THEORETICAL & EXPERIMENTAL RESEARCH On the force of torsion, and on the elasticity of metal wires

This translation of Coulomb's memoir on the theory governing the torsional behavior of wires and the experimental determination of how the torsional stiffness depends on wire radius and length was made for a course taught by Louis Bucciarelli and Jed Buchwald at MIT (circa 2000) in which students attempted to replicate historic experiments using only the devices and materials available at the time of the original tests. The knowledge Coulomb acquired in his investigation of the elastic behavior of filaments of metal served, in subsequent memoirs, as a basis for the construction and use of balances to study the interaction of electrically charged bodies and of magnetized needles. The translation is followed by an outline and notes on Coulomb's theoretical analysis.This Memoir has two objectives: the first, to determine the elastic force of torsion of fil-aments of steel and of brass as a function of their length, their thickness, and their degree of tension. I have already had need, in a Memoir on magnetized needles printed in the ninth volume of Savans Etrangers, to determine the force of torsion of hair and of silk; but I have never occupied myself with filaments of metal, because the nature of my research led me to choose the most flexible suspensions for the same force, and I have found that the filaments of silk had incomparably more flexibility than filaments of metal. The second objective of this Memoir is to evaluate the imperfection of the elastic reaction [inelastic behavior] of filaments of metal, and to examine the consequences that one can deduce about the laws of coherence and elasticity of bodies