308 ON THE ELECTRICAL CURRENTS OF THE EARTH 



G. By establishing communications between the lines south-east, south-west, 

 and north-east, north-west, the cuiTents realized were generally those which circu- 

 lated in tlie portion of the line pertaining to the south-north line. 



7. Only the temperature more or less elevated, which varied from 0° at night 

 to + ^^° t*i' 20° by day, was ever observed; the humidity or dryness of the air, 

 and even stormy weather, had an influence on the dh'ection and intensity of the 

 current of the meridian line. 



8. The results have been the same, whether the metallic portion of the line 

 was suspended on posts or laid upon the surface of the ground. 



What is the origin of these cun-ents? I believe it impossible to answer this 

 question with any confidence. What ought to be considered as perfecth' proved 

 by experiment is, that in a wire, when it reaches a certain length and its extrem- 

 ities are in good connnunication with the earth, there is an electric current which 

 constantly circulates, and principally in the direction of the magnetic meridian ; 

 the origin of this current is neither in the metallic part of the circuit, nor in the 

 terminal metallic plates, nor in any chemical action which might be surmised 

 betW'Cen the teri'estrial strata and these plates, or the liquids in which they are 

 immersed. 



Should these currents be considered as derived currents'? I have heretofore 

 demonstrated, what every one at present admits, and which is accordant with 

 theor}', that the resistance of a terrestrial stratum is very nearly null and does 

 not vary with the length of that stratum. These considerations are not favor- 

 able to the idea that the cuiTents we have described are derived currents. On 

 the plain of Saint Maurice, I have made some experiments to ascertain to what 

 distance from the electrodes of the battery derived cuiTents were sensible. I 

 used for extremities of the derived circuit the same plates of zinc plunged in the 

 saturated solution of the sulphate of zinc which have been described aV)ove. The 

 circuit of the pile was six kilometres in length ; its extremities consisted of square 

 ])lates of copper, 20 centimetres to the side, immersed in w-ater to the dc})lh of t\\o 

 metres. The batter}^ was composed of 20 elements of Daniell; the galvano- 

 meter of the derived circuit was that of 1,500 coils, before mentioned. When 

 each of the electrodes of the derived circuit was at a distance of 10 metres from 

 the electrodes of the battery, in a straight line l)etween tliese electrodes, I obtained 

 a steady derived current of 33° ; this deviation remained constant during the 

 whole time that the current of the battery did not vary, that is for several hours. 

 On increasing, to 50 metres, the distance bctw-een the electrodes of the battery 

 and those of the derived circuit, there were 4° of derived current; at 100 metres 

 this deviation w'as barely half a degree; and at a distance of 200 metres, it is 

 doubtful whether there was any movement at all in the galvanometer at the 

 closing of the circuit of the battery. It seems to me difHcult to derive from these 

 experiments any satisfactoiy reply as to the nature of the electric cuiTents observed 

 in long mixed lines. 



General Sabine, tlie highest authority of the present day in point of terrestrial 

 magnetism, appears to admit absolutely the magnetic iniiuence of the sun upon 

 the earth. But, if this iniiuence be admitted, what explanation can be given of 

 the currents we obtained and the differences of those currents according as the 

 line is in the meridian or perpendicular to it, or the periods of intensity in the 

 former of these lines? Assuredly these currents cannot be cuiTcnts of induction 

 due to the rotation of the earth. It is stated that Father Secchi, the indefati- 

 gable astronomer of Rt>me, is occupied at this time in investigating the connec- 

 tion which exists between the electric currents of long mixed lines and the vari- 

 ations observed in the instruments which measure the magnetic force of the earth. 

 If a connection of this kind were well established, we should certainly have taken 

 a step towards the interpretation of the electric phenomena of the earth. 



It remains to report a result which has some importance, and which I have 

 constantly realized: These terrestrial currents have a greater intensity, in the 



