John Kerr (17.12.1824-18.08.1907) was a Scottish physicist and a Fellow of the Royal Society (1890). He was born in Ardrossan. He graduated from the University of Glasgow (1849) and worked there in 1857-1901.
His work was in the field of optics. In 1875 he discovered the phenomenon of double refraction in an isotropic substance placed in an electric field (the Kerr effect), and he found that optical anisotropy arises in liquid dielectrics under the influence of an electric field, which pointed directly to the existence of a connection between optical and electrical phenomena, one predicted long before by M. V. Lomonosov. The Kerr effect has found wide practical application, in particular as an optical shutter (the Kerr cell). In 1876 he also discovered a magneto-optical effect.