FLEXIBILITY; FLEXURE. Flexibility is a property of bodies by which they yield transversely, on the application of some power : this property is distinct from elasticity, as it does not necessarily follow that the bodies acted on recover their original figures when the power is removed. DIA.Txma.s, STRENGTH OF; ROPES.] In intimate connection with this subject is the flexure of columns, which has undergone much investigation since the prevalent use of iron for columns. The fibres of wooden pil lars are generally of serpentine forms, and they adhere together laterally, with compara tively a small force : hence, when such a pillar is compressed longitudinally by a weight, the latter acts obliquely on the fibres ; and thus a pillar of wood becomes bent sooner than one formed of the other materials.
The valuable series of experiments carried on by Mr. Hodgkinson, and of which a full account is given in the Philosophical Trans. actions for 1840, have thrown much light on the flexure and strength of columns. In these experiments the columns, which were placed in vertical positions, were of various lengths, from a few i uches to seven foot six inches, and all were subjected to pressures acting vertically ; some were cylindrical and others were rectangular prisms, and the for mer were either solid or hollow : in some cases the ends of the columns were planes perpendicular to the lengths, in order that the pressure might be diffused uniformly over those ends ; and, in the others, the ends were hemispherical, in order that the pressure might be transmitted almost wholly in the direction of the axis. From his experiments
Mr. Hodgkinson has obtained the following conclusions :—All the pillars whose lengths exceeded four times their diameters became bent before they broke ; and, when the pillars were of uniform dimensions, both ends being plane or both hemispherical, the greatest flexure was near the middle of the length, and the fracture was at that place ; but when one end was plane and the other hemispher ical, the fracture was at a distance from the rounded end equal to about one-third of the whole length. Pillars of cast-iron with plane ends, and having their lengths about thirty times their diameters, were broken by weights equal to one-third or one-fourth cf those which would crush them if they had been made short enough to be crushed without bending. In some of the experiments the cast-iron columns were formed with discs at their ends, the diameters of the discs being about twice as great as those of the columns ; and it was found that these sustained a greater pressure before breaking than the simple columns. When the columns were thicker in the middle than at either end, their strength was thereby increased, if compared with cylindrical co lumns, by about one-eighth. In the prismatic pillars, the flexure always took place in the direction of a diagonal.
In all such buildings as the Crystal Palace, where the entire weight is supported on iron columns,the due appreciation of these various properties of columns is of the highest degree of importance.