The Refraction and Dispersion of Air for the Visible Spectrum

(a) Note on previously recorded values of the refractive index of air. For many centuries astronomers have recognized the effect that the refraction of the earth’s atmosphere has upon observations of the positions of celestial bodies. From the time of Tycho Brahe, when astronomical technique became sufficiently refined for the purpose, attempts have been made to apply corrections for the deviation of light in its passage through the earth’s atmosphere, and ultimately, in 1805, Delambre (1806) determined, by comparing a large number of astronomical observations, a value of the refractive index of atmospheric air for white light. The first accurate laboratory determination was made about the same time by Biot and Arago (1806), who measured the deviation of white light passing through air enclosed in a hollow glass prism. In 1857 Jamin (1857 b) made his original application of the methods of interferometry to the measurement of the refractive index of a gas. The increased accuracy obtainable by the use of the principle of the Jamin refractometer enabled Ketteler (1865) to determine the refractive indices of air for the red, yellow and green lines in the visible spectra of lithium, sodium and thallium respectively, and thus to make some of the earliest measurements of the dispersion of air.