320 



but also the amount of extension and compression with a given 

 strain, indicates the existence of another element of resistance, in 

 addition to the resistances to extension and compression. 



The author then points out, that in applying the law of " ut 

 tensio sic vis " to contiguous fibres, under different degrees of exten- 

 sion and compression, the effect of the lateral adhesion has been 

 omitted, and each fibre has been supposed to be capable of taking 

 up the same degree of extension or compression as if it acted sepa- 

 rately, and independently of the adjoining fibres. 



It is then shown that this supposed independent action of the 

 fibres is inconsistent with other practical results, and evidence is 

 exhibited of a powerful lateral action when unequal strains are 

 exerted. 



From these and other considerations, the author is led to think 

 that the effect of the lateral action, tending to modify the effect of 

 the unequal and opposite strains in a beam, constitutes, in effect, a 

 " resistance to flexure " acting in addition to the resistances of 

 tension and compression. 



In order to ascertain whether the apparent difference in the 

 amount of tensile strength when excited by direct and transverse 

 strains is due to flexure, the author caused open beams or girders to 

 be made, each of which was formed by two bars of metal ; the upper 

 and lower bars of the same beam were in every case of the same 

 form and dimensions ; but the depth of metal and the distance to 

 which the bars were separated vertically, was varied in the several 

 forms of girder experimented upon. By these means the bar form- 

 ing the lower side of each girder was torn asunder under different 

 degrees of flexure. The different forms of girder experimented 

 upon were of equal length, and were compared with solid beams and 

 with bars of the same metal broken by direct tensile strain. 



From the mean of four experiments on each form of girder, the 

 value of the total resistance at the outer fibre is ascertained, and 

 exhibits the following results : 



1. In girders having the same depth of metal, namely about 2 

 inches, but the total depth of the girder, and consequently the 

 deflections different 



