720 the bell system technical journal, july 1951 



Acknowledgments 



The writer gratefully acknowledges the valuable assistance rendered to 

 him in the preparation of this paper by Mr. H. S. Black, and the help of many 

 others who participated in the experiments and offered valuable comments 

 on the technical aspects of the analysis. These include: Messrs. C. B. Feld- 

 man, W. R. Bennett, J. O. Edson, and E. K. Van Tassel. 



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