Page:History of Indian and Eastern Architecture Vol 1.djvu/362

 DRAVIDIAN STYLE. BOOK III. light on the history of the invention, though this is not, of course, capable of direct proof. The simplest mode of roofing a small square space supported by four pillars is merely to run an architrave or stone beam from each pillar, and cover the intermediate opening by a plain stone slab. Unless, however, slabs of great dimensions are available, this mode of construction has a limit very soon arrived at. The next step therefore is to reduce the extent of the central space to be covered by cutting off its corners ; this is done by triangular stones placed in each angle of the square, as in Woodcut No. 172, thus employ- ing five stones instead of one. By this means, the size of the central stone remaining the same, the side of the square space so roofed is increased in the ratio of ten to seven, the actual area being doubled. The next step in the process (Woodcut No. 173) is by em- ploying three tiers and nine stones, instead of two tiers and five stones, which quadruples 1 7*- the area roofed. Thus, if the central stone Diagram of Roofing. -, . . c , is 4 ft., by the second process the space roofed will be about 5 ft. 8 in. ; by the third 8 ft. square ; by a fourth process (Woodcut No. 174) with four tiers and thirteen stones V V 173- Diagrams of Roofing the extent roofed may be 9 ft. or 10 ft, always assuming the central stone to remain 4 ft. square. All these forms are still currently used in India, but with four pillars the process is seldom carried further than this ; with another tier, however, and eight pillars (as shown in Woodcut No. 175), it may be carried a step further exactly the extent to which it is carried in the tomb at Mylassa above referred to. In this, however, as