Determination of Limit of Proportionality of Wires

IN connexion with the determination of the limit of proportionality of cold-drawn wire, the following technique, which so far as we are aware is novel, has been used with success. The wire itself is employed as a'strain gauge', the increase of electrical resistance as the load is increased being measured. The electrical contacts near the grips of the tensile testing machine were connected to a Cambridge dial bridge on which the resistance was measured ; gauge-lengths of 50 or 100 cm. were employed.