654 thp: inventors of the telegraph and telephone. 



l)robleni!S weir of a nioie])urelyscientilif character than those preseiiteil 

 in. the developments which had been in progress, and consecpiently 

 tested the knowledge then existing- of the laws of electricity uinch more 

 severely. It was very soon discovered, for example, that the rate at 

 which signals conld be transmitted, and the l)attery power or other 

 electro-motive force necessary to effect the transmission, did not, as in 

 land lines, depend almost entirely on the size and length of the con- 

 ductors used. The electrostatic capacity of the line immediately began 

 to play an important ])art, and signals were found not to be transmitted 

 so instantaneously as they were on existing- land lines. Again, there 

 was no opportunity- of using' relays, so as to effectively shorten the lon- 

 o-er lines, and the investigations of Thomson led him to point out that 

 the rate of signalling- would be inversely as the square of the length. 



Such difficulties as these, cond^incd with the very evident difficulties 

 involved in manufacturing and submerging a cable in deep water, were, 

 to say the least, discouraging. Experiments on short lengths in the 

 English channel and elsewiiere proving successful, faith in the possi- 

 bility of longer cables grew, and very soon, through the enterprise of a 

 few American and English business and scientific men, an attempt was 

 made to hiy a cable across the Atlantic. The history of that undertak- 

 ing and its various failures are almost common knowledge, but perse- 

 verance concpiered all the diflfi<'ulties, and to-day no one thinks of the 

 probability of failuie wiien a long cable is proposed. 



The laying of long cables brought out the fact that, as had been an- 

 ticipated, existing telegraphic apparatus was not of great enough sensi- 

 bility to render moderately rapid signaling possible. This difficulty 

 was almost immediately met by the mirror galvanoscopic receiver of 

 Thomson, followed some years later by his siplion recorder, which is 

 undoubtedly by far the most sensiti\e recording telegraph known. 

 Improved methods of working cables soon followed, among which, in 

 the early days, probably the most notable is the introduction of con- 

 densers between the ends of the cable and the earth by Varley. The 

 successful duplexing of cables )>y :\luirhead has already been referred 

 to, but it is somewhat curious to note that although the electricians 

 interested in (;able working were familiar, as early as 185«>. and per- 

 liaps earlier, with tiie difficulty which had prevented siTccess on land 

 lines, no one seems to have thought of ai»plying the remedy. As early 

 as IS.IS, a ])atent was taken out by Thomson, in Avhich he proposed to 

 overcome the difhculity of (hiplexing <i cable by a. mechanical arrange- 

 ment for varying the compensating currents at the same rate that tlie 

 signaling current varies, lie lias since said that he did not propose 

 the use of condensers, be<'ause a means of producing a sufficiently good 

 model cable was not then known. Such a model cable was not avail- 

 aide for nearly twenty years alter the above date, and was finally })ro- 

 duccd by making pra<'ti<'iilly a copy of the actual cable, using tinfoil 



