10 EEPORT— 1882. 



adjunct the microphone, the names of Riess, Graham Bell, Edison, and 

 Hughes will ever be remembered. 



Considering the extreme delicacy of the currents working a telephone, 

 it is obvious that those caused by induction from neighbouring tele- 

 graphic line wires would seriously interfere with the former, and mar the 

 speech or other sounds produced through their action. To avoid such 

 interference the telephone wires if suspended in the air require to be 

 placed at some distance from telegraphic line wires, and to be supported 

 by separate posts. Another way of neutralising interference consists in 

 twisting two separately insulated telephone wires together, so as to form 

 a strand, and in using the two conductors as a metallic circuit to the 

 exclusion of the earth ; the working current will, in that case, receive 

 equal and opposite inductive influences, and will therefore remain un- 

 affected by them. On the other hand two insulated wires instead of one 

 are required for working one set of instruments ; and a serious increase 

 in the cost of installation is thus caiiscd. To avoid this Mr. Jacob 

 has lately suggested a plan of combining pairs of such metallic circuits 

 again into separate working pairs, and these again with other 

 workiflg pairs, whereby the total number of telephones capable of being 

 worked without interference is made to equal the total number of 

 single wires em^sloyed. The working of telephones and telegraphs in 

 metallic circuit has the fui'ther advantage that mutual volta induction 

 between the outgoing and returning currents favours the transit, and 

 neutralises on the other hand the retarding influence caused by change in 

 underground or submarine conductors. These conditions are particularly 

 favourable to underground line wii'cs, which possess other important 

 advantages over the still prevailing overground sj'stem, in that they 

 are unaffected by atmospheric electricity, or by snowstorms and heavy 

 gales, which at not very rare intervals of time put us back to pre- 

 telegraphic days, when the letter-carrier was our swiftest messenger. 



The underground system of telegraphs, first introduced into Germany 

 by Werner Siemens in the years 1847-48, had to yield for a time to the 

 overground system owing to technical difficulties ; but it has been again 

 resorted to within the last four years, and multiple land cables of solid 

 construction now connect all the important towns of that country. The 

 first cost of such a system is no doubt considerable (being about 38L per 

 kilometre of conductor as against 81. 10s. the cost of land lines) ; but as 

 the underground wires are exempt from frequent repairs and renewals, 

 and as they insui-e continuity of service, they are decidedly the cheaper 

 and better in the end. The experience aff"orded by the early introduction 

 of the underground system in Germany was not, however, without its 

 beneficial results, as it brought to light the phenomena of lateral 

 induction, and of faults in the insulating coating, matters which had to be 

 understood before submarine telegraphy could be attempted with any 

 reasonable prospect of success. 



Regarding the transmission of power to a distance the electric current 



