104 Professor J. A. Fleming [March 27, 



When such loaded cables are connected at their ends to land 

 lines which are not loaded there is a certain loss of amplitude by the 

 reflection which occurs at the junction where the two lines of 

 different impedance join. This effect is exactly similar to that which 

 occurs when a ray of light passes from one medium to another of 

 different refractive index. 



We can illustrate this phenomenon by use of our vibrating string. 

 If we put a single heavy bead in the centre of our string and vibrate 

 one end of it with the motor so as to make waves travel along it, 

 you see that strong waves exist on one half of the string but very 

 feeble ones on the other. When the waves meet the load they are 

 partly transmitted and partly reflected, just as when a ray of light 

 meets a sheet of glass. (See II, Fig. 1.) 



If we put several beads upon the string at distances comparable 

 with the half wave-length, then reflection takes place at each bead 

 and the waves die away in amplitude very quickly. 



If, however, we put beads of different sizes, beginning with a 

 heavy bead in the centre and beads decreasing in mass on either 

 side of it so as to make a tapered load, then the wave started at one 

 end of the coil passes through the loads with much less loss l)y 

 reflection. 



The same thing happens in the case of the passage of a ray of 

 light from one medium to another of different refractive index. 



If the refractive index is graduated very evenly there will be 

 refraction of the wave but less reflection. 



We meet with identically the same phenomenon in the case of 

 coil loaded telephone cables. It is necessary to taper off the loading 

 by increased spacing or gradual reduction of the inductance of the 

 coils to reduce the losses by reflection when the waves pass from the 

 coil loaded cables to the unloaded terminal wires. 



Some interesting curves were uiven by Dr. Hammond Y. Hayes 

 in a paper before the Electrical Congress at St. Louis showing the 

 effect on the attenuation of a telephone line when not loaded, when 

 loaded, and when loaded with taper. These diagrams show well the 

 effect of tapering the loads in the increase of received current which 

 takes place. 



Of late years great attention has been paid by advanced tele- 

 phonists to the theory of the propagation of electric waves and 

 speech-currents along wires. We are no longer content with the 

 crude empirical rules which served the earlier telephonic engineers. 



Ohver Heaviside, Pupin, Kennelly, Campbell, Breisig and others 

 have provided the mathematical tools for practical workers to 

 use, and the predetermination of the results of any given cable 

 construction is now a matter of definite calculation, and not, as of 

 old, mere guess-work. When the attenuation constant of a cable is 

 known, the product of the constant and the length in miles of the 

 cable gives us a number called the total attenuation. Intelligible 



