360 BELL SYSTEM TECHNICAL JOURNAL 



that, for any given class and length of pole, all six species are equal in 

 strength. In calculating these six-feet-from-butt sizes, distance from the 

 butt to the ground line for any given pole was assumed, by definition, to be 

 as shown in the column in the tables headed "Ground Line Distance from 

 Butt." The equality-in-strength principle holds good, however, for any 

 reasonable depth of set required. 



Approval of the six standards at this time followed a policy adopted by 

 the Standards Council of the American Standards Association in April 1939. 

 At that time the Standards Council decided to withdraw approval of stand- 

 ards having a tentative status, and requested the reconsideration of such 

 standards with the idea of either discarding them or of advancing them to 

 American Standards. 



Equilibrium Relations in the Solid State of the Iron-Cobalt System? W. C. 

 Ellis and E. S. Greiner. There are important transformations in the 

 solid in the iron-cobalt system. One of these originates from the A3 trans- 

 formation in iron. Cobalt in the binary system at first raises the A3 trans- 

 formation to a maximum in the region of 45 weight per cent cobalt. Fur- 

 ther additions decrease the temperature of transformation which rapidly 

 approaches room temperature in the region of 80 weight per cent cobalt. 

 An extended two phase region from 76.5 to 88.5 weight per cent cobalt was 

 established at 600 degrees Cent. (1110 degrees Fahr.). 



An order-disorder transition occurs in the alpha phase in the region of 50 

 weight per cent cobalt. The critical temperature of order is in the neighbor- 

 hood of 700 degrees Cent. (1290 degrees Fahr.) depending upon the com- 

 position. The ordered arrangement has the cesium chloride structure. 



The lattice constants of the alpha phase deviate widely from a linear 

 function of the cobalt content. The first additions of cobalt increase the 

 cell size to a maximum at approximately 20 per cent cobalt. Further addi- 

 tions result in a contraction in the cell size to the limit of the alpha phase. 

 Compositions in the region of 50 per cent cobalt exhibit an increase in cell 

 size on ordering. 



Determination of Microphone Performance.^ F. L. Hopper and F. F. 

 RoMANOW. Methods of determining the performance characteristics of 

 microphones by acoustic measurements are described. Work factors in- 

 volving the accuracy of the methods are discussed. The correlation be- 

 tween a microphone's performance as determined by acoustic measure- 

 ment and by listening tests is reported. Application of both types of test 

 to a studio type of cardioid microphone is given as an example. 



^ Trans. Amer. Soc. for Metals, June 1941. 



^ Jour. Soc. of Motion Picture Engineers, April 1941. 



