43P 'THl:: £TRENaTU 



than making all the experiments on eaCh side 

 in a series would have done ; though it left the 

 tabular results rather more anomalous. I 

 preferred too, obtaining the extensions and 

 compressions from the same rib, to taking 

 each from different ones, on account of the 

 difficulty of getting such small castings pre- 

 cisely of equal size and equal strength of iron. 

 This mode of making the experiment, however, 

 rendered the time when the elasticity became 

 impaired rather doubtful, and I have set the 

 results down with regard to the set as they 

 appeared to me, but I place but little confi- 

 dence in them, particularly those respecting 

 compression. 



19. With regard to the inferences to be 

 drawn from these experiments, we will make 

 the three following suppositions : — 



1st. Suppose materials to be incompressible, 

 as has generally been assumed in this country, 

 and the experiment to be begun with the back of 

 the casting upwards, the leg DFE (figure tp 

 experiment i.) will, by supposition, offer an 

 insuperable resistance to a force tending to 

 compress it, and the deflection must arise from 

 the small quantity which the broad part ACB 

 will extend : if the casting be then turned the 



