MATERIALS, STIIE3TG-Til OF. The , strength of any Material object, as a rod, bar, I beam, Chain, of 'rope, is that Power by which the substance resists an 'effort to destroy the cohesion of its parts, If it red or bar be sus pended vertically, and it •eight fixed to the lower end, that weight would tear asunder the bar, fibre from fibre, or particle frotri particle, if increased beyond a Certain limit. Supposing the bar to be one inch square, the following weighti would suffice to tear it asunder, ac cording to the material of Which it is made:— English oak . . 8,060 to 12,000 lbs.
Fir 11 000 to 13,188 lbs.
Beech . . . . 11,500 Mahogany . . 8,000 Teak 15,000 Cast•steel . . I81,25d • Iron-wire . . 93,064 Swedish bar-iron 72,091 Cast-iron . . 18,056 to 10,488 lbs.
Wrought-copper 33,792 Platinum-wire . 52,987 Silver do. . . 38,257 Gold do. . 30,888 Zinc do. . 22,551 ' Tin do. . 7,129 Lead do. . 3,119 Rope, line, and cables range front 5000 to 12,000, according to the material and the mode of twisting.
According to the experiments of Mr. Bar low it appears that a bar of malleable iron is extended one ten-thousandth part of its length by a direct strain equal to one ton for each square inch in the area of the transverse sec tion : when stretched with ten tons per inch its elasticity was injured, or the bar did not return to its original state.
In relation to the power of bearing a crushing presSiire; vationg thateriali have been found to take rank as fdllowa :—Iton, granite, lime sterie, oak; Portland stone, white deal, elm, fed brick, and chalk.
Shied the strengths of beams attached at one end br Supported On props, the other climehaitinS being the Sitind, vary as the Squares of the vertical depths, it follows that the most AdrantageOns position, when the areas of the transverse Sections are equal, is that iii which the broadest surface is in a ver tical tiositioti. In this manner girders and
joists in edifices are iiWariably placed.
When a beam bi bar is attached at one end to a wall, or when it turns upon its middle point like the great lever of a steam-engine, if it be required that the Mini should be equally Strong in its whole length; it should be made to taper towards its extheinities. If a weight be applied at any point in the Width of a beam which is Sithiarted on two propS; the strain produced by it will be the greatest when it is placed in the middle.
Stich machines as capstans and witullasSes, also axles which revolve with their Wheels; are, when in action, subject to be twisted; so that their fibres thud to becfinie chrved in Ob lique directions : the Strain thus prodtleed is called that of torsion, and the strength of a solid cylinder to resist thiS kind of strain 'A found to be proPortional to the tube of the diameter. Since the Strain Cif tax-Sion depends on the cliaineter of the cylinder, it is evidebt that a hollow cylinder must be stronger than a solid one containing the same amount of material.
We May remark that in testing the stability bf the Palace of Industry in Hyde Park, a number of ingenious contrivances have been eiriployed; to determine the strength of the Materials to render the Serviect required of them; especially in respect to the columns and girders.