MEASUREMENT OF TELEGRAPH TRANSMISSION 163 



signal combination. Records of the distortion are made on message 

 registers in ranges of one per cent for small distortions and greater 

 ranges for larger distortions. 



As shown in Fig. 14, this device contains a sending distributor face 

 (a) to provide test signals and two receiving distributor faces {h) 

 and (c). Coupled to these and running five times as fast is a large 

 disc carrying a fine point from which a spark may be made to jump to 

 any one of a series of stationary segments. This is referred to as 

 "distortion-scanner" in the figure. Since the disc makes one-half 

 revolution while the sending distributor brush is traversing one seg- 

 ment, one-half revolution of the disc requires the same time as one 

 dot and is, therefore, equal to 100 per cent distortion. One hundred 

 segments are provided as indicated, each being equivalent to 1 per cent 

 distortion, so that this ring of segments forms a distortion scale 

 covering the range of ± 50 per cent distortion. Distortion indicators 

 are associated with these segments, each containing a gas-filled tube 

 and a message register. Only the first ten segments on either side of 

 zero are provided with individual indicating arrangements, the 

 succeeding segments being combined in successively larger groups as 

 shown in the figure; this affords adequate information for the usual 

 case. 



Assume the switches associated with the sending distributor face {a) 

 to be operated to send the signal shown in note 2a. After traversing 

 the circuit to be tested this signal operates the receiving relays, one 

 of which is associated with a "lag-meter" and the other with a spark- 

 producing circuit. If the time of occurrence of transition X (note 2-a) 

 is to be used as a reference, the MS switch of the lag circuit is closed 

 and the sending segments oriented until transition A" occurs while 

 the brush of receiving distributor {b) is midway between segments 9 

 and 10, as is indicated by a lag-meter reading of zero. The positions 

 of the segments of the receiving faces {b) and {c) with respect to the 

 signal will now be as indicated in notes 2-h and 2-c, and the set is 

 ready to measure the occurrence of a transition between any two 

 segments of the sending face, for instance, transition Y or Z. 



If for instance the displacement of transition Y with respect to 

 transition X is to be measured, the switch associated with face (c) is 

 set to connect to segment 4. When transition Y occurs the receiving 

 relays operate to marking, condenser C is discharged through the 

 primary of the induction coil and a spark jumps from the scanning 

 point to a stationary segment. If transition Y is not distorted the 

 spark will jump when the scanning point is opposite segment 0. 

 This will cause the gas tube associated with segment to fire and 



