VII. Experimental determination of Poisson’s ratio

Abstract

The experiments with which this paper deals were carried out between the years 1883 and 1886 by Professor Kennedy and the author, with an instrument which the latter had originally designed for measuring local strains in metal structures, but which proved itself to be so exceedingly sensitive that it seemed capable of being applied to the measuring of the cross contraction of test pieces while these were subjected to a longitudinal pull, thus providing the means for measuring Poisson’s ratio direct. In its original form the instrument consisted of two small frames, which were secured to each other by means of two flat springs, in such a manner, that any relative motion was a perfectly parallel one. One of these frames carried a small piece of dark glass, and close to it, but on the other frame, a right-angled reflecting glass prism was secured.