Some porticos again may be termed compound prostyles, because, while they project from the building, they also recede within it, as is the case with those of the London Post Office, University College, and Hanover Chapel, Regent Street ; and such an arrangement gives greater effect as well as spaciousness, and prevents the portico from looking like a mere addition to the front of a building. Besides the varieties above enumerated, there are those which are semicircular iu plan, of which the transept entrances of St. Paul's furnish very admirable examples; and another occurs in the pseudo-portico br portico-like compartment at the north-west angle of the Bank of England (fig. 10), which, owing to its being likewise recessed, and having columns behind those front (not arranged concentrically, but placed on the chord to the outer curve), produces a rich and picturesque effect. Beautiful however as the semicircular form is, it becomes unsuitable for such purpose if a portico so shaped cannot be made equal to a hexastyle, or a tetrastyle in antis, that is, have five intereolumne, because if there be only three, either the whole portico must be very narrow in proportion to its height, or the intercolumns so wide that the architrave over them will considerably overhang a line drawn from one column to another, and thereby produce an appearance both of deformity and weakness.
Respecting the temple-porticos of the ancients, or rather the external arrangement of columns in such edifices, whether confined to the ends or continued along the sides, we refer to the article TeneLx, where theirplan, to which we shall confine our attention, passing over all other circumstances. We shall not therefore attend to the order of columns employed in them, nor take any account of their dimensions, the plans being drawn not to the same scale, but for convenience sake, nearly to the same size. We commence with that of the Pantheon at Rome (fig. 1), attached to a circular edifice, and which, as will instantly he seen, is decidedly different from the usual portico at the end or front of a temple, or from those monoprestyles, or single external line of columns, which constitute the generality of modern porticos.
Besides being triprostyle, or having three open intereolumns on its flanks, it may be described as polystyle, having columns within, dividing it into three avenues or aisles, the centre one of which is extended by being considerably recessed, a circumstance that adds very greatly to the general effect.
As being, like the preceding, attached to a rotunda, we have selected fur the next plan that of the church erected by Canova at Possaguo (fig. 2). This also is a polystyle, though altogether different in its arrangement from the other, there being here merely a second range of columns behind those in front, on which account it might be designated a double octastyle.
they will be found sufficiently explained ; and shall now briefly pass in review some of the porticos that most deserve notice on account of As an example of a dec.astyle portico, we give that of University College (fig. 3), which instead of being merely monoprostyle, or single line of twelve columns, beneath a pediment, projects forwards very considerably, it being equal to a triprostyle, or a pseudo- triprostyle, with one intercolumn closed up, owing to which it appears internally to be partly recessed, to be carried out two intercolumna, and inwards for the space of one. This example is further remarkable on account of the unusual and picturesque arrangement of the steps forming the ascent up to it, which commence below on each side, while above they form a single broad flight, in such manner as to leave screeued areas, a a, which serve to admit light to the spaces in the basement beneath the portico.
The portico of the Glyptotheca at Munich (fig. 4) may be described es monoprostyle, recessed, and polystyle, it being compounded of an octastyle advanced only one intercolumn before the rest of the front, and of a tetrastyle in antis behind it, forming five open intereolumns, the extent of the recessed part, by which means not only great richness of columniation, but a picturesque play and con trast are obtained.
Like that of University College, the portico of the National Gallery (fig. 5) is pecudo-triprostyle, consequently projects as much as three intercolumns from the building; but, in other respects, differs very materially from it, being only partially recessed in the centre, where are two columns forming a distyle in antis. It also differs from the other example altogether in the arrangement of the steps leading up to it.
The portico of the Pantheon at Paris (Fig. 0) offers a more singular — -- — than judicious arrangement, two columns being projected at each end so as to produce a group of three at the external angles, which, although by no means displeasing 'in the ground-plan, produces an awkward effect in the structure itself or an elevation of it ; because, instead of being included beneath the pediment, these columns and their entablature form suer* little jutting-out bits, attached to the flanks, and almost suggest the idea of its being originally intended to continue them as lateral colonnades parallel to the hcxastyle beneath the pediment (as-in the next figure). Though this portico is only hexastyle in front, and has only four columns within, there are eighteen columns altogether, besides the half and three-quarter columns attached to the wall behind, a number sufficient to havo formed an octastyle triprostyle with six inner columns, namely, four disposed as in the portico of the Pantheon (Fig. 1), and two forming a promos recess for the centre doorway, as in Fig. 5.