io6 



Hygrodeik. An improved form of hygrometer (q.v.) with a 

 radial diagram and pointer from which the dewpoint is 

 determined. [4, IS, 16, 17, 21.] 



Hygrograph. An instrument for recording automatically the 

 variations of the humiditv of the atmosphere. [6, 15, 16, 17, 

 21, 27.} 



Hygrograph, Hair. A recording hygrograph depending on the 

 action of moisture upon a hair. [2, 6, 15, 17, .] 



Hygrometer. An instrument generally for measuring the state 

 of humidity of the air. [5, 6, 9, 13, 15, 16, 17, 19, 20, 21, 

 24, 25, 26, 27, 28.} 



Hygrometer, Daniell. A hygrometer in which the humidity of 

 the air is determined by noting the temperature at which 

 dew is deposited. It consists essentially of two thermo- 

 meters, one immersed in a volatile liquid which, by evapora- 

 tion, lowers the temperature to the dewpoint ; the other, 

 affixed to the stand, records the temperature of the uncooled 

 air. 



Hygrometer, for use in Cotton Factories. A form of Mason's 

 wet and dry bulb hygrometer (q.v.). [15.] 



Hygrometer, Horticultural. A wet and dry bulb hygrometer 

 with a special cylindrical scale revolving between the thermo- 

 meters, for ascertaining the likelihood of frost during the 

 night. 



Hygrometer, Mason's. Consists essentially of two thermometers, 

 suitably mounted, the bulb of one being kept wet, the other 

 dry. The evaporation of the moisture round the wet bulb 

 lowers the temperature, and the degree of humidity of the 

 air is determined, by the help of tables, from the difference 

 of the readings of the two thermometers. [15.] 



Hygrometer, Regnault's. A dewpoint hygrometer in which one 

 thermometer, immersed in ether, registers the dewpoint, 

 the ether being rapidly evaporated by a current of air. 

 The dew is deposited on a band of silver foil round the bottom 

 of the jar containing the wet bulb thermometer. 



Hygrometer, Self-Recording. A hygrometer fitted with a re- 

 volving drum and chart on which the variations of the two 

 thermometers can be continuously recorded. 



Hygrometer, Ventilating, Simmance and Abady's. A wet and 

 dry bulb hygrometer in which the two thermometer bulbs 

 are placed in the draught of air created by a ventilating 

 fan. See also Pagoscope. 



Hygrometric Balance. An instrument for indicating the relative 

 density of the air and consequent changes of rain or dry 

 weather, made in the form of a balance. [21.] 



Hygrophant. A hygrometer for ascertaining quickly the per- 

 centage of moisture in the atmosphere, without reference to 

 tables. 



