APPENDIX. 553 



venient to change the form of the objectionable 

 joints ; but bolts of more than three times the 

 strength (3 inch instead of 2 inch ones) have 

 been substituted for the others, and connected 

 so as scarcely to have any tendency to be bent 

 by leverage. 



The bridge, as it was, had stood some years, 

 daily crossed by carts, waggons, &c. ; and the 

 Royal Artillery, when in Manchester, had, I 

 understand, regularly crossed it with their horses, 

 guns, &c. when passing to and from Kersal 

 Moor. The joint that broke, and the others like 

 it, were doubtless much the weakest part; and 

 as these are now several times as strong as before, 

 it is probable the bridge will bear any weight to 

 which it is likely to be exposed, avoiding great 

 vibration. But when heavy weights are on 

 structures of this description, care should always 

 be taken to prevent vibration; which, if consi- 

 derable, offers, perhaps, one of the most serious 

 trials to which they can be exposed. The effects 

 of vibration on such structures do not seem to 

 have been sufficiently considered ; and the only 

 experiments on it, which I have seen, are the 

 interesting ones, by Mr. Telford, (Barlow's 

 Essay, on the strength of Timber, Appendix.) 



October, 1831. E. H. 



4 A 



