§ III. It was said in § V. of Chapter III. that we should not have occasion, in speaking of roof construction, to add materially to the forms then suggested. The forms which we have to add are only those resulting from the other curves of the arch developed in the last chapter; that is to say, the various eastern domes and cupolas arising out of the revolution of the horseshoe and ogee curves, together with the well-known Chinese concave roof. All these forms are of course purely decorative, the bulging outline, or concave surface, being of no more use, or rather of less, in throwing off snow or rain, than the ordinary spire and gable; and it is rather curious, therefore, that all of them, on a small scale, should have obtained so extensive use in Germany and Switzerland, their native climate being that of the east, where their purpose seems rather to concentrate light upon their orbed surfaces. I much doubt their applicability, on a large scale, to architecture of any admirable dignity; their chief charm is, to the European eye, that of strangeness; and it seems to me possible that in the east the bulging form may be also delightful, from the idea of its enclosing a volume of cool air. I enjoy them in St. Mark's, chiefly because they increase the fantastic and unreal character of St. Mark's Place; and because they appear to sympathise with an expression, common, I think, to all the buildings of that group, of a natural buoyancy, as if they floated in the air or on the surface of the sea. But, assuredly, they are not features to be recommended for imitation.[51] § IV. One form, closely connected with the Chinese concave, is, however, often constructively right,--the gable with an inward angle, occurring with exquisitely picturesque effect throughout the domestic architecture of the north, especially Germany and Switzerland; the lower slope being either an attached external penthouse roof, for protection of the wall, as in Fig. XXXVII., or else a kind of buttress set on the angle of the tower; and in either case the roof itself being a simple gable, continuous beneath it. [Illustration: Fig. XXXVII.] § V. The true gable, as it is the simplest and most natural, so I esteem it the grandest of roofs; whether rising in ridgy darkness, like a grey slope of slaty mountains, over the precipitous walls of the northern cathedrals, or stretched in burning breadth above the white and square-set groups of the southern architecture. But this difference between its slope in the northern and southern structure is a matter of far greater importance than is commonly supposed, and it is this to which I would especially direct the reader's attention.