SOME RECENT DISCOVERIES CONCERNING THE BEHAVIOR 
OF PLATINUM-IRIDIUM WIRES. 
BY L. P. SIEG. 
• The remarkable elastic properties of a certain platinum-iridium wire 
containing 40 per cent of iridium were first announced by Gutlieb In 
his experiments the wire was used as the suspension of a torsion pendu- 
lum. Although the amplitudes of vibration were less than 50 degrees, 
a marked increase both in the period and in the logarithmic decrement 
accompanied the increase in the amplitude. Cylinders of equal mass 
but of different moments of inertia were suspended from the wire, set 
in vibration, and tiihed, but as a result of these experiments no change 
was observed in the logarithmic decrement-amplitude curves. This 
absence of any effect led to the supposition that the damping Avas pro- 
portional to the amplitude, and independent of the velocity. 
The study of the elastic properties of such wires Avas continued by 
Guthe and the writer" during the latter ‘part of 1908 and the early part 
of 1909. In that Avork, Avires containing different percentages of iri- 
dium Avere used. The apparatus Avas so constructed that much larger 
amxDlitudes could be obtained than Avere obtainable before. As a result 
of the use of the larger amplitudes, additional information concerning 
the relation of period and of logarithmic decrement to the amplitude 
Avere obtained. It Avas found that although both the period and the 
logarithmic decrement varied directly with the amplitude for small 
Amines of the amplitude, they did not continue to do so for larger values 
of amplitude. Th^e periods at these large amplitudes tended to become 
constant, and at the same time the logarithmic decrements reached a 
maximum, and then diminished. The peculiarities in the elastic be- 
havior of these AAures Avere found to increase as the percentage of iri- 
dium Avas increased. 
This present paper represents only one of tAAm interesting facts con- 
cerning the action of a 40 per cent platinum-iridium AAure, Avhich facts 
have developed from observations on the wire taken during the present 
year. To make the conditions perfectly clear it Avill be necessary to 
1. — K. E. Guthe, Proc. loAva Acad. Sci. 15, p. 147, 1908; Abs. in Phys. 
Rev. 26, p. 201, 1908. 
