502 THE STRENGTH 



With regard to the elasticity there are some 

 anomalies; experiments 25 and 26 exhibited 

 no defect, when the first beam had borne 

 upwards of t, and the latter more than f the 

 breaking weight. But experiment 23, which 

 was on a beam of very small depth, shews a 

 deviation at an early period, it was however 

 very small till upwards of half the breaking 

 weight w^as laid on ; when perhaps the elasticity 

 of the bottom rib began to be injured. The 

 former defect being attributable to some incon- 

 siderable falling off in the elasticity of the com- 

 pressed part of the beam ; possibly arising from 

 oblique compression, through greater flexure 

 in a shallow beam. 



58. There seems, therefore, to be little doubt 

 that the elastic force is longer perfect in these 

 forms than in those on which experiments 

 have generally been made ; and the reason may 

 probably be this ; the earlier deflections in our 

 best beams are almost wholly caused by com- 

 pression, on account of the smallness of the 

 compressed part; and it appears highly pro- 

 bable that cast iron would remain perfectly 

 elastic under much greater forces when applied 

 directly to compress it, than would be required 

 to injure its elasticity by tension. 



