Mr. Seaward o)i Suspension Chain Bridges. 425 



The following were the results of the analyses : 



No. 1. No. 2. 



Silica 36-62 ... 36'73 



Alumina 7"53 ... 2*78 



Oxide of iron 22-18 ... 25-83 



Lime 13-80 ... 21-79 



Magnesia 1-95 ... 12-4<4 



100-08 99-57 



The amount of oxygen, calculating from these results, is as 

 follows : 



No. 1. No. 2. 



Inthesiiica 18-42 18-47 



In the alumina ^'■^Min^?! 1'30\ „ ^^ 



In the oxide of iron 6-80 j^"'''^ 7-62/ ^'"^^ 

 In the lime......... 8-93 | ^,^^ 5-12 j 



In the magnesia... 0-75 J 4-81 J 



The excess yielded by the analysis No. 1 is probably owing 

 to a portion of protoxide of iron which the fossil appears to 

 have contained together with the peroxide. The calculation 

 from the proportions of oxygen gives reason for this supposi- 

 tion. 



The mineraloffical formula of these garnets of Sala is 



m\^ + 



s. 



I 



LXXXIX. Observations on Suspension Chain Bridges ,- xuith 

 an improved Method of forming the supporting Chains or 

 Rods: accompanied "with a Drawing. By Mr. J. Seaward. 



To the Editors of the Philosophical Magazine and Journal. 



"DEING some time back engaged in examining the Plans 

 -'-' of a Suspension Bridge proposed to be erected in a di- 

 stant part of England, 1 was forcibly struck with what appeared 

 to me to be a great sacrifice of strength in the mode which 

 is usually adopted in forming the suspending chains of such 

 structures. 



Under this impression, I was induced to offer a plan for a 

 suspension bridge on quite a different principle; the peculiar 

 recommendation of which is to ensure much greater strength 

 and stability fiom a given quantity of materials, than what can 

 be obtained according to the present plan. My design was 

 shown to several scientific gentlemen, but a want of confi- 

 dence, I believe, prevented it from being adopted. My views 

 of the subject are however unchanged, and I am satisfied that, 



Vol. 62. No. 308. Dec. 1823. 3 II were 



