Page:Handbook of Meteorology.djvu/183

 A hygrometer is useful in detecting increase of moisture, but it is not wholly essential. Where a hygrometer is available it is apparent that the less the difference between the wet bulb and the dry bulb the greater the moisture content of the air and the greater certainty of unsettled weather

The effects of increasing moisture in the air are so well known that the literature of them is great, and popular sayings concerning them are found in all ages.

It is well to bear in mind that these traditions apply to a more or less sudden change from dry to moist air, and not to the long-continued spells of moisture that come with steady sea winds.

Moist weather of long duration may be clear, as is commonly the case along the Atlantic Coast in summer; but a rapid change from dry to moist air almost always brings hazy conditions, and this is the sort of change that precedes rain.

The foregoing are only a few of the traditions and folklore sayings concerning the humidity of the air. Nearly all of them may be reduced to one or the other of two general principles—