the ground he smoothed or levelled, so that the slabmay not be necessary. In the centre of this plane, forthe purpose of marking the shadow correctly, a brazengnomon must he erected. The Greeks call this gnomon<TKiadrjpas . The shadow cast by the gnomon is to bemarked about the fifth ante-meridional hour, and theextreme point of the shadow accurately determined.From the central point of the space whereon the gno-mon stands, as a centre, with a distance equal to thelength of shadow just observed, describe a circle.After the sun has passed the meridian, watch the sha-dow which the gnomon continues to cast till the momentwhen its extremity again touches the circle which hasbeen described. From the two points thus obtained inthe circumference of the circle describe two arcs in-tersecting each other, and through their intersection andthe centre of the circle first described draw a line toits extremity : this line will indicate the north and southpoints. One-sixteenth part of the circumference of thewhole circle is to be set out to the right and left ofthe north and south points, and drawing lines from thepoints thus obtained to the centre of the circle, we haveone-eighth part of the circumference for the region ofthe 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 letthe directions of the streets and lanes be determined bythe tendency of the lines which separate the differentregions of the winds. Thus will their force be brokenand turned away from the houses and public ways ; forif the directions of the streets be parallel to those of thewinds, the latter will rush through them with greaterviolence, since from occupying the whole space of thesurrounding country they will be forced up through anarrow pass. Streets or public ways ought therefore tobe so set out, that when the winds blow hard their vio-