530 Mr. Sidney George Broivn [March 12, 



tbe slow than the quick signals ; at the same time it does absorb 

 some of the quick, and so far as that is concerned it is harmful ; it 

 diminishes distortion, but at the same time it adds to the attenua- 

 tion. 



Now " distortion " means something more than the differential 

 transmission of various electrical frequencies : it also means the 

 " phase relation " of the current to the voltage, and this " phase re- 

 lation " varies with the various frequencies, so you see that " distor- 

 tion " looked at from all sides is rather a complicated phenomenon. 



By " pliase relation " we mean the position of the current with 

 regard to the voltage producing it. 



To understand what "phase relation" means let us take the 

 analogy of a pendulum in motion : — 



The force keeping the pendulum swinging is a maximum at the 

 end of each swing, while the greatest velocity resulting from this 

 f oi-ce is at the middle of the swing ; obviously the times of greatest 



Fig. 5. 



speed and greatest force are not co-incident : the one is out of phase 

 with the other by what mathematicians would determine, in the case 

 of the pendulum, as 90° or a quarter period. 



Now the current leads the voltage at the sending end of the 

 cable by 45°. If a series condenser is introduced to diminish dis- 

 tortion, it still further increases the lead, and reduces the effective 

 power into the cable. The effective power can only be a maximum 

 when the current and voltage are exactly in step, or in other words, 

 when there is no " phase relation." 



A receiving condenser is also harmful for the same reason as a 

 sending condenser. 



By abohshing the sending condenser and replacing the receiving 

 one by a magnetic shunt placed across the suspended coil of the 

 siphon j^-ecorder or relay in 1898, the speed and accuracy of signal- 

 ling were materially increased. 



A magnetic shunt, as employed on the cables, consists of an 

 insulated copper wire wound round a closed circuited iron core. 



The resistance of the shunt is about 30 ohms : its inductance 



