It is now very popular to apply the wire strain gage to the measurement of stress and strain in various cases for the reason of its convenience. But in the case of the rotating disc, it is necessary to contrive a special devise to pick up the change of electrical resistance of the gages, which are stuck on the face of the rotating disc.
In this paper, they first studied the variation of the contact resistance between the copper pole and mercury bath, and affirmed that the variation of the contact resistance between the copper pole and mercury bath is negligible small, if the immerged depth is adequate and this devise is adoptable. Having used the copper ring with the sharp edge as the pole, they could measure fairly well the strain of the rotating disc whose peripheral speed was about 300 meter per minute or less at the edge of the ring.
Applying this electric connecting devise, we have first measured the strains which were produced in a rotating circular disc of uniform thickness, secondly the disc having symmetrically placed four noncentral holes and finally the tangentially stepped circular disc.