1888.] 



On the Construe Lion of Suspension Bridges. 



347 



In most of the tombs the circle camiot be traced without diiliculty— the 

 stones of some of the squares incline outwards, in others they incline 

 inwards and form arches over the grAves. Recently workmen have been 

 employed by European gentlemen in digging up the interior of the 

 squares, and in a little tiine it will be impossible to trace the original 

 p]an, or form, of any of the tombs. 



The writer of this m.emorandum sa\Y one of the squares, or graves, 

 partly opened. At about two feet from the surface appeared a slab, 

 not of laterite, but granitic slone (an exotic ac the Red Hill^) cor- 

 responding in length and breadth with the size of the square ; this slab 

 was not removed, but it has been ascertained from unquestionable 

 authority (a gentleman who witnessed the removal of several of the 

 slabs) that under each slab is found an earthern vessel filled with 

 human bones — pieces of the broken pottery lie ab'out the tombs that 

 have been fully opened. 



There is no appearance of inscriptions on any of the stones ; the 

 inhabitants of the neighbouring villages have no tradition regarding the 

 tombs, in all probability, they existed previous to the introduction of 

 Hindooism. 



Madras, \4ith August 1838. 



VIII. — To the Editor of the Madras Journal of Literature and Science, 

 Sir,— In No. 18 of the Journal p. 120, I find that inadvertently I 

 have stated nine tons only per square inch of sectional area, to be the 

 supporting power allowed to bars of welded iron, while it is well 

 known that 27 tons is the average which is now taken as the standard for 

 the ultimate or breaking strength of cohesion of good malleable iron. 

 In all suspension bridges three times this strength is calculated for, that 

 is, " nine tons per square inch are taken as the strain that the chains of 

 " a suspension bridge may bear continually without any injury, and it 

 ".is prudent to proportion them for that strain." Vide Drewry, p. 19. 



I shall take an early opportunity of forwarding some transcripts of 

 experiments made by me for strengthening beams of wood by the ap- 

 plication of iron wire, and hope also to be able sliortly to declare that 

 iron may be eftectually preserved from rust by the appHcation of a 

 vegetable extract, which in this country is abundant and cheap. I 

 have tried it for a long time, and am most sanguine of complete 

 success. 



I remain, dear sir, 



yours faithfully, 



G. A. Underwood^ 



