original late 19th century ornamental cast iron rococo style interior residential thermostat unit. the intricatley designed cover plate retains much of its original brass plated finish. internal mechanisms intact. the centrally located mercury thermometer with lightly incised brass scale plate. the first electric room thermostat was invented in 1883 by warren s. johnson. early technologies included mercury thermometers with electrodes inserted directly through the glass, so that when a certain (fixed) temperature was reached the contacts would be closed by the mercury. these were accurate to within a degree of temperature. fabricated by the powers regulator co., chicago, il.