OF ARTS AND SCIENCES. 61 



The theoretical possibility of teh^grnphing across large bodies of 

 water is evident from this survey vvljich I have undertakeu. The 

 practical possibility is another question. At no point in the survey 

 did I fiud an absence of earth currents. The peculiar crackling noises 

 heard in telephones are due to earth currents, and not to lluctuations 

 in the batteries employed on telephone circuits ; for they wei-e charac- 

 teristic of the circuits employed by me in which the earth was used as 

 a part of the circuit, and were absent when a battery circuit was 

 closed without the intervention of tlie earth. The tick produced iu 

 the exploring telephone whenever the circuit was closed through the 

 ground was due to earth currents, and not to polarization between tiie 

 copper wire and the wet earth ; for it was many hundred times stronger 

 than the polarization effects produced by dipping the copper tei'minals 

 of the telephone wire in acidulated water. This crackling noise pro- 

 duced by tlie earth currents in a telephone is a curious phenomenon, 

 and shows that the earth currents have a rapidly intermittent charac- 

 ter which escapes observation by any other instrument. A delicate 

 electro-dynamometer, for the registration and observation of these in- 

 termittent earth currents, is much to be desired. In some cases the 

 pulsatory effect of these earth currents was very marked. At no 

 point which I explored were evidences of earth currents absent. 



In a discussion of the earth as a conductor Steinheil says : " We 

 cannot conjure up gnomes at will, to convey our thoughts through the 

 earth. Nature has prevented this. The spreading of the galvanic 

 effect is proportional, not to the distance from the point of excitation, 

 but to the square of this distance ; at the distance of fifty meters only 

 exceedingly small effects can be produced by the most powerful elec- 

 trical effects at the point of excitation. Had we means which could 

 stand in the same relation to electricity that the eyes stand to light, 

 nothing would prevent our telegraphing through the earth without 

 telegraph conductors, but it is not probable that we shall ever attain 

 this end." * 



Theoretically, however, it is possible to-day to telegraph across the 

 Atlantic Ocean without a cable. Powerful dynamo-electric machines 

 could be placed at some point in Nova Scotia, having one end of their 

 circuit grounded near them and the other end grounded in Florida, 

 the conducting wire consisting of a wire of great conductivity, and 

 being carefully insulated from the earth except at the two grounds. 

 By exploring the coast of France, two points on two sui-faces not at 



* Dub. Anwendung des Elektromagnetismus, p. 172, 1873. 



