OF IRON BEAMS. 487 



pace in cooling with the thinner part lower 

 down; and in those cases where the beam was 

 cast on its side, it would cool more regularly 

 with the sand in which it was buried. 



47. In the preceding experiments, it has been 

 mentioned, that we began with that form of 

 section which a highly ingenious modern writer 

 on the strength of cast iron, was induced to 

 consider as the strongest to preserve its elasticity, 

 the top and bottom ribs in it being equal ; and 

 this form we found to be j^th weaker to resist 

 an ultimate strain, than that of the common beam 

 in the iron on which he wrote, though it would, 

 as we have before seen, be perhaps, the strongest 

 in wrought iron. We then, by gradually reducing 

 the top rib in the same model and adding the part 

 taken off to the bottom one, obtained castings in 

 .which the^ strength was found to be regularly 

 increasing, and the form in experiment 3rd some- 

 what stronger than that of the common beam. It 

 did not now seem adviseable to decrease further 

 the top rib ; and as every beam had been found to 

 break by tension, or through the weakness of the 

 bottom part, I thought it best to keep increasing 

 the bottom rib by small degrees till such tinie as 

 the beam broke by the rupture of some other part. 

 This increase was commenced in experiment 9, 

 the ribs in that being as 4i to 1 ; and the result, 

 from the form of section, in this case was a gain 



