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JULY, 1915]
THE DOME IN PERSIA
with Persian tiles, some magnificent strips of which remain; it had doors of Indian steel which existed down to 1671 when they were seen and described by Struys,19 and both in planning and decoration, it would appear to have been the greatest masterpiece of Persian architecture. This is borne out by the universal chorus of praise showered on it by almost every traveller who has visited it. Morier, writing in 1810, in an age when few could see beauty outside the classical styles, said: "... of any description, and in any place, I do not recollect a building which could have surpassed this in its original state20."
I would invite special attention to the shape of this dome. Contrary to what is usually the case in the West, its beautiful outline is not obscured by the piling up of material on its haunches. This feature is typical of the general ignorance prevailing in Europe in regard to dome construction. Fergusson, with his knowledge of Eastern domes, was the first to shed a ray of light on the problem in 1855,21 when he made an attempt to point out one of the chief fallacies to be found in European theories of dome construction. Up till then the dome had been considered simply as a circular vault, and like a vault requiring a great amount of abutment. This error goes back to Roman times, as can be seen from the Pantheon, where perfectly unnecessary masses of material are piled up on the. haunches of the dome giving it a very ugly exterior outline (Fig. 12). Fergusson pointed out that while any given section of a vault was of the same breadth throughout, and therefore of the same weight, in a dome the lower rings are much heavier than the crown as they contain far more material. This is of course, in accordance with the curious mathematical theorem that the weights of
the sections of a hemispherical dome are in proportion to their heights. Thus, as is shown in Fig. 13, the weight of section A BCD is twice that of Section B C F because it is twice the height. Fergusson concluded therefore, that the weight of this lower ring constituted ample abutment, and that such a dome would be stable; in fact, as Fergusson expressed it, "It is almost as easy to build a dome that will stand, as it is to build a vault that will fall".
Fig. 12.
141
Fig. 13.
It was reserved, however, for E. B. Denison (afterwards Lord Grimthorpe) to give a full, complete and mathematical demonstration of the theory of the dome, when in February 1871, he read before the Royal Institute of British Architects a paper on "The Mathematical Theory of Domes", in which he brought the highest mathematical attainments to bear upon this problem. This use of the higher mathematics was rendered necessary by the fact that the actual thickness of the dome itself, interferes with the geometrical and trignometrical considerations involved in the problem, and so deranges all the natural relations of sines and cosines, that the formulae soon become unmanageable for any direct solution and render necessary a free use of the integral and differential calculus. I cannot here go into all the interesting results obtained by him,
19 Struys (J), Travels and Voyages, (trans.) London, 1684, r. 302. John Bell of Antermony who visited it in 1717 speaks of "a brass gate of lattice-work, seemingly of great antiquity." Travels from St. Petersburg, &c. London, 1788, I. 99.
20 Morier (James), A Journey through Persia, London, 1812, p. 258.
21 op.
cit. pp. 441-3.
