Illustrations of polarised light, 1817.
© Science Museum / Science & Society Picture Library
Illustration from 'Memoirs Acadamie Royal des Science De L'Institute de France', showing six circular figures illustrating various spectrums of colour. These are based on the experiments of Jean Baptist Biot (1774-1862), French physicist and pioneer of polarimetry, who discovered in 1815 that liquids, and some solids when disolved in water, are capable of rotating plane polarised light. He realised that a molecular property, or 'optical activity', must be causing these effects. Polarimetry, or the measurement of optical activity, is very useful for finding information about molecular configuration (shape).