=Wedge-shaped Isobars=, unlike V’s, usually point north. They are areas of high pressure moving along between two cyclones, being really projecting parts of an anti-cyclone. The fine weather accompanying them is only temporary, because they are never stationary, and are generally followed by cyclonic disturbances. At the narrow end of the wedge thunderstorms or showers often occur, and at the wide end fog is common. =Cols= or necks of relatively low barometric pressure occur between two anticyclonic areas. Like straight isobars they are intermediate systems. Over cols the weather is dull and gloomy; in summer they may be associated with thunderstorms. =Straight Isobars= obviously do not enclose any area of high or low pressure. They form an intermediate condition, preceding the formation of a cyclone; and are usually associated with a blustering wind and hard sky. =Weather forecasting= is necessarily somewhat difficult and uncertain. If one is dependent on _observations at a single point_ the following rules are useful:— (_a_) If the barometer falls slowly and steadily bad weather will follow. (_b_) The barometer falls for rain with S.W., S.E., and W. winds. (_c_) When the barometer falls rapidly, heavy storms may be expected. (_d_) The barometer rises rapidly for unsettled weather. (_e_) The barometer rises gradually for fine, settled weather. The _Thermometer_ also is of great value as a weather indicator, especially if one knows what is the average temperature at the place of observation for each day of the year. Thus:— (_a_) A temperature continued for some time above or below the average, indicates a probable change. (_b_) Electric storms follow unusual warmth in summer. (_c_) A low thermometer and almost steady barometer are succeeded in winter by gales from N.N.W. or N.E. The veering of the wind in England is also useful as an indicator. Thus:— (_a_) When the wind, in shifting, goes round in the same direction as the hands of a clock—_i.e._, from N. by E. to S., or from S. by W. to N.,—favourable changes of weather may be looked for. (_b_) When the wind _backs_—that is, veers round in the opposite direction—bad weather generally follows. The direction of the wind is an important factor. Thus: (_a_) Settled N.W. winds bring cold and fine weather. (_b_) Continued W. and S.W. winds are followed by rain. Clouds give useful indications. Thus:— A _mackerel sky_, that is, one covered with lines of cirrus clouds, causing halos around the sun and moon, presages rain in summer and thaw in winter. By degrees the light clouds descend and pass into either masses of cumulus, or into dense, horizontal stratus, which form at sunset and disappear at sunrise. Both these kinds pass into the grey, shapeless nimbus, which soon covers the entire sky and is followed by rain.