Stress and Strain on the Properties of Matter. 526 



Matthey, and an analysis made by them of a similar specimen, not, 

 however, drawn into wire, yielded the results given below.* 





Proportion. 



Platinum -iridium at 10 per cent.. 



99 '33 

 0-23 

 0-18 



o-io 



0-06 











99-90 



The density at 0° C, calculated from this analysis, was 21*510, and 

 according to MM. Deville and Mascart the coefficient of thermal 

 expansion between 0° C. and 16° C. is 0-00002541. 



As it was not considered advisable to bend the wire so as to form it 

 into a coil suitable for finding the density in the ordinary way, the 

 latter was calculated from the mass, length, and diameter. The length 

 of the wire was 61*90 cm., the mass 22*088 grams, and the diameter, 

 us measured by the gauge at seven equidistant places, was as fol- 

 lows : — 



Number of 

 place. 



Diameter in centi- 

 metres. 



1 



-1454 



2 



0-1454 



3 



0-1453 



4 



1454 



5 



0-1453 



6 



0-1450 



7 



-1453 









0-1453 



From these data was deduced a density at 16° C. of 21*523, which 

 value, considering the drawing to which the metal had been subjected, 

 agrees very well with that calculated from the above analysis. 



The value of " Young's modulus " was first determined by the 

 static method in my usual way, and proved to be 2089 X 10 6 grams 

 per square centimetre, and though the length of the wire operated 

 upon was inconveniently small, the different trials agree very well 

 with each other. The modulus was next determined by the method of 

 longitudinal vibrations, the wire, which was sufficiently stout and rigid 



* " Nature," August 7, 1879, p. 343. 



2 m 2 



