The walls of the Greeks were of three kinds, named isodomum, pseudosodo mum, and emplection. The isodomum had the courses all of an equal thickness ; but the pseudosodomum had them un equally thick ; in both these walls, wher ever the squared work was discontinued, the interval or core was filled up with common hard stones, laid in the manner of brick, with alternate joints. The em plection was constructed wholly of squar ed stones ; in these bond stones were placed at regular intervals, and the stones in the intermediate distance were laid with alternate joints, in the same manner as tbose of the face ; so that this manner of Greek walling must have been much stronger than the emplection of the Ro man villagers. This is a most strong and durable manner of walling, and in modern times it may be practised with the utmost success ; but in the common run of build ings it would be too expensive.
Stone Columns. Stone columns should be executed with as few joints as possi ble ; if they can be procured in one piece, they will have a strong and grand effect. There should be no such thing as vertical joints ; for they not only destroy the beauty of the column, but are incon sistent with the laws of strength. Before the number of pieces can be fixed, two important circumstances must be taken into consideration : first, to find out those quarries which will produce durable stones, of the size and colour wanted, and the nearer to the place of erection the better ; next to inquire concerning the price of the carriage; if these come with in the maximum limit of what the proprie tor would chose to fix, then the number of pieces is determined ; but, if not, this number must be increased, in order to make it equal to, or less than, the pro posed sum, observing to choose the near est odd number. The circumstances be ing thus accommodated to each other, and the 'tones laid down at the place in tended for building, draw a section of the column through its axis, to the full size ; divide the height of this section, by lines parallel to the base, into heights equal in number to that of the stones ; by these means, the diameters of each end of eve ry stone in the altitude will be deter mined. The upper and lower bodies of each stone are first to be wrought exact ly to parallel planes ; and as one great beauty of columns is to make them ap pear, at a small distance, as if they were in one entire piece, they should be rub bed at first with a large coarse stone, in order to prevent the surface from being excavated, and then with a fine stone of the same size as the coarse one ; with the utmost care observing to try the straight edge, or rule, as the rubbing goes on ; in this the edge of the rule should always coincide with the surface, otherwise the two superficies which are to form the joint can never coincide.
The two beds of a stone being thus form ed, find the centre, and describe the cir cle at one end ; divide the circumference into a convenient number of equal parts ; (it is usual to divide it into six or eight ;) draw lines from each point to the centre; find the centre of the circle on the other bed, so that the two centres may be in the straight line forming the axis of the that is, when the straight line joining their centres is perpendicular to each bed, through the centre of this last circle draw a straight line, parallel to any one of the lines drawn through the cen tre and circumference of the former; also from the point in the circumference of the last drawn circle, where the line drawn through the centre cuts this cir cle, divide the circumference into the same. number of equal parts as that of the circle formerly drawn ; then draw lines from the centre to each of the points so divided, and these lines will be respec tively parallel to those of the former cir cle; the extremities of each pair of pa rallel lines, in each circumference, will regulate the chissel draught, which is to be wrought along the surface of the co lumn. The corresponding draught be ing made from each pair of parallels, the spaces between will be more easily wrought down ; then, if the number of pieces which compose the column ex ceed seven or nine, a straight edge may be applied, the side of which always be ing in a plane p'assing through the axis; but if fewer pieces are used, make a di minishing rule, that is, to the line of the column : on the side of the diminishing rule draw a straight line parallel to the axis ; this rule will serve to plumb the stones in setting them, and to work the convex surface of each stone : prepare another rule, equal in length to that of a stone having its edge straight the same as the diminishing rule.
The cement used in setting each co-' lumn stone is either oil-putty, or white lead, or white lead mixed with chalk putty, or fine mortar, or milled lead rolled very thin. If the column be large, and rolled lead be used, it needs only to form a ring half an inch distant from the edge of the joint, and let the joint at the edge be filled with oil-putty.