to Transverse Strain in Seams. 403 



The deviation in the position of the neutral axis from the 

 centre of the section under the smallest load, 5786 lb. at 

 centre of beam, must be supposed to be due either to the 

 points at which the extension and compression were measured 

 not being accurately distanced vertically, or to some in- 

 equalities in the resisting power of different parts of the 

 section. In any case these conditions will remain the same 

 for the same beam under the different loads. 



But it will be seen that there is a sensible and increasing 

 displacement of the neutral axis with increasing loads in the 

 direction of the compressed side of the beam, it being *121 inch 

 higher with 10,266 lb. than with 5786 lb., and -139 inch 

 higher with 14,746 lb. than with 10,266 lb., giving a total 

 displacement of '26 inch, or more than \ inch. 



A similar result is shown by an experiment with another 

 similar beam loaded successively with 8000 and 16,000 lb. 

 (see Table p. 404). 



The displacement of the neutral axis between the loads of 

 8000 and 16,000 lb. is here "178 inch. 



Another series of measurements given by Mr. Barlow of 

 the same beam inverted but with similar loading is valueless 

 for the purpose of comparison, inasmuch as the measured 

 lengths as loaded are compared with those taken before the 

 inversion of the beam, and are therefore affected by its own 

 weight in the opposite direction, and also affected by the con- 

 siderable internal stresses caused by the overstrain to which 

 the beam had already been subjected. 



The amounts of displacement of the neutral axis may not 

 appear considerable, but it must be remembered that within 

 the limits of elasticity, and so long as the calculated stress at 

 the lower side of the section does not exceed the direct tensile 

 strength, all the facts are explicable upon the ordinary theory 

 with the neutral axis in the centre ; and it will be hereafter 

 seen that for beams of rectangular section, even with extreme 

 loads, no greater displacement is to be expected until the 

 breaking weight is nearly reached, the utmost amount being 

 about one tenth of the depth of the beam, or in this case about 

 two thirds of an inch. 



Another circumstance to be remarked in these experiments, 

 and likewise in the other experiments made by Mr. Barlow 

 hereafter to be referred to, but which does not appear to have 

 been noticed by him, is that the elongations and contractions 

 and the deflexions resulting from loading increase, not in the 

 ratio of the load, but in a higher and increasing ratio. 



Thus, for the 1st Beam, with a load of 

 5,786 lb. the maximum elongation ayhs '000b\33 or -000105) per 1000 lb. 

 10,260 „ „ -00120 „ -000117 ., „ 



14,746 „ „ -00U)6 „ 000183 „ 



