94 



Professor J. A. Fleming 



[March 27, 



on long cables would preserve the necessary wave amplitude that 

 perhaps hindered its trial on a large scale. 



Mr. Oliver Heaviside had, however, pointed out in 1887 that the 

 wave distortion in cables could be cured bv giving to the cable 

 increased inductance ; and he proved mathematically that if the four 

 line constants of the cable per mile were so adjusted as to magnitude 

 that the product of the line inductance and insulator conductance 

 was equal to tlie product of line resistance and capacity, then this 

 cable would possess the peculiar property that vibrations or electric 



Fig. 3. — Distortion of Vowel Sound " 00 " by Transmission 

 ALONG 30 Miles of Standard Telephone Cable. 



The upper curve shows the wave form of the current at the 



sending end, and the lower curve the distorted form at the 



receiving end of the cable,^ 



waves of all wave lengths would travel along it with equal speed and 

 be attenuated at an equal rate or in equal proportions. 



Hence such a cable would allow a wave form to be propagated 

 along it without distortion. 



In all ordinary cables the product of the line resistance and line 

 capacity is too large to fulfil Heaviside's condition, and hence we 

 must give the cable greater inductance to bring about an approxi- 

 mation to the distortionless condition. 



This addition of inductance is called loading the cable. 



Heaviside merely gave a general instruction that loading would be 

 beneficial, but the exact details how to do it were left to be discovered. 



