14 Report of a Plan for building 



giving it such an additional degree of strength, for by increasing 

 the quantity of iron, vou may gain any additional power. 



Mr. Telford snbmitted the whole of his experiments to the 

 examination of Mr. Barlow, who is the Mathematical Master at 

 Woolwich Academy, and who has published the greater part of 

 them in his work on timber and iron. Mr. Barlow states, that 

 the theoretical calculations which he has made, correspond with 

 those which are deduced from practical experiments. 



It appears by Mr. Telford's evidence, that the weight his ca- 

 bles will support before they will break is 2,016 tons, exclusive 

 of their own weight: the weight of the bridge, exclusive of the 

 cables, is 342 tons; therefore, the bridge will bear 1,674 tons 

 beyond its own weight. 



Mr. Donkin, on being asked whether it appeared to him that 

 the different calculations of strength made by Mr. Telford were 

 accurate ? replied, " Mr, Telford seems to have taken his pri- 

 mary data from the fact of a bar of iron, -one inch square, be- 

 ginning to stretch at half its absolute power ; in all the experi- 

 ments that I have witnessed of straining iron, I think none of 

 the bars began to stretch permanently under nearly two-thirds of 

 it ; it appears to me, therefore, that Mr. Telford's data are per- 

 fectly safe." 



4. Undulation and Side Vibration. — Mr. Telford says, there is 

 not much reason to expect undulation from any weight being laid 

 on any particular part of the bridge, in consequence of so great 

 a weight as 489 tons (the weight of the whole bridge) hanging 

 between the points of suspension; but to guard against it, he 

 proposes to make the four sides of the roadways of framed iron- 

 work, to be firmly bound together for seven feet in height, and 

 to have similar work for five feet in depth below the cables ; so 

 that when they meet towards the middle of the bridge, they will 

 constitute a frame-work of twelve feet deep on each of the road- 

 ways, which will also form a complete protection to passengers. 

 In respect to side vibration, Mr. Telford says, the proportion 

 which the breadth of the bridge bears to the length of it, will 

 keep it quite steady. 



Mr. Rennie says, " This bridge being to be covered with tim- 

 ber, it makes a single plank of 522 feet long and 30 feet wide; 

 and I conceive that the shock can scarcely be any thing side- 

 ways." And on his being asked by the Holyhead Road Commis- 

 sioners, " What effect do you apprehend the wind would have 

 upon a bridge of this construction r" answered, "My opinion is, 

 that from the strength of the iron and the weight of the bridge 

 taken together, there would l)e no injury in that way." 



5. Contraction and Expansion. — On these heads Mr. Telford 

 and Mr. Rennie calculate, there may be a rise or fall to the ex- 

 tent 



