This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 Excerpt: ...is often employed in popular hygroscopes. 146. Hygrometers.--Instruments intended for furnishing precise measurements of the state of the air as regards moisture are called hygrometers. They may be divided into four classes: --1. Hygrometers of absorption, which should rather be called hygroscopes. 2. Hygrometers of ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 Excerpt: ...is often employed in popular hygroscopes. 146. Hygrometers.--Instruments intended for furnishing precise measurements of the state of the air as regards moisture are called hygrometers. They may be divided into four classes: --1. Hygrometers of absorption, which should rather be called hygroscopes. 2. Hygrometers of condensation, or dew-point instruments. 3. Hygrometers of evaporation, or wet and dry bulb thermometers. 4. Chemical hygrometers, for directly measuring the weight of vapour in a given volume of air. 147. De Saussure's Hygrometer.--The best hygrometer of absorption is that of De Saussure, consisting of a hair deprived of grease, which by its contractions moves a needle (Fig. 88). When the hair relaxes, the needle is caused to move in the opposite direction Fig. 88.--De Saussure's Hygroscope. Fig. 89.--Mounier's Uygroscupe. by a weight, which serves to keep the hair always equally tight. The hair contracts as the humidity increases, but not in simple proportion, and Regnault's investigations have shown that, unless the most minute precautions are adopted in the construction and graduation of each individual instrument, this hygrometer will not furnish definite numerical measures. Fig. 89 represents Monnier's modification of De Saussure's hygrometer, in which the hair, after passing over four pulleys, is attached to a light spring, which serves instead of a weight, anil gives the advantage of portability. These instruments are never employed for scientific purposes in this country. 148. Dew-point Hygrometers.--These are instruments for the direct observation of the dew-point, by causing moisture to be condensed from the air upon the surface of a body artificially cooled to a known temperature. DEW-POINT INSTRUMENTS. 139 The dew-point, which is itse..
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