526 



Mr. Sidney George Brown 



[March 12, 



The Ideal Core. (Fig. 2.) 



Diameter of core 



,, of copper 

 Resistance per nautical mile 

 Capacity .... 

 K.R. for 1852 nautical miles 



Fig. 2. — Ideal Gable. 



• 466 inch 



0-282 inch 



0-864 ohm 



• 700 microfarad 



2-06 



Speed of working with same duplex system ahout 240 letters per 

 minute, and the current received with this speed would be twice as 

 strong as in the actual cable, so that a still greater speed than that 

 given would result, perhaps a speed of 260 letters per minute, a 

 sending battery of 40 volts to be used on both cables. 



The copper conductor offers resistance to the electric currents 

 that flow along it ; this resistance by itself would, with sufficiently 

 sensitive receiving instruments, not affect the speed of signalHng : it 

 produces what is termed " attenuation " or a weakening of the 

 signalling current. 



There is also a lateral storage of electricity along the outside of 

 the copper due to the capacity of the insulating material to absorb a 

 charge of electricity ; this property is termed the electrostatic capacity 

 of the core. 



To allow this to be more fully understood, I shall take mechanical 

 analogies : — 



Resistance in electricity is equivalent to friction in mechanics, 

 capacity to elasticity of a spring, and self-induction to inertia. 



If I force water through an iron pipe, the friction in the pipe 

 offers resistance to the flow of water ; the same quantity that is forced 

 in, flows out at the receiving end, but the energy accompanying the 

 flow of water suffers attenuation, as part is wasted in overcoming the 

 frictional resistance. 



Suppose that, instead of taking an iron pipe, I take a soft india- 

 rubber pipe, a new kind of phenomenon will be noticed. As I force 

 the water in, the resistance that the water encounters in flowing 

 along the pipe causes the rubber to swell, and the rubber will 

 continue to swell until it has acquired sufficient strain to press with 

 sufficient force on the water to overcome the friction of the pipe. 



At the sending end, that is, the end where we are forcing in the 

 water, the pipe will swell the most, because the pressure on the water 

 is there the greatest, and the frictional resistance offered by tbe pipe 

 to its flow also the greatest. As we move along, the swelling will be 

 less, being least at the far end, that is, at the receiving end, where 

 the water escapes. 



