The phenomenon of the rainbow, which is caused by the splitting of "white" light from the sun into its colours by raindrops, can be reproduced by passing light through a prism. The spectral analysis of light is termed "spectroscopy".
In the 1860s, two German scientists, Robert Bunsen (1811-1899 - already mentioned in the context of the Bunsen burner - page 19) and Gustav Kirchoff (1824-1887) realised that different chemicals gave rise to characteristic spectral lines, even when they occurred in different combinations in a substance. They wrote: "It is well known that certain substances possess the property of imparting definite colours to flames in which they are heated. When the coloured light thus produced is analysed by a prism, spectra exhibiting differently coloured bands or lines of light are seen. Upon the occurrence of these lines of light an entirely new method of qualitative chemical analysis can be based - a method which greatly enlarges the scope of chemical reactions, and points to the solution of problems hitherto unapproachable" (Bennett 1984,4). One exciting consequence was the realisation that it would be possible to analyse the composition of the heavenly bodies, long before anyone could travel to them to find out at first hand.
The instruments in this section are all related to the taking and analysing of spectra. One of the major instruments in the entire collection is the "giant spectrometer" (014) used by Walter Noel Hartley (1846-1913) in his classical researches on the spectra of the chemical elements. (A spectrometer is a spectroscope with a divided circle or other scale, which allows the position of a line in a spectrum to be given a numerical value.) Although of English birth, Hartley moved to Dublin in 1879, where he was employed in the Royal College of Science in Merrion Street, now the Offices of the Taoiseach. He was the first person to establish that relationships exist between the wavelengths of spectral lines of the elements and their positions in the periodic table (published in 1883), and he studied also the relationship between the structure and spectra of a wide variety of organic compounds. This important work led to his election to Fellowship of the Royal Society in 1884, and to a Knighthood in 1911 (J. Burnett in Mollan 1990a,39). The giant spectrometer was made by the firm of Adam Hilger of London, leading maker of such instruments in the late nineteenth and for the first half of the twentieth century. It became Hilger & Watts in 1948 (Cattermole 1987,142).
This giant spectrometer is floor-standing on its own trolley. The more-usual instrument is the "Table" spectrometer (016), so-called because it can be used on a table or laboratory bench.
A very convenient type of spectroscope was introduced by Paris instrument maker, J.G. Hofmann, in 1862 (015) (Bennett 1984,8). This was the "Direct Vision" spectroscope, which uses a prism system consisting of two different types of glass - usually crown and flint glass, which have different indices of refraction. With this, a spectrum could be produced without the need to have collimator and telescope at an angle to each other.

010  Adjustable Slit
011  Hollow Prism   .
012 Light Recombination Mirrors
013 Spark Chambers
014 Spectrometer
015 Direct Vision Spectroscope
016 Table Spectrometer

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