The _Etesian Winds_ are drawn from the north across the Mediterranean by the great heat of the African desert. The _Mistral_ is a strong north-west wind peculiar to the south-east of France. The _Pampero_ is a north-west wind, blowing in summer from the Pampas of Buenos Ayres.
As long ago as the year 1600 Lord Bacon remarked that the preponderating tendency of the wind was decidedly to veer _with_ the sun’s motion, thus passing from N. through N.E., E., S.E., to south, thence through S.W., W.N.W., to N.; also, that it often makes a complete circuit in that direction, or more than one in succession (occupying sometimes many days in so doing), but that it rarely backs, and very rarely or never makes a complete circuit in the contrary direction. The merit of having first demonstrated that this tendency is a direct consequence of the earth’s rotation is due to Professor Dove, of Berlin, who has also shown that the three systems of atmospheric currents just treated of, viz., the constant, periodical, and variable winds, are all amenable to the same influence.
As to the _mode_ of observing the wind, Admiral Fitzroy recommends that a true east and west line should be marked _about the time of the equinox_, and the north, south, and other points of the compass being added, to take the bearings of the wind in relation to a dial so prepared, the indications of the _lower_ stratum of clouds in conjunction with vanes and smoke being preferred to any other.
The direction of the wind should always be given according to _true_, and not to _compass bearings_. Two points to the westward nearly represents the amount of “Variation of the Compass” for the British Isles, which yields the following table for the conversion of directions observed by the compass in Great Britain and Ireland to approximate true bearings.
+---------------------+-----+-----+-----+-----+-----+-----+-----+ |Compass bearings. N | NNE | NE | ENE | E | ESE | SE | SSE | |True bearings. NNW| N | NNE | NE | ENE | E | ESE | SE | +---------------------+-----+-----+-----+-----+-----+-----+-----+ |Compass bearings. S | SSW | SW | WSW | W | WNW | NW | NNW | |True bearings. SSE| S | SSW | SW | WSW | W | WNW | NW | +---------------------+-----+-----+-----+-----+-----+-----+-----+