MEMOIR OF THE LATE PROF. E. HODGKINSON, F.R.S. 183 



ishing from the outside of the casting to the centre. Hence 

 it was justly inferred that the crushing, tensile, and trans- 

 verse strength of large castings would vary, being the 

 greatest towards the outside, and less towards the centre. 

 In cast-iron pillars of 2| inches diameter, the crushing 

 force varied from 39 tons per square inch outside to 33^ 

 tons per square inch centre. Mr. Hodgkinson discovered 

 that the difference in the strength between the outside and 

 centre of large castings is much less than in small ones. 

 Col. Sir Henry James found that the central part of bars 

 of iron planed was much weaker to bear transverse strain 

 than bars of the same size. By planing out f-inch bars 

 from the centre of 2 -inch square and 3 -inch square bars, 

 the central portion was little more than half the strength 

 of that from an inch bar. 



The fall of the railway bridge over the River Dee at 

 Chester, when several lives were lost, led Mr. Hodgkinson 

 to investigate the position of the tension-rods, which were 

 intended as auxiliary supports to the structure. The par- 

 ticulars of this inquiry have escaped my memory ; but I 

 weU remember that Mr. Hodgkinson showed, on the clearest 

 geometrical 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. This circumstance 

 induced Mr. Stephenson to reconsider the construction of 

 the bridge, 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 Stephenson 

 made the personal acquaintance of Mr. Hodgkinson, the 

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

 as his authority and guide in the application of iron to rail- 

 way purposes. When, therefore, Mr. Stephenson was 

 engaged in the novel construction of the Conway and 

 Britannia Tubular Bridges, he requested the assistance of 

 his friend Mr. Hodgkinson in fixing the best form and 



