412 Proceedings of the Society of Arts. 



F. R. S. E., M. S. A., civil-engineer and macbine-makerj Edinburgh. 

 (596.) 



2. On the Vibrations of Suspension Bridges, and other Structures^ and 

 the means of preventing Injuries arising from this cause. By John Scott 

 Russell, M.A., V.P.S.A. (690.) 



Mr Russell's attention had been directed to this subject, so important 

 to the arts, by having occasion some years ago to have a structure of 

 timber of great height and exceedingly slender, erected for experimental 

 purposes. The evils arising from oscillations had in that case been strict- 

 ly inquired into, and had led to the examination of the principles of those 

 oscillations and the best and simplest mode of obviating them. The case 

 of Suspension Bridges, was that to which these principles were most di- 

 rectly applicable, both on account of their extreme lightness and slen- 

 derness, and because their strength was so near the limits of possible co- 

 hesion that mere weight of materials would not in that case, as in most 

 others, supply the place of advantageous arrangement. The subject was 

 at present rendered highly interesting by the circumstance that both the 

 Suspension Bridges of Montrose and of Menai were, from this cause, im- 

 passable to her Majesty's mails, and public business was thereby much 

 interrupted. It was also in our recollection how recently the Brighton 

 Pier and other structures of a similar nature had suffered from the same 

 cause. The paper consisted, first, of an account of the author's original 

 experiments and observations on the oscillations of structures ; second, 

 of the philosophical principles on which they depend ; third, of the ap- 

 plication of these principles to Suspension Bridges and other structures. 

 It was shewn by some beautiful experiments, that the tendency of such 

 structures is to oscillate in equal portions like the string of a musical in- 

 strument in sounding harmonics, and that the great object in mechanical 

 structures was to stop these vibrations, whereas in musical strings it was 

 to continue and increase the vibrations, the principles were the same, 

 but the plans to be followed were opposite. It was, last of all, shewn, 

 that, by placing stays in certain positions' rather than others, they might 

 be so arranged as to give a bridge perfect stability. It appeared that 

 two stays, placed according to the rule, would give as much stability as 

 thirty-five in the common way, and that four stays would do as much as 

 one hundred — thus effecting great economy in weight and expense, with 

 great stability and £ trength. 



The following were admitted ordinary members : — 

 David Smith, Esq. W.S., 3 Doune Terrace ; Mr F. Watson, bookseller, 

 62 Prince's Street ; David Hunter, Esq. of Blackness, 67 Queen Street. 



2>^th January. — John Scott Russell, M.A., F.R. S.E., Vice- 

 President, in the chair. The following communications were 

 laid before the Society : — 



1. On an Expeditious Method of temporarily, but securely, stopping 



