TRANSATLANTIC TELEPHONING. 303 



It will be asked what this has to do with the transmission of speech 

 over long telephone lines. Speech is transmitted by electric waves, 

 and waves are waves, subject to similar laws, whether they occur in a 

 stretched cord, or in an elastic fluid, or in an electric current. From 

 energy transmitted by waves in a cord, to energy transmitted by 

 waxes in an electric current, is onty a step. It has long been known 

 that a conductor wound in a close coil gives to an electric current in 

 it something of the properties of a massive body. It is hard to start 

 a current in such a coil, l>ut once started, it is just as hard to stop it. 

 Coils placed along a telephone line will have an effect similar to the 

 masses along the cord. Electric waves started on such a line will be 

 persistent waves, they will not die out, they will retain their form 

 and characteristics. With such an aid the New Yorker can ask of his 

 Chicago correspondent, " What will that mine cost? " without fear that 

 he will understand it: "Who was that mean ?" 



But this is not the whole story. Let us go back to the weighted cord. 

 It is plain that a small motion, a comparatively slow movement, given 

 to the heavy masses would be the equivalent of a much more rapid 

 movement given to the cord alone. Slow movements always mean 

 small losses. The cost of carrying a ton from New York to Chicago 

 on a slowly moving freight train is far less than of carrying the same on 

 the high-speed passenger train. The slowly moving, heavily weighted 

 cord will carry from end to end the power imparted to it with little 

 loss in the resisting medium. 



So it is with the electric currents in Dr. Pupin's line. It is a heavily 

 weighted current. A very little current, with the high pressure it 

 can exert in consequence of the action of the coils, may convey as 

 much power as a much larger current on an ordinary line. Now, 

 every electrician knows that the loss of power occurring on a con- 

 ductor is proportional to the square of the current — that is, if you 

 have only half the current there is but one-fourth the loss; one-fourth 

 the current, one-sixteenth the loss, etc. Every electrician knows, too, 

 that the same power may be transmitted by a small current by increas- 

 ing the electric pressure just in proportion as the current is reduced. 

 This is recognized wherever electric transmission is employed. At 

 Niagara power is transmitted to near-by points at a pressure of 2,000 

 volts; but on the line to Buffalo 10,000 volts is employed, requiring 

 only one-fifth the current, and therefore one-twenty-fifth the loss if 

 the same conductors were used. In California, where power is to be 

 carried 150 miles, a pressure of 60,000 volts will be employed. Dr. 

 Pupin's line is another case of transmission by high pressure and small 

 current, and consequently small losses and little attenuation of the 

 waves. 



It has been said already that Dr. Pupin arrived at his results by 

 mathematical investigation. There was no haphazard experimenting, 



