& 



VOLUME XXIX APRIL, 1950 no. 2 



Kansas. City, jyio 



THE BELL SYSTEM 



TECHNICAL JOURNAL 



DEVOTED TO THE SCIENTIFIC AND ENGINEERING ASPECTS 

 OF ELECTRICAL COMMUNICATION 



Error Detecting and Error Correcting Codes 



R. W. Hamming 147 



Optical Properties and the Electro-optic and Photo- 

 elastic Effects in Crystals Expressed in Tensor 

 Form W. P. Mason 161 



Traveling-Wave Tubes [Second Installment] J. R. Pierce 189 



Factors Affecting Magnetic Quality R,M. Bozorth 251 



Technical Articles by Bell System Authors Not Appear- 

 ing in the Bell System Technical Journal 287 



Contributors to this Issue 294 



50^. Copyright, 1950 $1.50 



per copy American Telephone and Telegraph Company per Year 



