A hygrometer in which the two thermometers are mounted side by side on a brass frame and fitted with a loose handle so that it can be whirled in the atmosphere to be tested. The instrument is whirled at some 200 rpm for about 1 min and the readings on the wetand dry-bulb thermometers recorded; used in conjunction with Glaisher's or Marvin's hygrometrical tables. It gives more consistent and accurate results than the ordinary instrument.