484 . Boy a I Society ; — 



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 

 maintained at that strength between the signals, the confusion of 

 interference would be avoided. He considered that, if the second or 

 earth-contact of each signal bore a fit proportion to the first contact, 

 this object might be effected ; and he considered that a succession of 

 very short pairs of contacts of a certain relative length, would main- 

 tain the current at the constant final strength during any pause sepa- 

 rating signals. He therefore prepared a paper band with openings cut 

 so as to make pairs of equal battery- and earth- contacts for dots, long 

 battery-contacts, followed by nearly equal earth-contacts, for a dash, 

 and a succession of pairs of very short contacts wherever a pause was 

 required, the battery contacts being rather the shorter of the two. 



The success of this plan was such that the signals were distinctly 

 recorded, not only by the galvanometer, but by a relay when the total 

 variations caused by the shortest signals were invisible on the galvano- 

 meter, i. e. even less than 1 per cent, of the maximum final current. 



7. Hence it was concluded that by the means adopted, or by 

 analogous means, " signals can be sent without confusion at any 

 speed which will allow the shortest signal used to cause a sensible 

 variation in the received current." 



These experiments were tried on dry cable coiled in iron tanks, and 

 might therefore not be applicable to extended and submerged cables. 



The author has, however, proved that the retardation and insula- 

 tion of an iron-covered cable are very little affected by the mere pre- 

 sence or absence of water ; and wherever the conclusions obtained 

 from the experiments agree with the deductions of theory, it is clear 



