The weather indications.

The centers of areas of low barometric pressure, or general storms, are indicated on the map by the word "low," and the centers of areas of high barometric pressure by the word "high." The general movement of "lows" and "highs" in the United States is from west to east, and in their progression they are similar to a series of atmospheric waves, the crests of which are designated by the "highs" and the troughs by the "lows." These alternating "highs" and "lows" have an average easterly movement of about six hundred to seven hundred miles a day. The "lows" usually move in an easterly, or north of east, direction, and the "highs" in an easterly, or south of east, direction.

In advance of a "low" the winds are southerly or easterly, and are, therefore, usually warmer. When the "low" passes east of a place, the wind shifts to westerly or northwesterly with lower temperature. The eastward advance of "lows" is almost invariably preceded and attended by precipitation in the form of rain or snow, and their passage is usually followed by clearing weather. The temperature on a given parallel west of a "low" may be reasonably looked for on the same parallel to the east when the "low" has passed, and when the night is clear and there is but little wind, frost is likely to occur along and north of an isotherm of 40°. A "low" is generally followed by a "high," which in turn is followed by another "low."

By bearing in mind the usual movements of "lows" and "highs" and the general conditions referred to that attend them, coming weather changes may be frequently foreseen. "Lows" often move south of east from the Rocky Mountains to the Mississippi Valley, and then change direction to north of east. "Lows" of tropical or subtropical origin often move in a westerly direction to our south Atlantic and Gulf coasts, and then recurve to the northeastward. The centers of "lows" do not as a rule cross isotherms, but generally follow the general trend of the isothermal lines. Cold waves are always accompanied by, and forerun, "highs."

When isotherms run nearly east and west, no decided changes in temperature are likely to occur. When isotherms directly west of a place incline from northwest to southeast, the temperature will rise; when from northeast to southwest, the temperature will fall.

Southerly to easterly winds prevail west of a nearly north and south line passing through the middle of a "high," and also east of a like line passing though the middle of a" low." Northerly to westerly winds occur west of a nearly north and south line passing through the middle of a" low," and also east of a similar line passing though the middle of a "high."

An absence of decided and energetic "lows" and "highs" indicates that existing weather conditions will continue until later maps show a change, which usually appears in the west.