1849.] Note on Iron Tension Bridges. 251 



time and thoughts so much in danger of being engrossed by it, at the 

 expense of more important matters, that I felt obliged to tear up what 

 notes I had written. I mention it now only to show that I never con- 

 ceived that the Memoir you printed for me in your number for January 

 1848 had entered upon the whole subject ; but only upon that part of 

 it which I took care to notify, and which appertains to the Quantity of 

 Metal required in the construction. 



P. S. — Since sending you the above my eye has alighted upon a 

 passage in Major Goodwyn's article, which explains various expressions 

 which he has in other parts used in reference to my Memoir, and 

 which before puzzled me much, as perhaps they have puzzled others 

 who may have read both communications. 



In opening the exposition of his " Resultant System,'* he says, 

 (p. 419) : — " I will now proceed to explain a system which only pro- 

 poses to do what the formulae in Mr. Pratt's Memoir says may be 

 done." But there are no formulce in my Memoir ; nor is any thing 

 said about formulae ; nor is any reference made to any ; nor inference 

 drawn from any. The Memoir is, as I have said, a mere piece of geo- 

 metry, leading to a remarkable general principle regarding the amount 

 of tension in a suspension bridge of any kind, Taper-Chain or not, and 

 therefore the quontity of metel necessary for its construction. The 

 demonstration stands alone, and is independent of all hypothesis regard- 

 ing the form of the bridge. 



This, therefore, convinces me that Major Goodwyn must have some 

 other paper in his mind : and that in writing his article he has had both 

 that and the Memoir before him, and has treated them as one. 



In 1843, when public attention was being called in India to the sub- 

 ject of Taper-Chain Bridges, I gave my voice decidedly against Mr. 

 Dredge's system, to friends with whom I conversed upon the matter, 

 as utterly impracticable, as well as unscientific : and I drew up some ma- 

 thematical formulae which might be applied to prove the truth of my 

 assertions, and also to calculate the strains in theory of the various parts 

 of a suspension bridge constructed upon any principle whatever. These 

 formulae where applied to several examples, among others to the projected 

 Balee Khal Bridge : and as they are now referred to for the first time 

 in your Journal (in the article I am noticing) I may mention as an 

 evidence of their correctness, that, among other results to which they 



