ON SOME MARVELS IN TELEGRAPHY. 251 



its full strength and as gradually subsides, the artificial 

 current must do the same. Reverting to the illustration 

 derived from the flow of water, if we had a small pipe the 

 rapid flow through which was to carry as much water one 

 way as the slow flow through a large pipe was to carry water 

 the other way, then if the large pipe had a widening along 

 one part of its long course the short pipe would require 

 to have a similar widening along the corresponding part of 

 its short course. And to make the illustration perfect, the 

 widenings along the large pipe should be unequal in different 

 parts of the pipe's length; for the capacity of a submarine 

 cable, regarded as a condenser, is different along different 

 parts of its length. What is wanted, then, for a satisfactory 

 system of duplex telegraphy in the case of submarine cables, 

 is an artificial circuit which shall not only correspond as 

 a whole to the long circuit, but fhall reproduce at the 

 corresponding parts of its own length all the varieties of 

 capacity existing along various parts of the length of the 

 submarine cable. 



Several attempts have been made by electricians to 

 accomplish this result Let it be noticed that two points 

 have to be considered : the intensity of the current's action, 

 which depends on the resistance it has to overcome in 

 traversing the circuit ; and the velocity of transmission, de- 

 pending on the capacity of various parts of the circuit to 

 condense or collect electricity. Varley, Stearn, and others 

 have endeavoured by various combinations of condensers 

 with resistance coils to meet these two requisites. But the 

 action of artificial circuits thus arranged was not sufficiently 

 uniform. Recently Mr. J. Muirhead, jun., has met the 

 difficulty in the following way (I follow partially the account 

 given in the Times of February 3, 1877, which the reader will 

 now have no difficulty in understanding) : He has formed 

 his second circuit by sheets of paper prepared with paraffin, 

 and having upon, one side a strip of tinfoil, wound to and 

 fro to represent resistance. Through this the artificial 

 current is conducted. On the other side is a sheet of tin- 



