American Heritage® Dictionary of the English Language, Fourth Edition
- n. An instrument that indicates changes in atmospheric humidity.
Century Dictionary and Cyclopedia
- n. An instrument or apparatus in which the hygroscopic property of some substance is employed for indicating approximately the humidity of the air, without attempting its accurate measurement. The most noted hygroscope is that of Saussure (also called the hair hygrometer), in which a prepared human hair, which expands or contracts in length according as the air is more or less moist, is made to move an index over a scale graduated from 0 to 100. By an adjusting-screw the index may be set at 100 whenever the air in the case is known to be saturated, and a fiducial point on the scale is thereby maintained.
GNU Webster's 1913
- n. (Physics) An instrument which shows whether there is more or less moisture in the atmosphere, without indicating its amount.
- n. hygrometer that shows variations in the relative humidity of the atmosphere
- hygro- + -scope (Wiktionary)
“In this way a small area of the surface of the earth is converted into a hygroscope, and these test surfaces tell us whether the ground is cooled to the dew-point or not.”
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