Eaton Hodgkinson. 263 



' 4. The power of the tube to resist a vertical strain is to 

 its power to resist a strain on its side, as from the wind, as 

 26 to 15 nearly. 



' 5. The resistance of tubes to crushing follows the law 

 of cast iron pillars when the crushing force is not more 

 than 8 tons per square inch. It appears, however, that 

 cast iron was decreased in length double what wrought 

 iron was by the same weight ; but the wrought iron sunk 

 to any degree with a weight of 12 tons per square inch, 

 while cast iron required double the weight to produce the 

 same effect. 



' 6. The power of plates to resist buckling varies nearly 

 as the cube of the thickness. Mr. Clark refers to this 

 property as being most useful in the construction of the 

 tubular bridge. 



' 7. The tube bent* by pressure had borne a deflection of 

 five inches without serious injury ; but its riveting was 

 destroyed by repeated impacts deflecting it through less 

 than one inch. 



' 8. Resilience is perceptible, but very small. 



* 9. The introduction of cast iron on the top of the tube 

 would be attended with advantage in resisting the force of 

 compression. Practical objections, however, of a serious 

 nature prevented Mr. Stephenson from availing himself of 

 the power of cast iron to resist compression. He thought 

 it advisable to increase the thickness of wrought iron to 

 resist compression, rather than use a combination of 

 wrought with cast iron. It may be stated that Mr. 

 Stephenson has used cast iron, for the purpose recom- 

 mended by Mr. Hodgkinson, with success in tubes of 

 smaller dimensions than the Conway tubes. 



' In 1 847 Mr. Hodgkinson was appointed one of the 



