The College of Optometrists

Newton's optical legacy was particularly profound in the field of spectroscopy. In 1666 Newton discovered that white light was made up of the basic colours of the spectrum. This disproved the earlier belief that colours were caused through white light being somehow modified. The sun, however, is not the only source of celestial light. Thus, in the late eighteenth century, William Herschel experimented with the spectra produced by the light from other stars. In 1783 he placed a prism at the eyepiece end of a 20-foot reflecting telescope and in 1798 he investigated light from six bright stars including Sirius and Arcturus.

 

In 1802 William Hyde Wollaston (1766-1828) refined Newton's prism experiment by reducing the light source to a narrow slit 1/20th inch wide. He noted dark lines across the spectrum and at first assumed that these were the divisions between the seven colours.

 

Joseph Fraunhofer (1787-1826) discovered hundreds of similar lines whilst testing glass telescope lenses. Eventually he counted 576. Fraunhofer had gained experience as an optician working at the Utzschneider optical institute near Munich. He also reproduced spectra in laboratory conditions that differed from that of sunlight in not being continuous ('bright-line' spectra, with dark gaps between the lines).

 

Gustav Robert Kirchhoff (1824-1887) explained Fraunhofer's discoveries in 1859. He established that sunlight is just one of a number of glowing forms of matter (liquid or solid) that produce a continuous spectrum; bright-line spectra are caused by gases. Each element, whether found in gaseous, liquid or solid form could be analysed and a different tell-tale set of line positions identified. It was now possible to determine the chemical composition of celestial bodies and this gave way to a new science of astro-physics.

 

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Some relevant instruments from the BOA Museum collection....

 

  

Top of our set of images is item LDBOA1999.327, a Spectrometer by Philip Harris Ltd of Birmingham made of black painted metal and brass with a tripod base. It is contained in a wooden case with a hinged door that opens at the front. The company that came to bear this name was originally based in the Digbeth area of the city and started by Thomas Ellis, a Surgeon, in 1817. At that time the person Philip Harris would have been only 15 or 16 years old. He joined Ellis in 1825. The company traded as a wholesale Chemical Laboratory Company occupying its Bullring site until 1889 moving to 144-146 Edmund Street at some time around the turn of the 19th and 20th centuries.

Next up is item LDBOA1999.3515 Grace's Spectroscope, made by John Browning, 63 Strand, London. This has a brass cylindrical body with screw lenses and milled adjusting wheel. Late 19th c. Mr Grace has recently been tenatively identified as a near neighbour and sporting friend of John Browing, after whom it seems he may have named the instrument.

 

This is a diffraction spectroscope. John Browning's Prismatic Instruments Catalogue (March 1923) states:

This instrument was originally designed for meteorological use and has for many years been known as Grace's Rainband Spectroscope, but is equally suitable for all the various purposes for which Direct Vision Spectroscopes can be used. It has greater dispersion than the miniature type and the mechanical focusing adjustment will be found useful for faint lines and bands as distinct from the well-marked absorption bands, for which the simpler patterns of the Miniature type suffice.

 

John Browning was noted for his fine spectroscopes though he also sold a wide range of other optical equipment. He was also the first President of the British Optical Association 1895-1900.

 

Our third image is item LDBOA1999.3516 a Rain-band spectroscope & case, late 19th c., made by John Browning, 63 Strand, London, with a brass cylindrical body,  telescopic tube and screw lenses. It is contained in cylindrical cardboard case with slip top and no surviving end pieces. It's quite short. That's a five-centimetre scale shown next to it.

 

A rain band spectroscope was for viewing the broad red band that raindrops produce in a spectrum; these were popular items, not necessarily for serious scientists. Note the wording of this advertisement for a slightly earlier instrument from an 1861 issue of Chemical News:

 

Crookes' Spectroscope...with the kind and valuable assistance of W. Crookes, Esqu. F.C.S. so well known for his successful researches upon the spectrum, we have been enabled to produce a most efficient, portable and convenient instrument...Crookes' Pocket Spectroscope for tourists...Spencer Browning and Co., Patentees, 111 Minories, E.C. Established 100 years.

 

Fourth and finally comes item LDBOA1999.2761, an example of Thorp's Spectroscope & case, by R. & J. Beck Ltd, London. A brass D.V. Diffraction Rendering Spectroscope, cylindrical, with adjusting wheel and brass screw-cap on the end. It also features a tiny round lens. Contained within a black leatherette hinged case with clasp, lined with blue velvet and purple silk, this is a beautifully presented object that it almost seems a pity to remove from its case.

 

To see a fine spectacle-mounted spectroscope for use by jewellers visit the September 2009 Object of the Month page.