The writer has at various times discussed the elastic properties of wires made by alloying different percentages of iridium with platinum. In particular this study has been carried on with a 40 per cent alloy. The principal feature of the previous work was a study of the torsional elastic properties of this wire; the wire in these cases being used as the suspension of various torsion pendulums. One of the facts of most importance developed in this investigation was that the period of the pendulum not only depended upon the amplitude (a fact discovered by Guthe) but that the relation of the period to the amplitude was not always a constant one. In fact in the earlier investigation it appeared that the connection between period and amplitude was such a complicated one, that any further study of the elastic properties must first be directed toward this one relation of period and amplitude. A good advance in this knowledge was recorded in the paper previously referred to, but much remains to be done. Its importance in the theory of elasticity can hardly be overestimated
