323. Section of Tomb of Mahmúd at Bijapur. Scale 50 ft. to 1 in.
Further assuming for convenience that the whole dome weighs 7850 tons, the outer rim will weigh 2826 tons, or almost exactly as much as the three inner rims put together; the next will weigh 2204, the next 1568, the next 942, and the inner only 314; so that a considerable extra thickness might be heaped on it, or on the two inner ones, without their preponderance at all affecting the stability of the dome; but this is the most unfavourable view to take of the case. To understand the problem more clearly, let us suppose the semicircle A A A ([Woodcut No. 324]) to represent the section of a hemispherical dome. The first segment of this, though only 10 ft. in width, will be 30 ft. in height, and will weigh 9420 tons; the next, 10 ft. high and 10 ft. wide, will weigh 3140; the third, 10 ft. by 6 ft., will weigh only 1884; the fourth will weigh 942; and the central portion, as before, 316.
324. Diagram illustrative of Domical Construction.
Now it is evident that the first portion, A B, being the most perpendicular, is the one least liable to disturbance or thrust, and, being also two-thirds of the whole weight of the dome, if steady and firmly constructed, it is a more than sufficient abutment for the remaining third, which is the whole of the rest of the dome.
It is evident from an inspection of the figure, or from any section of the dome, how easy it must be to construct the first segment from the springing; and if this is very solidly built and placed on an immoveable basis, the architect may play with the rest; and he must be clumsy indeed if he cannot make it perfectly stable. In the East they did play with their domes, and made them of all sorts of fantastic forms, seeking to please the eye more than to consult the engineering necessities of the case, and yet it is the rarest possible contingency to find a dome that has fallen through faults in the construction.
In Europe architects have been timid and unskilled in dome-building; but with our present engineering knowledge it would be easy to construct far larger and more daring domes than even this of Mahmúd’s tomb, without the smallest fear of accident.
The external ordonnance of this building is as beautiful as that of the interior. At each angle stands an octagonal tower eight storeys high, simple and bold in its proportions, and crowned by a dome of great elegance. The lower part of the building is plain and solid, pierced only with such openings as are requisite to admit light and air; at the height of 83 ft. a cornice projects to the extent of 12 ft. from the wall, or nearly twice as much as the boldest European architect ever attempted. Above this an open gallery gives lightness and finish to the whole, each face being further relieved by two small minarets.