A New Type of Secondary Radiation

IF we assume that the X-ray scattering of the ‘unmodified’ type observed by Prof. Compton corresponds to the normal or average state of the atoms and molecules, while the ‘modified’ scattering of altered wave-length corresponds to their fluctuations from that state, it would follow that we should expect also in the case of ordinary light two types of scattering, one determined by the normal optical properties of the atoms or molecules, and another representing the effect of their fluctuations from their normal state. It accordingly becomes necessary to test whether this is actually the case. The experiments we have made have confirmed this anticipation, and shown that in every case in which light is scattered by the molecules in dust-free liquids or gases, the diffuse radiation of the ordinary kind, having the same wave-length as the incident beam, is accompanied by a modified scattered radiation of degraded frequency. Motivated by Arthur Compton's observation that X-rays could lose energy when scattered inelastically by electrons (the 'Compton effect'), Raman and Krishnan hypothesized that a similar transfer of energy should take place when normal light is scattered by atoms or molecules. The 'Raman effect' was demonstrated in 1928 and now forms the basis of a powerful spectroscopic tool.