Andronicos’ Tower was already an improved version of an ancient wind rose featuring just four directions.

In Mediaeval times, Italian mariners associated the wind rose with the compass and determined eight wind directions: north; north-east; east; south-east, south, south-west; west; and north-west. The four main points -north, south, east and west - are called cardinal points, cardinal deriving from the Latin for hinge cardo-inis as the ancients regarded them as the earth’s fundamental points.

Winds are generally known by the direction from which they blow, though some local winds have other names associated with their direction: the north wind in the Adriatic, for instance, is called tramontana and, from its Latin origin tramontanus ‘beyond the mountains’, we can deduce the direction it comes from; the easterly Mediterranean wind, on the other hand, is called levanter, deriving from the French lever, i.e. the point of sunrise. Some of the intermediate points also have names indicating the region they seem to blow from: to an observer in the middle of the Ionian Sea, the south-east sirocco would seem to come from Syria and the south-west libeccio from the coasts of Libya. Lastly, the north-west wind mistral is so named because it is considered the predominant wind in the Mediterranean (from the Latin magistralis (ventus), literally ‘master wind’).

Even today, wind direction is understood to be the direction the airflow comes from and can be indicated by means of the wind rose. Each quadrant, determined by the cardinal points, is divided into four equal parts. Hence we have 16 different directions, numbered starting from north and working clockwise.

Another, more approximate system for indicating wind direction is with reference to quadrants I, II, III and IV, numbered starting from north and working clockwise (e.g. quadrant I = winds between north and east).

Meteorologists instead use azimuthal subdivision, which goes from 0° to 360°. According to this system, a south wind, for instance, is a 180° wind.

Wind strength, namely the speed at which the mass of air moves, is measured in metres per second (m/s). Nonetheless, to accommodate the needs of air and sea navigation, the official unit of measurement in meteorology is the knot (kt), equivalent to a nautical mile/hour. In addition to these two units, kilometres/hour (km/h) and miles/hour are also in use (see table).

In the absence of instruments to indicate the direction and speed of wind, there are simple ways to make a visual estimate.

To determine direction, observing the behaviour of smoke, where possible, is a good method as it reveals even very slight air currents. Alternatively, follow the shadows of low clouds, the position of flags or the direction along which waves are blown.

Wind strength, on the other hand, can be determined approximately by observing the effects it has on things and objects found outdoors. This was the idea behind the Beaufort scale, a practical scale for measuring wind speed, named after its inventor Francis Beaufort (1774-1857). Beaufort was an Irish rear admiral and hydrographer who drew on his experience as a navigator to establish a scale of wind force from 0 to 12 based on the effects of the wind on the sea.

Instruments used to measure wind are called anemometers or anemographs (from the Greek anemos = wind and metron = measure or grapho = writing). In the meteorological field, since wind varies all the time near the ground, to compare the anemometer data provided by the various weather stations, it was decided that transmitters should be placed on a pole at a height of 10 metres above the ground, on level land free of obstacles.

The wind speed measuring instrument may be a Robinson’s anemometer with three cups, mounted about a vertical axis. The anemometer spins due to the resistance the wind encounters on the two sides of the cups - cups are concave on one side and convex on the other. The speed of rotation is directly proportional to wind strength. The element indicating direction, on the other hand, is a weathercock, which points into the wind. The anemometer’s speed of rotation and direction are transformed into electrical signals and conveyed along a telephone line to the data gathering and processing system in the weather station. At this point, they are converted into digital form and readings given on the relevant displays.

Said displays also give the average of the last 10 minutes and upper and lower limits of strength and direction when they deviate from the average values by 10 knots and/or 60° respectively. Another wind speed measuring instrument used quite widely is the propeller anemometer, which has an aerodynamic shape (like a plane) and whose theory of operation is exactly the same as its counterpart above.

Good wind measurements can also be achieved with handheld anemometers, the type that revolve and give a direct reading. Remember, though, that observation must be performed with the instrument pointed towards geographic north, established with the aid of the compass attached.

Bearing in mind that air at ground level is prevented from running a constant course at a constant speed by the unevenness of the earth’s surface, the wind is given various definitions depending on the changes it is forced to make.

It can be defined as a “steady wind” if fluctuations are slight; a “gusty wind” when speed increases by at least 10 knots for less than 20 seconds at a time whilst maintaining roughly the same direction as the average value; and a “swirling wind” when both direction and speed change continuously.