirror at the top

which was often replaced by a Nicol prism as shown in the center picture, or a

thin plate of tourmaline as in the right-hand illustration. The latter instrument,

designed in 1839 by the optician H. Soleil in Paris, contained lenses and a

micrometer. By measuring the size of convergent-light interference figures (as

shown above) in biaxial crystal plates, the angle between these axes could be

found. These handy polariscopes were sold commercially from 1843 or earlier.

With later improvements such as Nicol-prism polarizers, they were featured in

many optics textbooks and apparatus catalogs into the 20th century.

With simple equipment, one could demonstrate the splitting of an

unpolarized light beam into two in Iceland spar. The right-hand diagram shows

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how the extraordinary beam will move around the ordinary one when a spar

rhomb is rotated about the direction of the incident light.

A second rhomb of spar, for instance in the holder invented by J. Jamin, will

replicate C. Huygens' discovery that the character of the light changes on

traversing the first rhomb.

Reflected sunlight was not always available for projecting optical

phenomena on to a large screen. Artificial illumination by oxyhydrogen flames,

coal gas, acetylene, electric arcs, and incandescent bulbs kept improving in the

19th century. The setup below is from an exhibition catalog in 1893.

Projectors were particularly useful for displaying the interference colors

in thin sections of minerals and rocks, with the aid of optional polarizing

attachments supplied by several makers. From a P. Pellin catalog, Paris 1900:

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The left-hand instrument below, designed by E. Munier-Chalmas, is in the same

Pellin catalog. The right-hand projector with accessories to study polarized light

and double refraction is from an E. Leybold Nachf. catalog c. 1908.

Pieces of Iceland spar which had been cut along particular directions and

polished, were a popular item in catalogs of educational optics.

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Dove's 1835 rack illustrated on p. 2 gave way in the late 19th century to more

sophisticated optical benches, like this one named after A. Paalzow:

Among other teaching aids was the Pickering polariscope, in the left-hand

illustration. It has a dark-glass polarizer at the base and a small Nicol prism in

the eyepiece. Simplified versions of polarimeters to observe optical activity in

organic liquids such as turpentine and sugar solutions were also offered.

This brief compilation is not exhaustive, but it shows that educational uses

absorbed a significant part of the Iceland spar crystals exported in 1820-1920.

Leó Kristjánsson, Dec. 2017