Kerr, WASHINGTON

CARUTHERS, 1827-1885. State Geologist of N. C. 1866-82; on U. S. Geological Survey 1882-83. Report, 1875-81. Kerria. Yellow-flowered shrub of the Rose family, native of Japan, much planted for ornament. Kerr's Law (ELECTRO-OPTICS). In 1875 Kerr observed that a dielectric under the influence of electrostatic stre becomes doubly refracting, and hence converts plane into elliptically polarized light. The law of the action is thus stated: tensity of electro-optic action of a given dielectric, i.e. , the quantity of optical effect (or the difference of retardation of the ordinary and extraordinary rays) per unit of thickne of the dielectric, varies directly as the square of the electric force." The optical effect may be measured by a compensator, and the potential difference by the Thomson electrometer.