OKLAHOMA ACADEMY OF SCIENCE 97 



length and a long length of wire, — middle portions of both lengths 

 at the same temperature — it was possible to get the angle of twist of 

 a section of the wire, all of which was at a uniform temperature. 

 The torque necessary to produce the twist in the heated wire was 

 measured by the twist in a fine cold tungsten wire of known con- 

 stants. The temperatures were measured by means of an optical 

 pyrometer of the Morse type; corrections were made for the absorp- 

 tion of the evacuated glass tube which enclosed the wire. 



The modulus of simple rigidity for a equiaxed wire was foimd 

 to be 21.7x1011 dynes per cm2 at 1000°K and only S.lxlQH dynes 

 per cm2 at 2000° K. There was a relatively smiall decrease in the 

 rigidity modulus between room temperatures and 1100°K. At a 

 temperature (1600°K) where the rigidity of the tungsten was 

 equal to that of steel at room temperature, the elastic limit of the 

 tungsten was, relatively, very small. 



Jeffries'* work on the change of crystal structure of tungsten 

 wire 1-W heat-treatments at various temperatures makes it possible 

 to dravv' the following conclusions from the temperature-rigidity 

 curves of the 10-mil tungsten wire. 



(1.) The rigidity of an equiaxed tungsten wire is greater than 

 that of a freshly drawn wire, both m.easurements being made at the 

 same temperature. 



(2.) Heat treatm.ent in the grain growth region causes an in- 

 crease of rigidity at temperatures between 300° and 2000° K, and 

 probably at all temperatures. Increase in the grain size causes an in- 

 crease in the rigidity modulus. 



Moduli of rigidity, as given in tables of physical constants, have, 

 in general, been obtained from angles of twist which were not 

 great enough to cause the elastic limit of the material to be passed. 

 In the writer's research, the angles of twist were less than 0.01 

 degree per centimeter length of wire, and yet, at the higher tem- 

 peratures, this was considerably beyond the elastic limit. The read- 

 ings of the angles of twist were made so quickly that the results 

 calculated from them were very similar to those which would have 

 been obtained if a torsion pendulum of very short period had been 

 used. It is suggested that the moduli of rigidity calculated from 

 such observations be called moduli of "Instantaneous Rigidity." 



*The Metallography of Tungsten, Trans. Am. Inst. Mining 

 Eng. pp. 1037-1052, 1918. 



