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Friday, September 25, 2009

C V Raman is grt person

In the history of science, we often find that the study of some natural phe-nomenon has been the starting-point in the development of a new branch ofknowledge. We have an instance of this in the colour of skylight, which hasinspired numerous optical investigations, and the explanation of which, pro-posed by the late Lord Rayleigh, and subsequently verified by observation,forms the beginning of our knowledge of the subject of this lecture. Evenmore striking, though not so familiar to all, is the colour exhibited by oce-anic waters. A voyage to Europe in the summer of 1921 gave me the firstopportunity of observing the wonderful blue opalescence of the Mediter-ranean Sea. It seemed not unlikely that the phenomenon owed its origin tothe scattering of sunlight by the molecules of the water. To test this explana-tion, it appeared desirable to ascertain the laws governing the diffusion oflight in liquids, and experiments with this object were started immediatelyon my return to Calcutta in September, 1921. It soon became evident, how-ever, that the subject possessed a significance extending far beyond the specialpurpose for which the work was undertaken, and that it offered unlimitedscope for research. It seemed indeed that the study of light-scattering mightcarry one into the deepest problems of physics and chemistry, and it was thisbelief which led to the subject becoming the main theme of our activities atCalcutta from that time onwards.The theory of fluctuationsFrom the work of the first few months, it became clear that the molecularscattering of light was a very general phenomenon which could be studiednot only in gases and vapours but also in liquids and in crystalline andamorphous solids, and that it was primarily an effect arising from moleculardisarray in the medium and consequent local fluctuations in its optical den-sity. Except in amorphous solids, such molecular disarray could presumably