FUNDAMENTALS OF TELETYPEWRITERS 631 



when a distant station wishes to send a message, a signal may be sent 

 which will automatically start the motor and condition the receiving 

 machine so that it will properly record the message and then have its 

 motor automatically stopped again at the end of the communication. 

 Various devices are available for this purpose, some operating over 

 the regular signaling circuit and others requiring a separate circuit. 

 Similarly, in the case of TWX service, stations may, if desired, be 

 equipped for unattended service so that, if the station is called and no 

 attendant is present, the teletypewriter motor may be started remotely 

 by the switchboard operator and the station conditioned to record the 

 incoming message at the termination of which the motor can again be 

 stopped by the switchboard operator. 



Signal bells are usually provided on the machines so that, if it is 

 desired to call an attendant to a working machine or to call attention 

 to a specially important message being received, the bell can be rung 

 by signals sent over the circuit. 



A general feature incorporated in the design of all modern machines, 

 and one which is not often appreciated, is the so-called "overlap." 

 This feature makes high speed possible by overlapping the selecting 

 and printing parts of the receiving operation. In other words it 

 provides for the typing of one character to take place simultaneously 

 with the reception of the selecting impulses for the next character. 



Features of Page Teletypewriters 



Page teletypewriters have been built in several different forms, 

 notably with a moving paper carriage or a stationary paper carriage and 

 with a typewheel or with type bars for printing. An early design 

 employed a moving paper carriage and a typewheel, with an ink roller 

 for inking the characters on the wheel. With this design it was im- 

 practical to make satisfactory carbon copies, the printed record 

 was unevenly inked, and much trouble was experienced due to side 

 printing, that is, unwanted printing of portions of letters adjacent to 

 the desired letter on the typewheel. Furthermore, considerable 

 trouble was had in properly feeding paper from a paper roll through the 

 moving paper carriage. 



To eliminate these limitations and troubles it was decided that for 

 general service in the Bell System a new machine should be designed to 

 be capable of making as many carbon copies as a typewriter and that 

 it should use type bars and have a stationary paper carriage. This 

 sort of machine was new in the art and required extensive development 

 work to produce a satisfactory commercial design because of the in- 



