Atomic, molecular, and optical physics the origin of the index of refraction treated an electron in an atomic system classically according to the model of Paul Drude and Hendrik Lorentz. The theory was developed to attempt to provide an origin for the wavelength-dependent refractive index "n" of a material. In this model, incident electromagnetic waves forced an electron bound to an atom to oscillate. The amplitude of the oscillation would then have a relationship to the frequency of the incident electromagnetic wave and the resonant frequencies of the oscillator. The superposition of these emitted waves from many oscillators would then lead to a wave which
Some Girls Are Bigger Than Others performed live only once: at the final concert by the Smiths, at Brixton Academy, London, on 12 December 1986. The performance, which included a verse ("On the shop floor, there's a calendar, as obvious as snow, as if we didn't know") not used in the studio version, was recorded and later featured as a B-side on the 12" and cassette edition of the "I Started Something I Couldn't Finish" single in November 1987. Amateur footage of the entire concert has since appeared online. In Germany, "Some Girls Are Bigger Than Others" was released as a single in slightly edited form,