ON THE RECOVERY OF THE ELASTIC PROPERTIES OF A 

 PLATIi\IUI\I-IRIDIUI\I AVIRE. 



BY L. P. SIEG. 



The writer lias at various times discussed the elastic properties of 

 wires made by alloying different percentages of iridium with platimum. 

 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 compli- 

 cated 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 re- 

 ferred to. but much remains to be done. Its importance in the theory 

 of elasticity can hardly be overestimated. 



It appeared in previous work with the wire that the relation between 

 period and amplitude depended very largely on the amount of vibra- 

 tion which the wire had undergone previous to any one experiment. 

 For example if the initial amplitude were 100°, the period changed 

 by 3 per cent ; if the initial amplitude were 200°, the period changed 

 by 6 per cent; and if the initial amplitude were 600°, the period 

 changed by S^/o per cent — all of the above dying down to zero ampli- 

 tude. Howevei', if the wire had been vibrated for some time at a large 

 amplitude, then the percentage change in coming to rest from a smaller 

 amplitude was much larger tlian those mentioned above. In fact it 

 seemed that after the wire had been vibrated at large amplitude, it had 

 acquired a peculiar elastic condition which could only be removed by 

 annealing it at bright red heat. There was some little evidence that 



^L. P. Sieg Phys. Eev. 31, p. 421, 1910. 



=K. E. Guthe, these proceedings, 15, p. 147, 1908. 



