MEMOIR OF EATON HODGKIXSON. 221 



lars of this inquiry have escaped my memory, but I well remember that Mr, 

 Hodgkinsou showed, on the clearest i^eouietrical evidence, that the position of 

 the tension-rods was not only no additional support to the stability of the bridge 

 but positively aided its downfall. Tliis circumstance induced Mr. Ste])honson to 

 reconsider the construction of the bridg-e, and devise a new arrangement for these 

 auxiliary supports. It was at this time, and in consequence of the accident above 

 alluded to, that Mr. Robert Stej)henson made the personal acquaintance of Mr. 

 llodgkinson, the friend of his father, the man to whom he had steadily looked 

 as his authority and guide in the application of iron to railway purposes. When, 

 therefore, Mz. Stephenson was engaged in the novel construction of the Conway 

 and Britannia tul3ular biidges, he requested the assistance of his friend Mr. 

 Hodgkinson in fixing the best form and dimensions of tubes. The experiments 

 which were devised and earned out by Mr. Hodgkinson with a view to answer 

 the a1)ove questions are recorded in the report of the royal commissioners 

 ap]>ointed to inquire into the application of iron to railway structures. 

 Mr. Hodgkinson, by these experiments, sought — 



1. To ascertain how far the strain upon a square inch at the top and bottom 

 of the tube would be afiected by changing the thickness of the metal, the other 

 dimensions being the same. 



2. To ol)tain the strength of similar tubes. 



3. To find the strength of tubes of various forms of section in the middle, 

 and to furnish means of judging of the proper proportions of the metal in the 

 bottom, top, and sides of the tube. 



4. To ascertain the relative strength of uniform tubes to bear a weight in all 

 parts of their length ; and whether tubes, tapering in thickness from the middle 

 towards the ends, according to theory, would be equally strong in every part. 



5. To obtain the resistance of the tubes, previously tried vertically, to bear a 

 side pressure, with an intention to ascertain the effect of the wind upon a tube. 



6. To ascertain the strength of small tubes of difierent forms of section to 

 resist best a force of compression applied in the direction of their length. 



7. To ascertain the resistance of wrought-iron plates to a crushing force in 

 the direction of their length. 



8. To determine the strength of tubes to sustain impact, with reference to 

 riveting. 



9. To determine, by bodies let fall upon tubes, the probable effect, if any, of 

 trains rusliing rapidly upon tubukir bridges, to produce resilience, or springing 

 up at the ends. 



10. To determine the transverse strength of tubes stiflened in the top with 

 cast iron, joined with wrought iron, to increase the resistance of the top to a 

 crushing force. 



Tliese are important practical problems ; and when the issue is considered, viz.: 

 the continued stability of the Conway and Britannia tubular bridges, tliey 

 required for their solution great skill in the subtilities and artifices of mathe- 

 matical and experimental science. The answers which Mr. Hodgkinson obtained 

 to the abov(^ ])roblems were deenu'd by Mr. Stephenson to be so satisfactory as 

 to enable him with confidence to build the tubular bridges.- 



A concise but clear exposition of these answers is given by Mr. E. Clark 

 before the commissioners appointed to iiKpiire into the application of iron to ruil- 

 way piu'poses. (See report, ]>age 3.59. ) 



It was impossible that such assistance in the execution of a novel design 

 could be lightly esteemed or inad('([uate1y appreciated by the great engineer. 

 Hence, in the history of these tubular bridges, where ]Mr. Stej)henson is anxious 

 to record the merits of his assistants, he frankly acknowledges his deep obliga- 

 tions to the mathematical philosopher "for devising onl carn/i>iff out a scries of 

 experiments ivhich terminated in establishing the laics that regulate the strength of 

 iuhidar structures, in a manner so satisfactory that I was enabled to proceed ivith 



