1909] on Modern Suhmarine Telegraphy. 527 



At the instant that we start forcing the water in, practically none 

 escapes at the receiving end, the pipe commences to stretch and the 

 water begins to flow out, continuously increasing in quantity, until 

 it obtains a steady value : this steady value is reached when the pipe 

 has ceased to expand. 



The time taken for the pipe to expand and for the water to reach 

 a steady value is termed the variable period. The less the elasticity 

 of the pipe and the less the resistance to w^ater flowing through it, 

 the less the time taken to reach the steady value. 



This is equivalent to our submarine cable, where the less the 

 capacity and the less the resistance, the less the time constant, or the 

 quicker the rate of signalling. 



Now^ the swelling of the pipe or the capacity effect of the cable 

 does not destroy the energy in the water or of the electricity respect- 

 ively ; this is very different from the waste of energy through 

 resistance, and if by some method we could compensate for the 

 capacity we could signal through the conductor at any rate we liked, 

 being limited only by the strength of our battery and the sensitive- 

 ness of our receiver. 



I may say that the current usually received would be 1000 times 

 greater if we had no capacity but only the resistance to deal with.* 



As before stated, the cable has resistance : the current therefore 

 suffers attenuation. It also possesses capacity : the signalling currents 

 through it therefore suffer distortion. 



Before dealing with this distortion, I must refer you to the 

 diagram of the signals as they are sent into the cable (Fig. 5) and 

 received from it on the siphon recorder. 



You will notice that the signals, arranged to form the alphabet 

 in the cable code, are of varying lengths, being 1, 2, 3, 4 and 5 

 times the length of the individual or shortest signal. 



Sending and receiving on this principle is electrically equivalent 

 to working the cable with varying electrical frequencies of 6, 3, 2, 

 etc., complete periods per second. 



The lower the frequency the less the capacity affects the current, 

 so that the higher frequencies of 6 and 3 a second are more attenu- 

 ated than those of 2 and less. The signals that form the letters in 

 the alphabet are differentially attenuated, the quicker signals, such 

 as those forming a C, are much weaker when they arrive to operate 

 the receiving instrument than the slower signals that form the 

 letters M, 0, and so on for the other and longer signals. 



Submarine cable signalhng of the present day affords us with an 



* I must here refer to the fact that Mr. Heaviside twenty years ago showed 

 that by giving series inductance to a cable we could greatly increase our 

 rapidity of signalling. 



This will be understood from Table I. and Figs. 3 and 4 showing curves. 



Unfortunately we see no practical method of carrying out Mr. Heaviside's 

 suggestion, so that I must go on speaking of the submarine cable as it really is. 



