388 Mr Russell on the Vibration of 



hard. Up to this period many persons from curiosity went across the 

 first span, and a few were seen at the further end ; but soon after mid- 

 day the lateral oscillations of the third span increased to a degree to 

 make it doubtful whether the work could withstand the storm ; and soon 

 afterwards the oscillating motion across the road-way, seemed to the 

 eye to be lost in the undulating one, which in the third span was much 

 greater than in the other three ; the undulatory motion which was 

 along the length of the road is that which is shewn in the first sketch ; 

 but there was also an oscillating motion of the great chains across the 

 "work, though the one seemed to destroy the other, as they did not both 

 (at least as far as could be seen) take place in a marked manner at the 

 same time. 



" At last the railing on the east side was seen to be breaking away, 

 felling into the sea; and immediately the undulations increased; and 

 when the railing on this side was nearly all gone, the undulations were 

 quite as great as represented in the drawing." — Lieut-Col. Reid, R, E. 



The reader who studies the principles I have explained in 

 the following paper, will perceive that the remedies I have 

 proposed, are those by which such destructive vibrations would 

 have been rendered impossible. 



My attention was directed to this subject, so important to 

 the arts, by having occasion, a few years ago, to erect a timber 

 scaffolding of considerable height, for experimental purposes, 

 in peculiar circumstances. There were many reasons which 

 rendered it proper to use very slender and very long pieces of 

 timber for this purpose, so as to come near to the utmost limits 

 that the structure would bear. Before it was removed a vio- 

 lent storm occurred, in which it suffered considerable damage 

 from the vibrations produced by the action of the wind ; and in 

 forming arrangements for remedying these injuries, and pre- 

 venting their recurrence, I was led to the examination of those 

 principles of vibration from which I have deduced the practi- 

 cal maxims that form the subject of this communication. After 

 detailing the circumstances which originally conducted me to 

 these conclusions, I shall explain the principles on which they 

 depend, and conclude the paper with some practical rules. 

 Although the whole subject is very extensive, reaching to all 

 the structures and mechanical arrangements in which vibration 

 is to be prevented, I have here applied it principally to suspen- 

 sion bridges, not only on account of their national and com- 



