IX. Account of experiments on the flexural and torsional rigidity of a glass rod, leading to the determination of the rigidity of glass

Abstract

These experiments were conducted in the Physical Laboratory of Glasgow University during the summer vacation of 1865, upon a plan devised by Professor W. Thomson, which may be briefly described as follows:— A cylindrical rod of glass is subjected to a bending couple of known moment, applied near its ends. The amount of bending produced in the central portion of the rod is measured by means of two mirrors, rigidly attached to the rod at distances of several diameters from each end, which form by reflexion upon a screen two images of a fine wire placed in front of a lamp-flame. The separation or approach of these two images, which takes place on applying the bending couple, serves to determine the amount of flexure. In like manner, when a twisting couple is applied, the separation or approach of the images serves to determine the amount of torsion.