Disposition and Spacing in Colonnades
The disposition of columns either in a façade or a colonnade is controlled by proportions which have been found to be desirable or are necessitated by special features of the order itself. The latter is the case with the Doric order, the spacing being determined by the trigylphs and metopes. If the triglyphs are placed centrally over the columns or pilasters the spacing of these apart will be two and a half diameters centre to centre, three and three-quarters, or five diameters, with two, three or four metopes respectively between them in the frieze. With the wider spacing of five diameters it is usual to employ coupled columns to add to the appearance of strength. As the triglyphs are one and a quarter diameters apart centre to centre, the coupled columns are brought very close together, entailing a slight modification of the bases. Since the ordinary projection of the plinth of a sixth of a diameter beyond the line of the shaft is not possible between the two columns, the plinth-blocks are united, and the torus moulding made slightly less in projection.
No. 171. Spacing of Columns.
The capitals being less in width are not affected, a small interval is left between the crowning reversa mouldings.
In the Ionic order the columns are spaced three and a quarter, three and three-quarters and four and a quarter diameters centre to centre. The coupled columns used with the wide spacing are one and a half diameters centre to centre or half a diameter apart at the lower extremity of the shafts.
The Corinthian spacing is slightly wider, three and a half diameters, four diameters, or with coupled columns four and a half diameters centre to centre. The coupled columns are placed as in the Ionic order one and a half diameters centre to centre.
It is desirable that attention should be given to the vertical alignment of the principal features. Dentils and modillions and indeed all strongly marked features should centre with the columns, and be equally spaced in the intervals.