MEMOIR OF THE LATE PROF. E. HODGKINSON, F.R.S. 187 



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 

 eflPect. 



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 5 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. Ste- 

 phenson has used cast iron, for the purpose recommended 

 by Mr. Hodgkinson, with success in tubes of smaller di- 

 mensions than the Conway tubes. 



In 1847 ^^' Hodgkinson was appointed one of the 

 Commissioners to inquire into the application of iron to 

 railway structures ; and during the space of two years the 

 whole of his time and abilities were devoted to the subjects 

 of this inquiry. The exertions, both physical and mental, 

 which he made at this period for the advancement of 

 engineering science were so great as materially to afiect 

 his health and prostrate his powers. Immediately after 

 the publication of the Commissioners' Report in 1849, ^^ 



