ARTICLES BY BELL SYSTEM AUTHORS 481 



Number 5 Crossbar Dial Telephone Switching System* F. A. Korn^ and 

 James G. Ferguson.^ A.LE.E., Trans., v. 69, pt. 1, pp. 244-254, 1950. 



Abstract — The field of application of this new switching system is more 

 extensive than that of any developed previously. The Number 5 system is 

 capable of operating with all present local, tandem, and toll switching sys- 

 tems of the Bell System and of the independent companies which connect 

 with it. In addition, it can serve as a tandem or toll center switching office 

 where this is advantageous. It can be readily equipped with features for 

 operation as required at toll centers for nationwide operator toll dialing and 

 also for automatic message accounting which permits subscriber dialing to 

 be extended to considerable distances. Number 5 crossbar is designed for 

 operation with as few as four digits in a subscriber number or it can complete 

 calls which require as many as 11 digits, (dialed by operators) three for the 

 national area code, three for the office code, four for the numericals and the 

 last for the station letter of the called number on certain types of party line 

 service. 



Carrier-Controlled Relay Servos * J. C. Lozier.^ Elec. Engg., v. 69, pp. 

 1052-1056, Dec, 1950. 



Abstract — A study of servo systems shows that, when properly designed, 

 the carrier-controlled relay servo will perform as well as a servo system with 

 proportional control. In this article the problem of designing a carrier- 

 controlled relay servo system for remotely tuning the variable capacitors of 

 a transmitter is analyzed. 



Quality Rating of Television Images * P. Mertz,^ A. D. Fowler,^ and 

 H. N. Christopher.1 I.R.E., Proc, v. 38, pp. 1269-1283, Nov., 1950. 



Abstract — Two methods of evaluating impairments in television images 

 are described. Both employ observers and, therefore, yield subjective evalua- 

 tions. The first is an extension of Baldwin's in which observers vote a prefer- 

 ence between pictures with different impairments; one of the pictures is 

 optically projected somewhat out of focus and is used as a reference. In the 

 second method, the impairment is rated by observers in terms of pre-worded 

 comments which are numbered and form a rating scale. Both methods permit 

 an evaluation in terms of liminal increments as computed from the distribu- 

 tion of votes of the observers. These methods have been used to evaluate the 

 impairing effects of echoes and noise in television pictures, and also to relate 

 picture sharpness to other quality parameters. 



Fundamentals of the Automatic Telephone Message Accounting System* 

 J. Meszar.i A.LE.E., Trans., v. 69, pt. 1, pp. 255-268, 1950. 



* A reprint of this article may be obtained on request to the editor of the B. S. T. J. 

 » B. T. L. 



