ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 271 



the line. The effect of these inductance coils is to permit of the 

 satisfying of equation (79) (magnetic energy equal to electric 

 energy) with a very greatly reduced value of current in the line 

 wires so that the RI Z loss, which is the cause of the wave dis- 

 tortion, is very greatly reduced. A telephone line provided with 

 inductance coils in this way is called a loaded line. This arrange- 

 ment is due to Pupin. 



The canal analogue of a loaded telephone line is as follows : 

 Imagine a great number of thin boards to be placed across the 

 canal in the form of diaphragms but free to move with the water 

 in the canal, and imagine these thin boards to be very massive. 

 The effect of these massive boards would be to reduce the 

 velocity v in Fig. 1 90 and still permit the kinetic energy of the 

 moving water and boards to be equal to the potential energy due 

 to the elevation of the water in the wave. This reduced velocity 

 of flow v would greatly reduce the friction of the water against 

 the sides of the canal and therefore the kinetic energy of the 

 wave would be dissipated much less rapidly than if the water in 

 the canal were not loaded. 



The loading of a telephone line is helpful only when the energy 

 loss due to line resistance is much greater than the energy loss 

 due to line leakage (poor insulation). When line leakage (poor 

 insulation) is excessive, the loading of the line tends to increase 

 wave distortion. The explanation of this effect of loading is as 

 follows : The velocity of transmission of the waves along a line 

 is greatly reduced by loading so that a longer time is required 

 for a wave to travel over the line and therefore the wave-loses 

 energy by leakage for a longer time.* 



PROBLEMS. 



143. Ten horse-power is transmitted along a row of gear wheels, 

 the speed of each of which is 1,200 revolutions per minute. The 



* The student who wishes to pursue the study of the theory of electric waves 

 should read Heaviside's Electromagnetic Theory, Vols. I and II, London, The Elec- 

 trician Company. The second part of Vol. I, namely, pages 306 to 455, is especially 

 instructive. 



