ON THE ELECTRICAL CURRENTS OF THE EARTH. 



By Charles Matteucci. 



TRANSLATED FOR THE SMITHSONIAN INSTITUTION. 



The study of electric currents in the terrestrial strata dates, I think, from the 

 discovery of the galvanometer. M. Fox, in England, was the first who saw the 

 needle deviate when different points of a metallic vein were touched with the 

 extremities of the wire of the galvanometer. M. Becquerel afterwards made very 

 extensive researches on electric currents obtained between masses of water and strata 

 of earth existing under different conditions. Till then these experiments were 

 regarded but as obscure cases of electro-chemical action, of difficult interpretation. 

 There was no thought, in this case, of any such thing as a ten-estrial phenomenon — 

 that is to say, of spontaneous electric cun'ents, as they are called by the celebrated 

 astronomer of Greenwich — until very strong electrical currents had been observed 

 in telegraphic wires daring the appearance of the aurora borealis. This phenome- 

 non presented itself for the first time, November 17, 1847, in the telegraphic wires 

 of Tuscany, while a bright aurora was visible on the horizon. The description 

 of this phenomenon, which I gave to the French Academy in a letter addressed 

 to M. Arago, was followed shortly afterwards by similar observations made 

 in the United States. In late years numerous observations have been made on 

 this subject on all telegraphic lines, and have confirmed the first results. It 

 was natural to seek the existence of electric currents and their laws in telegraphic 

 wires, independent of the simultaneous appearance of the aurora borealis, and 

 the Academy of Sciences is cognizant of the researches on this subject which 

 have been made public by such eminent savants as MM. Baumgarten, Barlow, 

 Lloyd, and AValker. When their memoirs are read with the attention they 

 merit, no one can fail to be struck with the difficulty which presents itself in 

 harmonizing the results they have obtained and deducing some general conse- 

 quence which might set us in the way of explaining these phenomena. All these 

 researches have been conducted by introducing a galvanometer into telegraphic 

 lines, and measuring the cun-ents at such times as the lines were not in service 

 for the transmission of despatches. Ordinary communications, established as 

 telegraphic stations between the metallic wires and the earth, are effected, we 

 know, in different ways ; sometimes they are fomied by plates of iron or copper 

 plunged into the water of wells more or less deep, and connected with the 

 metallic wires; sometimes these wires communicate with the shafts of pumps or 

 with the rails of an iron road. With the exception of the distinguished astronomer 

 of Munich, who seems, especially in his later experiments, to have duly con- 

 sidered the necessity of guarding against currents excited by the extremities of 

 the lines in communication with the earth, the observers have given us no inti- 

 mation how these communications were established. 



Yet it is not difficult to discover on anV telegraphic line taken at hazard that 

 the currents obtained in these lines depend on the heterogeneousness of the 

 plates which communicate with the earth. I have often seen these cm'rents 



20 S 



