1862.J 199 



Repeated dots, when represented graphically, give an even wavy line 

 with large amplitudes of oscillation for slow speeds or through short 

 lengths, but rapidly approaching a straight line as the speed of 

 transmission or the length of the cable was augmented. 



If the maximum permanent deflection caused by the battery be 

 called 100, dots sent at the rate of 15 per minute through 2192 

 knots of cable caused oscillations in the received current of 12*7 per 

 cent. ; and sent at the rate of 50 per minute, this caused an oscillation 

 of less than 1 per cent. 



4. From this it was concluded that "on all submarine cables 

 there is a limit to the number of signals which can be sent per mi- 

 nute, a limit which cannot be exceeded by any ingenious contrivance." 



If we continue to call the maximum deflection due to permanent 

 contact 1 00, the mean height of the current observed during dots is 

 below 50, on account of time lost between the two contacts while 

 moving the sending-key. 



When dashes or lines are sent, i. e. long contacts with the battery 

 followed by short earth-contacts, an even wavy line is obtained, the 

 mean height of which is above 50 ; and when dots and dashes are 

 combined, the curves representing the changes of the current become 

 very irregular, sometimes flying above 50, sometimes falling below 

 this line ; and when long pauses, or a succession of long battery-con- 

 tacts are introduced, the curves become hopelessly confused, especi- 

 ally at the higher speeds, so that the signals cannot be disentangled, 

 even when the change of current can be continually followed. From 

 this it is concluded that, 



5. "There is a wide margin between the limit set to the speed of 

 transmission by the gradual diminution of the received signals, and 

 that set by their interference." 



Reverse currents have been recommended as a means of accelerat- 

 ing the rate of speaking through submarine cables. Their effect was 

 tested ; the arrival- curves and signal-curves obtained by their use 

 differed in no way from those obtained by simple currents and earth- 

 contacts. Hence it was concluded that, 



6. " The use of reverse currents does not alter the limit set by the 

 gradual diminution of the received signals, nor that set by their in- 

 terference." 



It occurred to the author that, if by any means the current could 

 invariably after each signal be brought to one constant strength and 



p2 



