21(5 



ELECTRICAL CURRENTS OF THE EARTH. 



the day, and the other in the night, at very nearly the same hours, 

 namely from 11 to 1 o'clock. After 1 o'clock at night the current in- 

 creases, and from 5 to 7 o'clock in the morning a maximum is noticed ; 

 in the day this maximum oscillates between 3 and 7 o'clock in the after- 

 noon. The differences between the minimum and maximum of intensity 

 are a litte greater than that between 1 and 2. 



C. In the circuit perpendicular to the magnetic meridian the results 

 are very difterent and subject to great variations. It frequently occurs 

 that the needle is seen to remain at zero, or oscillates to one side or the 

 other of that point, moving from 2° to o"^ and even to 1¥^ and 15° on 

 the same side. The direction of the current most frequently observed 

 in this circuit was from west to east in the metallic part. In general 

 the needle is never fixed and sometimes executes very wide and rapid 

 oscillations. 



7. It was never noticed that the differences of temperature, which 

 fluctuated between zero (32o F.) and + 18° (05° F.) and -f 20° C. (08° F.), 

 tlie varying humidity of the air, or even rain, had any influence on the 

 direction of the current existing in the circuit extended along the mag- 

 netic meridian. 



8. These results were not varied on changing the position of the 

 metallic portion of the circuit — that is, on using the metallic line ex- 

 tended on the ground or suspended on poles. 



EXPERniENTS ON MIXED CIRCUITS OF A LENGTH VARYING FROM 

 200 METRES TO MANY KILOMETRES, THE ELECTRODES BEING SUNK 

 IN THE GROUND AT A GREATER OR LESS DIFFERENCE OF ELEVA- 

 TION. 



The first experiments of this kind were made on the hill of the Villa 

 della Begina, near Turin. The mixed circuit established there v^as 

 composed of an iron wire insulated in the usual manner, and about GOO 

 metres (1,909 feet) long in a straight line, with a direction intermediate 

 between S. E. and N. W. : the two extremities of this wire were united 

 to the usual electrodes of zinc sunk in the ground at a difference of 

 level of 150 metres (492 feet.) In these experiments also the pits in 

 which the electrodes were sunk had been tilled with the same earth, 

 and the capsules or cavities already described were then formed and 

 lined with claj'. In some of the experiments, the porcelain cylinders 

 and the zinc electrodes were suspended in the water of two wells in the 

 manner before stated. 



The experiments have been continued month after month, at different 

 seasons of the year, and not rarely the neetUe of the galvanometer has 

 been observed for entire days at very short intervals of time. I have 

 constantly found in the circuit in question an ascending curreni in the metal- 

 lic line, of an intensity v/hich in clear and calm days was constant or 

 manifested very inconsiderable oscillations. 



The x>osition of the electrodes was frequently changed, by placing 

 lowermost that which was highest, and vice-versa, yet the current 

 never varied in direction, and very slightly in intensity. For a certain 

 time the galvanometer used in these experiments was that of 1,500 coils, 

 which had served me on the plains of !San Maurizio, in the experiments 

 with the circuits of G kilometres, (1 miles,) and the intensity of the current 

 was always found to be much greater than that realized in the circuit 

 of G kilometres. The ascending hill-current was, with this galvanome- 

 ter from 20° to 25°, while that realized in the circuit of G kilometres, and 

 where consequently the resistance was much greater, never exceeded 

 from 5 to G degrees in the line of the magnetic meridian. The intensity 



