ON THE ELECTRICAL CURRENTS OF THE EARTH. 311 



a piece of lighted touch-wood at the upper extremity. Most frequently the elec- 

 troscope gave signs more or less strong of positive electricity, which augmented 

 suddenly at the moment of the flash. At the same instant the needle ot' the gal- 

 vanometer made a deviation of at least 15° to 20°. This sudden deviation was 

 always in the same direction, indicating an ascending current in the wire, and 

 was additional to the terrestrial current. It should be remarked that I have 

 had the opportunity of making this observation in a case in which, on account 

 of plates of copper being employed as electrodes, the current of the line was con- 

 trary to the terrestrial current which is constantly obtained with electrodes of 

 zinc. 



Thus, then, the ascending current in the wire whose extremities are sunk in 

 cavities which have a ditfereuee of level of about 150 metres, and which, from 

 the manner of operating, must be regarded as a terrestrial current independent 

 of the chemical actions of the electrodes and the strata of the earth — this current, 

 I say, augments suddenly at the moment when there is an electric discharge 

 between clouds. There remains here an important observation to be made, in 

 which, as yet, I have not been able to succeed : to notice, namely, what would 

 happen when the atmospheric electricity is negative. 



I have deemed it of some importance for the theory of these phenomena to 

 substitute for the iron wire suspended on bells of porcelain, a copper wire cov^ered 

 with gutta-percha laid upon the earth and buried as much as possible in the grass 

 and under the leaves. None of the phenomena before described in the suspended 

 line, whether with a clear sky or dming storms, have been moditied by this 

 change of the metallic line. We can conceive that during the flash of lightning, 

 at the moment when an electrified cloud, which had acted by influence on the 

 points of the ground placed within its sphere of action, discharges itself and sud- 

 denly ceases to act, a sudden neutralization may take place in the conducting 

 wire, producing the electrical eft'ect noticed with the galvanometer. 



It remains for me to report the results I have obtained by operating on tele- 

 graphic lines of great length and whose extremities were at a great ditierence of 

 level. I employed the same galvanometer and the same process of communica- 

 tion for the extremities of the line with the earth, that is to say, plates of amal- 

 gamated zinc, immersetl in sulphate of zinc, contained in porous vessels floating 

 on the water in the manner I have described. I have made three series of experi- 

 ments, one on the telegraphic line from Ivree to Saint Vincent, in the valley of 

 Aosta, 36 kilometres in length, and in which the difterence of level of the extrem- 

 ities was 281 metres. The second series was made on the line from Saint Vin- 

 cent to Aosta, 25 kilometres long, the difiereuce of level of the extremities being 

 83 metres. The third line, 27 kilometres in length, passed from Aosta to Cour- 

 majeur, at the extremity of the valley, and the difference of level of the two 

 extremities was 642 metres. The electrodes of zinc were sunk in cavities dug in 

 the ground to the depth of about half a metre. These cavities I caused to be 

 filled with the whitish water proceeding from the glaciers, which flows in great 

 abundance in the valley ; being that which, under -the circumstarices, might bo 

 considered as having in every respect the same composition. I should state that 

 the line from Ivree to Saint Vincent is nearly parallel to the meridian, while the 

 other, fronr Saint Vincent to Com-majeur, intersects the former almost perpen- 

 dicularly. 



The following were the results obtained. The electric currents in these three 

 lines, notwithstanding the nuich greater resistance in comparison witli the line of 

 600 metres on which I had previously operated, were stronger ; as were also the 

 reguhxr deviations, so as to rise from 40° to 60°, and even 80°, instead of 20° 

 and 25°, which I had realized on the hill of Turin. The experiments were 

 made at very different hours, but the regular deviation indicated in every case 

 an ascending current in the wire, as in the experiments on the line of the hill 

 just mentioned. In the greater number of cases, tlie deviation of the needle 



