224 ELECTRICAL CURRENTS OF THE EARTH. 



ground at the depth of a metre, (3 feet,) were tried as electrodes, and 

 the deviation obtained, the needle continuing nearly immovable, was 

 from 114° to G50. 



GENERAL CONCLUSIONS. 



The experiments described in this memoir point to the following con- 

 clusions : 



1. If a metallic line be insulated from the ground or suspended at a 

 certain heiglit, or in actual contact with the ground, and its extremities 

 be sunk in the earth, in good communication with the latter by means 

 of perfectly homogeneous electrodes, with a certainty that there does 

 not exist any electro-motive force between the parts of the metallic cir- 

 cuit, or between the earth and the electrodes, it will be found that there 

 is in that line a constant circulation of electricity, whenever the line, 

 having a rectilinear length of at least G kilometres, (4 miles,) has its ex- 

 tremities sunk very nearly at the same elevation and in a horizontal 

 stratum, or, if the length of the line be much shorter, when its extremi- 

 ties are sunk in the ground at a different degree of elevation. 



2. When a metallic line has a length of kilometres, (4 miles,) and 

 its extremities are sunk in a horizontal stratum, there is in that line a 

 current having a constant direction from south to north, if the line be 

 extended on the meridian ; if the wire be extended in an equatorial di- 

 rection, the signs of the electric current which circulates therein are 

 very variable and without a fixed direction. 



3. In a metallic line much shorter, say 300 metres (984 feet) to com- 

 mence with, there is a constant circulation of electricity, if the extremi- 

 ties are sunk in the ground at a different elevation as regards one an- 

 other. In that case, the current is one constantly ascending in the me- 

 tallic line. 



4. This ascending current has an intensity which, notwithstanding 

 the greater resistance of the circuit, increases with the length of the 

 circuits, and increases also with the difference of level of the j)oiuts at 

 which the extremities of the line are sunk. But in circuits which are of 

 considerable length, and in which there is a great difference of altitude 

 between the extremities, the intensity of the ascending current is not 

 so constant as in short circuits. 



These results change in the presence of storms, and also in great at- 

 mospheric perturbations ; in such cases the intensity of the terrestrial 

 current, and likewise its direction, are subject to very considerable va- 

 riations. 



HypotJiesis rcspccthuj the origin of the terrestrial current. — I shall be 

 very brief on this point, as these researches are still deficient in that ex- 

 tent which would be requisite for success in interpreting a phenomenon 

 necessarily obscure and highly complicated when submitted to rigorous 

 investigation. 



When we consider that the resistance to the electric current of a ter- 

 restrial stratum is nearly null, and that it does not vary with the length 

 of the stratum, it is not easy to see an analogy between these currents 

 and derived currents properly so called. 



Associated as the terrestrial currents are with the apparition of the 

 aurora borealis, and with the great variations of terrestrial magnetism, 

 the probability naturally suggests itself of an intimate relation between 

 these currents and the causes of the magnetism of the earth, as well as 

 of the electric state of the earth itself and of the air. If, as has been 

 proved by experiment, the earth is a body charged with negative elec- 

 tricity ; if, as in effect is the case, the tension of this electric state of the 



