ss 



constructed j in my opinion, more strength is also 

 produced from less iron than in any that I previous- 

 ly knew of. I have recently seen one erected by 

 him in 1823, for Colonel Chalmers, at Glenericht, 

 the country seat of that gentleman. The span of 

 which is 104 feet, the road 10 feet wide, with a car- 

 riage way in the middle, and a narrow footpath on 

 each side. This bridge is capable of bearing any 

 weight that can be put on it ; indeed, the first trial 

 was seven loaded carts, each drawn by one horse, 

 so as they could be all on it together. 



This bridge is supported by two strong chains un- 

 der the roadway, each of them proved, before put- 

 ting up, to carry a strain of 25 tons ; but the prin- 

 cipal strength lies in twenty-eight suspension rods, 

 each of them was also proved, before being put up, 

 to carry 20 tons ; so that the strength is superior in 

 a tenfold degree to any weight that can go on it. 



Notwithstanding the great strength produced, ow- 

 ing to the way it is constructed, there are only 2 tons 

 of fine iron in the suspension rods, bottom chains, 

 back stays, and every thing else in anyway suspend- 

 ing or bearing the strain of that ponderous weight ; 

 and about 3 tons more of common English Iron, ap- 

 plied, in main posts, at the ends, (to save mason 

 work,) and the cross beams or joists for supporting 

 the road-way, and other parts where tenacity is not 

 required. 



All parts of this bridge contribute jointly to the 

 general strength, as well as severally to that of their 

 respective places; and any part, except the main posts, 

 may be taken away at pleasure without weakening 

 the general structure, more than the mere use of that 

 part taken away ; which must be of great use in case 



