Where the Winds Blow

King Aeolus, lord of wind and cloud, ruler of contending winds and moaning gales, controlled their fury lest they flay the sea into a great uproar. So great was his power, that Agamemnon, leader of the Greek expedition to destroy Troy, sacrificed his daughter Iphigeneia to secure a favorable wind for his voyage across the sea.

Winds, and the place from which they blew, were the earliest means of dividing the horizon into named parts in order to express direction. The ancients used various forms of wind systems: Homer described four winds, consisting of the four cardinal points we now call north, south, east, and west; Pliny and Posidonius recognized eight winds, whereas Aristotle enumerated twelve.

Mediterranean mariners named winds after the lands from which they originated, such as Greco (from Greece) to designate the northeast, or Africus for southwest. Other directions were named after the gods who reigned in that region. Astronomical positions, as well, were used to indicate wind direction. Septentrio designated north, since that wind blew from the direction of the seven stars in the constellation of Ursa Major--the north pointing big dipper. Sunset and sunrise at the summer and winter solstices filled in the intermediate points between the four cardinal directions, corresponding roughly to northeast, southeast, southwest, and northwest. Some wind names had no set bearing, but were identified and personified according to the weather they brought with them.

As if this nomenclature wasn't complicated enough, different names often indicated the same direction, or the same name for different directions. In Roman usage, Boreas reigned in the north; whereas to the Greeks, Boreas' realm was in the northeast. Septentrio, Tramontana, Hyperboreas, or Aquilo were all interchangeable for north.
 

Claudius Ptolemaeus (commonly called Ptolemy), greatest of all geographers and cartographers of classical antiquity, lived in Alexandria, Egypt during the second half of the second century AD. Successive editions of Ptolemy's Atlas, Geographia, continued to be produced in many editions in the fifteenth, sixteenth, and early seventeenth centuries as the basis of development in western cartography

On this Reisch 1504 version of Ptolemy's world, the four sides are embellished with personifications of the four primary winds, to which the cartographer gives their Latin and Greek names. Additionally, he uses the regional names of Septentrio, Oriens, Occidens, and Meridies. Meridies, designating south , is the position of the sun at its meridian--midday.
 

This world map, from a 1540/42 edition of Ptolemy's Geographia, shows the full twelve winds designated by Aristotle. The twelve-wind system remained throughout the Middle Ages as the one most commonly used. In keeping with the mythologic origin of winds for direction finding, they are of necessity placed beyond the confines of the known world--beyond the earth itself, in an outer, celestial sphere.
 

Over the centuries, an increased diversity of names for the winds and ambiguity about the direction they came from, produced a multitude of different wind systems. To create order out of the tangled confusion of names and directions, cartographers produced wind roses such as this by Jan Jansson in 1650. Thirty-two points (directions) are shown and labeled with various directional names for the winds. But to sailors plying the waters of the open oceans, a wind blowing from Thrace (Thracias) lost all relevance in defining direction. Eventually, the wind rose, overburdened by a multiplicity of names and obtuse symbolism, gave way to the directional system of north, east, south, and west, with their intermediate compounds, as used today.

Note the fledgling emergence at the perimeter of the circle of a more abstract directional system--degrees of arc of a circle. Even here, the cartographer is unable to resist introducing variations.
 

The wind rose appears late in the thirteenth century on sea charts (called portolan charts) of the Mediterranean. Gone now are personifications of the winds, to be replaced by a more abstract arrangement. The four cardinal directions of north, east, south, and west, are divided into eight primary winds, which are further divided into sixteen half-winds, and again into thirty-two quarter-winds. These equally spaced segments of eleven and a quarter degrees (11.25°) are marked by points. A network of fine lines radiate inward from the edge of the map to each of the points in the circle; the wind rose being the center in which all the lines intersect. Variously called rhumb lines, wind lines, or loxodromes, they are believed to function in aiding the navigator to project his course according to his destination and the direction from which the wind was blowing.

Although a conveniently simple arrangement, the problem nonetheless remained of what name to give to all the intermediate winds, or directions. In the time of Charlemagne the Great (AD 768-814), Frankish and Flemish mariners in the North had a different system of direction naming. They used the Teutonic monosyllabic words of Nord, Est, Sund and Oëst (North, East, South, and West) for the four cardinal points, and designated the remaining intermediate directions with simple compounds of these four words. This nomenclature was adopted for the standard directional schema, and is still in use throughout the world. It was supplemented in the nineteenth century by the addition of a circle marked in degree increments.

Mercator Projection Plan.

Cartographers conceived many methods for projecting the spherical surface of the earth onto the flat plane of a map or chart. There was no perfect answer; in some way all caused distortion, skewing relationships and distances. In 1569, Gerardus Mercator came up with a brilliant solution for mariners. He kept all the meridional lines (lines of longitude) parallel and equidistant from each other, instead of converging at the pole. To compensate for the greater space between the lines of longitude near the pole, he proportionally increased the distances between the lines of latitude from the equator toward the pole.

Although the relative sizes and shapes of landmasses are markedly enlarged and distorted as they become closer to the polar regions, the Mercator projection had one distinct advantage over all other projections: it allowed the navigator to plot a ship's course (rhumb line) that remained a straight line and a constant angle, no matter how it cu across the meridians. Technically called an isogonic cylindrical projection, it is now simply referred to as Mercator's projection. For ease of navigation, it has not been improved upon to this day.
 

Although this late version of Edward Wright's "Map of the World" shows land and some of its interior detail, it still can properly be called a chart, since the predominant emphasis is on those features relevant only to the navigator afloat. It contains the elements necessary to locate one's position on the ocean, and plot the course to a destination. A grid-plan of latitude and longitude, marked in degrees of arc, provides the former, and a compass rose, the latter.

Without the mariner's knowledge of wind and its general patterns, his sailing vessel is a lifeless object. Wright's depiction of the winds of the oceans is remarkably thorough and accurate. A broad band of fine, closely spaced lines shows the extent of the Northeast and Southeast Trade Winds (respectively north and south of the equator). Arrows within these bands indicate direction of the wind. Though unnamed, the doldrums are inferred at the Intertropical Convergence Zone by the complete lack of lines and arrows. The regions of Variables (sometimes called the Horse Latitudes), north of the Northeast Trades and south of the Southeast Trades, are prominently labeled. Note also, that Wright was quite aware of how the landmass of Africa altered the direction of winds along its shore.

Three things are missing on Wright's chart about wind systems in the North Atlantic. The Polar Easterlies, and the prevailing Westerlies north of the Variables are neither labeled, nor graphically shown. And although the seasonal pattern of the monsoons in the Arabian Sea is clearly traced, no mention is made of the seasonal variation in the Trade Winds.
 

By the end of the fifteenth century mariners extended their travels beyond the confines of the Mediterranean and began to explore the oceans of the world. By the mid-sixteenth century, all the major powers of the world--Spain, Portugal, France and England--were sending forth their ships.

In the desire to seek riches and expand their empires, nations of the world needed more than a wind system based on mythology of the ancients. Voyagers, in the great Age of Discovery, brought back with them new information and observations. General patterns of the ocean's winds began to be understood, and were placed on new charts of the world. Herman Moll's map of 1736 accurately depicts the extent and direction of the Trade Winds, the belt of Variables and Calms, as well as the seasonal variation of the Monsoons in the Indian Ocean. With this knowledge, a safe voyage and speedy return could be anticipated. The wind rose now becomes only a small, decorative element on the nautical chart.

One variant of the wind rose survives to the present day. Pilot charts for the Atlantic and Pacific oceans show the distribution of winds within each 5° area (three-hundred miles square) for each month of the year. Arrows show the direction of the wind, and the number of feathers on the shaft indicate its strength (on the Beaufort scale of wind velocity). Percentage of the time the wind blows from any direction is measured by the length of the arrow against a scale. The number in the center of the circle gives the percent of calms. This data is founded upon researches going back to the early part of the nineteenth century.