Corns, the north-west wind, and Aquilo the north-eastwind. Thus are expressed the number and names of thewinds and the points whence they blow. To find and laydown their situation we proceed as follows: let a marbleslab be fixed level in the centre of the space enclosed bythe walls, or let the ground be smoothed and levelled, sothat the slab may not be necessary. In the centre of thisplane, for the purpose of marking the shadow correctly, abrazen gnomon must be erected. The Greeks call thisgnomon (r%icx,@yigocg. The shadow cast by the gnomon is tobe marked about the fifth ante-meridianal hour, and theextreme point of the shadow accurately determined. Fromthe central point of the space whereon the gnomon stands,as a centre, with a distance equal to the length of shadowjust observed, describe a circle. After the sun has passedthe meridian, watch the shadow which the gnomon con-tinues to cast till the moment when its extremity againtouches the circle which has been described. From the twopoints thus obtained in the circumference of the circle de-scribe two arcs intersecting each other, and through theirintersection and the centre of the circle first describeddraw a line to its extremity: this line will indicate thenorth and south points. One-sixteenth part of the circum-ference of the whole circle is to be set out to the right andleft of the north and south points, and drawing lines fromthe points thus obtained to the centre of the circle, wehave one-eighth part of the circumference for the regionof the north, and another eighth part for the region of thesouth. Divide the remainders of the circumference oneach side into three equal parts, and the divisions or re-gions of the eight winds will be then obtained : then let thedirections of the streets and lanes be determined by the