ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 225 



developing a long tail, and the energy of the head of the wave 

 decreases, because of loss of energy in heating the wires, and also 

 because of the carrying away of energy by the long drawn out 

 ribbon wave which constitutes the tail. The state of affairs 

 after the original wave has traveled a short distance is shown 

 approximately in Fig. 160, the initial state of affairs being shown 

 in Fig. 159. The tail of the wave in Fig. 160 is traveling back- 

 wards as indicated, and the voltage in the tail is negative* as 

 represented by the curve W '. 



When a rectangular wave pulse enters a line of which the wire 

 resistance is negligible but which is poorly insulated, then the 

 effect is very similar to what is shown in Fig. 160. In this case 

 the electrical energy of the wave is reduced by line leakage and 

 the wave develops a tail. Wire resistance causes a rectangular 

 wave pulse to develop a tail in which voltage is reversed, and line 

 leakage causes a rectangular wave pulse to develop a tail in which 

 current is reversed. 



The effect of wave distortion is very serious in long distance 

 telephony. Thus the curve in Fig. 161 represents the com- 

 plicated wave which enters a telephone line from the transmitter 

 when the syllable high is spoken into the transmitter, and the 

 reproduction of the original sound by the distant telephone 

 receiver depends upon the delivery of this complicated wave 

 with all of its fine detail at the distant end of the line. The effect 

 of wire resistance (or the effect of poor insulation), however, is 

 to cause each shortest portion of this complicated wave to spread 

 over the line by the development of a tail as explained in con- 

 nection with Fig. 1 60. That is, a tail shoots out backwards from 

 each shortest portion of the wave in Fig. 161, and the result is 

 the smoothing down of the sharp points and the filling in of the 

 deep valleys of the curve so that all fineness of detail of the 

 original w r ave shape is obliterated and nothing but a dull droning 

 sound is produced in the distant telephone receiver. 



* The tail of the wave in Fig. 160 may be thought of as a pure wave at the very 

 beginning, but it soon becomes impure just as the head of the wave itself becomes 

 impure. 

 16 



