The theory of the winds[659] is of a somewhat more intricate nature. After observing the quarter in which the sun rises on any given day, at the sixth[660] hour of the day take your position in such a manner as to have the point of the sun’s rising on your left; you will then have the south directly facing you, and the north at your back: a line drawn through a field in this direction[661] is called the “cardinal”[662] line. The observer must then turn round, so as to look upon his shadow, for it will be behind him. Having thus changed his position, so as to bring the point of the sun’s rising on that day to the right, and that of his setting to the left, it will be the sixth hour of the day, at the moment when the shadow straight before him is the shortest. Through the middle of this shadow, taken lengthwise, a furrow must be traced in the ground with a hoe, or else a line drawn with ashes, some twenty feet in length, say; in the middle of this line, or, in other words, at the tenth foot in it, a small circle must then be described: to this circle we may give the name of the “umbilicus,” or “navel.” That point in the line which lies on the side of the head of the shadow will be the point from which the north wind blows. You who are engaged in pruning trees, be it your care that the incisions made in the wood do not face this point; nor should the vine-trees[663] or the vines have this aspect, except in the climates of Africa,[664] Cyrenæ, or Egypt. When the wind blows, too, from this point, you must never plough, nor, in fact, attempt any other of the operations of which we shall have to make mention.[665] That part of the line which lies between the umbilicus and the feet of the shadow will look towards the south, and indicate the point from which the south wind[666] blows, to which, as already mentioned,[667] the Greeks have given the name of Notus. When the wind comes from this quarter, you, husbandman, must never fell wood or touch the vine. In Italy this wind is either humid or else of a burning heat, and in Africa it is accompanied with intense heat[668] and fine clear weather. In Italy the bearing branches should be trained to face this quarter, but the incisions made in the trees or vines when pruned must never face it. Let those be on their guard against this wind upon the four[669] days at the rising of the Vergiliæ, who are engaged in planting the olive, as well as those who are employed in the operations of grafting or inoculating.