19U] on Improvements in Long-Distance Telephony' 91 



clear that slow vibrations or long waves of tension would be attenu- 

 ated more in travelling up such a strip than quick vibrations or 

 short waves. Such a quality of imperfect elasticity in the wire 

 could correspond to conductivity or leakance in the dielection of 

 a cable. 



Hence, we may sum up all our statements with regard to an 

 electric cable by saying that in virtue of its two energy-storing 

 qualities —viz. the inductance and capacity— we can have waves of 

 electric current or potential propagated along it just as we can have 

 waves of twist or displacement propagated along a steel strip or a 

 flexible thread. Also in consequence of its two energy-dissipating 

 powers of conductor resistance and dielectric leakance, these electric 

 waves along the cable are attenuated or weakened as they run 

 along it by reason of the gradual dissipation of the energy. 



We can quite easily show the production of stationary electric 

 waves on a wire by applying to the end of it a high frequency 

 alternating electromotive force, which in every way correspond to 

 the stationary waves we have produced on the string. 



If, however, we employ a straight wire the wave lengths are in 

 general so large that it is difficult to bring them with the space of a 

 room. We can, however, compress them by coiling the wire in a 

 close spiral round an ebonite rod. The high frequency electromotive 

 forces are created by connecting one end of this helix to some oscil- 

 latory electric circuit composed of a condenser, an inductive circuit, 

 and a spark gap. By adjusting this frequency to certain values we 

 can create stationary electric waves on the helix and the loops, and 

 nodes can be rendered visible by holding at various positions a neon 

 vacuum-tube, or by the electric glow on a fine wire stretched parallel 

 to the heKx. 



In the case of the helix here used in this experiment the velocity 

 of the electric waves along it is 1250 miles per second, and varies 

 inversely as the square root of the product of the capacity and 

 inductance of the helix per unit of length. We have, however, 

 little or no variation of velocity or attenuation of the waves with 

 wave length, because there is only very little dissipation of energy by 

 the resistance of the wire. 



I wish, however, to make evident to you that in an ordinary 

 submarine cable this is not the case. 



For this purpose I shall make use of an artificial cable constructed 

 on Dr. Muirhead's plan. In this apphance, the conductor, which 

 represents the wire of the cable, is a strip of tinfoil cut into a zigzag 

 shape and attached to a sheet of paraffined paper, whilst on the other 

 side of this paper is another complete sheet of tinfoil. This arrange- 

 ment has therefore capacity, resistance, and inductance like a real 

 cable. By employing a sufficient number of these sheets we can 

 imitate the electrical structure of any number of miles of submarine 

 cable. The artificial cable in front of me is equivalent to 100 miles 



