Jean-Baptiste Biot, French physicist and astronomer, c 1850-1862.
© National Media Museum / Science & Society Picture Library
Stereoscopic daguerreotype of Biot (1774-1862), profesor of physics at the College de France and pioneer of polarimetry. Using a polarimeter (an instrument which measures the angle of rotation of a polarised plane of a beam of light when it pases through an optically active substance), Biot established the fundamental laws of the rotation of light polarisation by such optically active substances. He contributed to the recognition of the existence of a relationship between substances' optical activity and their molecular structure. This led to the development of a whole new group of scientific instruments, including the diabetometer, which is used to measure the sugar content in diabetics' urine. Biot also invented the polariscope, and made a balloon ascent to study magnetism at high altitudes.