228 ADVANCED ELECTRICITY AND MAGNETISM. 



4. The rate of loss* of energy in the insulation is the same as 

 before. 



5. The time of transit of the wave is doubled. Therefore 



6. The actual loss* of energy in the wires is half as much as 

 before. 



7. The actual loss* of energy in the insulation is twice as much 

 as before. 



Therefore, to quadruple the inductance of a line halves the 

 wire loss of energy and doubles the leakage loss of energy for the 

 same amount of energy transmitted. 



The practical importance of loading of telephone lines grows 

 out of the fact that in any well built line the insulation is very 

 good so that the wire loss of energy is very much greater than the 

 leakage loss, and the loading of a line produces a two-fold im- 

 provement, namely, (a) the actual total loss of energy is reduced 

 and (b) wave distortion is greatly reduced by bringing wire loss 

 of energy and leakage loss of energy more nearly into equality 

 with each other. 



Remark. Pure wave transmission is markedly different from 

 ordinary power transmission in that there is a fixed relation be- 

 tween voltage and current in a pure wave as explained in Art. 

 1 1 6, and a more efficient transmission cannot be obtained by 

 increasing the voltage. 



124. Electrical oscillation of a transmission line. If a wave 

 (like Fig. 146, for example) is set up on a transmission line it 

 is repeatedly reflected at the ends of the line and made to travel 

 back and forth over the line, and the line is said to oscillate. 

 (a) If both ends of the line are open, the wave is reflected from 

 one end with reversal of current, and again reflected from the 

 other end with reversal of current, and thus the wave is brought 

 back to its initial condition. Therefore the line passes through 



* These energy losses are what are called first order approximations, inasmuch 

 as they are calculated on the assumption that E and / in the wave keep their 

 initial values during the entire transit of the wave from end to end of the line. 



