480 
ME. W. H. BAELOW OX THE EESISTAXCE OF FLEXTEE 
tuted, as for example crystalline substances, yet great variation may be expected to 
occur between crystalline and malleable and fibrous substances. 
The only other point to be referred to is, as to the limit of action of the resistance of 
flexure. It appears evident that in all the simple sohd sections, the points of action of 
the resistance of flexure are the centres of gravity of the half-section ; while in the com- 
pound sections it is necessary to compute the centre rib and flanges as for two separate 
beams in which the resistance of flexure is different, and has its point of action at the 
centre of gravity of the separate portions. 
It would appear that the elastic reaction developes this resistance to the full extent, 
when the section is such that a straight line may be drawn from ever}’ point at the 
outer portion to every point at the neutral axis within the section ; but that if the form 
of section is such that straight lines drawn from the outer fibres, or particles, to the 
neutral axis fall without the section (as in the case in the compound sections, Xos. 15 
and 16), then it must be treated as two separate beams, each ha^-ing that amoimt of 
resistance of flexure due to the depth of the metal contained in it. 
Resistance of Flexure in Wrought Iron. 
Although from the fact, that in a cast-iron beam (the section being a solid rectangle) 
the neutral axis was found to be at the centre of gra'\ity of the section, it might have 
been inferred that the same would be found in wrought iron ; yet it was considered 
desirable to ascertain it by actual measurement. For this purpose two beams were 
taken, one of rolled iron, 7 feet 6 inches long, 6 inches in depth, and 1|- inch in breadth ; 
the other of hammered iron, 8 feet long, inches in depth, and If inch in breadth. 
Holes were drilled at about 6 inches on each side of the centre, or point of application 
of the strain, for the insertion of the pins of the measuring instrument. The holes were 
six in number, and placed at equal distances from the upper to the lower side of the 
beam ; and the experiments were conducted in the same manner as those made T^ith the 
cast-iron beam, and described in my former paper. 
Experiment for Determination of Neutral Axis. 
Wrought Iron Beam (rolled iron). 
Depth 5’ 93 inches. 
Breadth 1-28 inch. 
Length of bearing . . 60 inches. 
Beam without 
weight. 
Difference. 
Weight applied 
at centre, 
7840 lbs. 
Difference. 
Weight applied 
at centre, 
11,200 lbs. 
DifiFerence. 
Weight 
taken off. 
Permanent 
set. 
Micrometer 
Micrometer 
Micrometer 
Micrometer 
readings. 
readings. 
readings. 
readings. 
1741 
+ 25 
1766 
+ 13 
1779 
-38 
1741 
i 1769 
+ 14 
1783 
+ 7 
1790 
-22 
1768 
— 1 
1633 
+ 5 
1658 
+ 5 
1663 
-10 
1658 
1787 
— 5 
1782 
+ 2 
1784 
+ 2 
1786 
— 1 
1706 
-12 
1694 
— 8 
1686 
+ 22 
1708 
+ 2 
1746 
-23 
1723 
— 11 
1712 
+ 38 
1750 
+ 4 
