The section of the roll may be drawn thus: Draw the profile of the abacus and of the astragal. Then draw the exterior contour of the volute as far as its intersection with the line of the shaft, by establishing the cathetus and the first three points of the squares 1, 2, 3, and 1", 2", 3" in the eye. Draw a horizontal line e f mark ing the height of the center of the roll, fourteen parts below the abacus, and another horizontal three parts higher up. On the latter horizontal fix a point h. six and five-tenths from the edge of the volute; from this point, with a radius of three, a semi-circum ference may be drawn whose •intersection with the horizontal k gives the center of the second arc of the section, which may be drawn with a radius of six. Then continue the lower line of the abacus and mark a point o three and five-tenths beyond its pro jection; this is the center of a third arc of the circle which may be drawn with a radius of seven.
72. The principal figure of this plate (X) is the plan of the capital, which shows the horizontal form and the disposition of the rolls, as well as the combination of the circular mouldings with the square mass of the capital.
73. The Ionic capital is generally enriched with carved orna ments, the quarter-round is carved with eggs and darts, the bead of the astragal is carved with bead and reel ornaments and the roll is carved with leaves, more or less detailed, while a rosette is fre quently carved in the circle forming the eye of the volute.
74. The channels of the Ionic column differ from those of the Doric in the fillets which separate them; they are shown in this plate to be twenty in number, and the width of the fillet is equal to one-third of the width of the channel, so that, after having divided the circumference of the shaft into twenty equal parts, each of these is divided into eight, two of these eight parts being given to the fillet and six to the channel.
The plan of each channel is drawn from a center placed at a distance of one part outside of the circumference of the shaft, as is shown in the plate. (Plate X.) 75. The number of flutings of the Ionic shaft is frequently twenty-four instead of twenty, as here shown. In the attempt to differentiate between the Ionic and Corinthian capitals it is often desirable to allot a smaller number of flutings to the Ionic shaft. When this order is used at a small scale, it is very proper that the channels should be few in number, so as not to complicate the carving. For use in wood, however, twenty-four channels, with their centers placed on the line of the column circumference, are preferable, as they are sharper, more effective and better accord with the accepted number of seven flutingi for the pilaster shaft. The flutings as shown in plan on Plate X are very shallow and do not "tell" as much as should be expected of this method of ornamenting the column. It is therefore suggested that in actual practice the method and number of flutings shown on the plan of the Corinthian shaft, Plate XIX, be also employed on the Ionic.
76. The cornice of the Ionic order (Plate XI) is less compli cated than that of the Doric, having, with the exception of the dentils, none but horizontal divisions. The cornice is forty parts in height and its projection is equal to its height.
Certain of the mouldings are carved with the leaf and tongue, the egg and dart, and the bead and reel, the perpendicular divisions of which correspond to the axes of the dentils, which in turn correspond to the axes of the columns. The frieze is thirty parts in height and undecorated; the architrave is the same height as the frieze, and is composed of three bands or fascias and a crowning moulding. The band which rests on the capital is six in height and its face is plumb with the upper diameter of the column and with the frieze; the second band is seven parts in height and projects one part beyond the lower; between the second and third bands occurs a cyma-reversa two parts high; this third band has a projection of one and five-tenths beyond the second. The assemblage of mould ings crowning the architrave is composed of a bead moulding of one and five-tenths parts, and a cyma-reversa of three, crowned by a listel of two and five-tenths. The projection of these mouldings beyond the third band is three and five-tenths, so that the extreme projection of the architrave is six.