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The Dew-point

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  P-272

2025-11-24

773

Demonstration. - Pour ether into a test tube until it is half full, and put a thermometer into it. Bend a tube at right angles and place in the test tube as in Fig. 1. Connect the short end with a long rubber tube and blow gently through the ether. The ether will evaporate and the temperature will rapidly fall. Watch the surface of the lower end

of the test tube and take the reading of the thermometer when moisture first appears on the outside. Now stop blowing through the ether, and its temperature will rise. Take a second reading of the thermometer when the moisture disappears. The average of the two readings will be the dew-point.  The dew-point is the temperature to which air must be lowered so that the vapor present will be enough for saturation. Fogs, clouds, rain, and snow result from a lowering of the temperature of the air below the dew-point. The most oppressive days in summer are those in which the air is nearly saturated with water vapor.