Land and Sea

To design a wind rose perfectly oriented with respect to a specific location, a circumference was traced and a gnomon stylus positioned in its center. In the course of a day the shadow cast by the gnomon would touch the circumference two times, once in the morning and once in the evening. Using a divider centered on the two tangent points with an opening equal to the distance between them, two arcs were drawn. The two arcs intersected at a third point which, joined to the base of the gnomon, furnished the north-south orientation. By removing the gnomon and centering the divider on each of the intersections of this line with the circumference and an opening equal to the distance between the two points, two further arcs were drawn. The straight line connecting their intersection with the center of the circumference provided the east-west line.

Because it is generated by the shadow of the gnomon, the resultant design of the wind rose appears reversed with respect to the familiar representation of the cardinal points. The south is seen at the top, and from this direction originates the southern wind called Auster. From the bottom comes the northern wind, called the Tramontana. The left indicates the east, source of the wind called Levante. From the right, coming from the west, is the Ponente. To make it more readable, we rotate the image to put north at the top and trace out the intermediate winds.

Centering the divider on the east and south points with an opening equal to their reciprocal distance, two arcs are drawn. The line starting from the intersection between the two arcs and passing through the center indicates on one side the southeastern wind, the Sirocco, and opposite the Maestro or Mistral, the wind coming from the northwest. Proceeding in the same manner with points south and west, we obtain the southwesterly wind called the Libeccio, and, from the northeast, the Gregale. Completing the subdivisions of the circumference results in the half- and quarter-winds, a total of thirty-two points on the wind rose.

Limited to the eight major winds, the wind rose was used not only for navigation but also in architecture in the orientation of buildings. The entire conformation of thirty-two points, associated with the magnetic needle, became the principal instrument used to orient sailors on the open sea.