MEMOIR OF THE LATE PROF. E. HODGKINSON, F.R.S. 179 



in the same manner as the strength of short solid pillars. 

 These formnlse, derived from experiments made with great 

 judgment and care^ embody onr present knowledge and 

 practice of cast-iron pillars for bearing-purposes. 



^^ The Power of Cast-iron Pillars to resist long-continued 

 pressure. ^^ 



Mr. Hodgkinson has recorded in this paper several very in- 

 teresting experiments on this subject. Two beams, rounded 

 at the ends, 6 feet long and i inch diameter, were cast of 

 Low Moor iron, No. 3. The first bore a weight of 1456 lbs. 

 during a period of from five to six months, and then broke. 

 The second broke with 1500 lbs. laid on immediately. From 

 this experiment Mr. Hodgkinson inferred that time has but 

 little, if any, influence on the strength of cast iron. 



This inference seems, at least to me, to be theoretically 

 correct. If the weight laid on the beam and its molecular 

 forces be statically equal, the forces will remain in this state 

 of equilibrium until the molecular forces are weakened by 

 the influence of unequal temperature or other causes. Our 

 knowledge, however, of this practical subject is indeed very 

 limited. The inquiry would amply repay any one who has 

 the ability, opportunity, and means to pursue it. Mr. 

 Hawkshaw has made some admirable remarks on this 

 subject, in his evidence before the Royal Commissioners, 

 in 1847 (s^® Report, p. 296). 



The opinion of experienced engineers appears to be, that 

 vibrations produced by continual impact and change of 

 temperature afiect the strength of iron to a greater extent 

 than a continued strain, which preserves the molecules of 

 the iron in the same fixed position. Mr. Rastrick, in his 

 evidence before the Commissioners, gives the result of an 

 experiment made by a friend, bearing on this question, at 

 Pontypool Iron Works. He hung a bar of iron, an inch 

 square, up by one end perpendicularly, and contrived a 

 small hammer to be continually hammering it ; after a 



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