222 ELECTRICAL CURRENTS OF THE EARTH. 



Courmayeur, were brought iuto requisition. The wire was the usual 

 ii'oii one, from 3 to 4 millimetres (^-iuch) in diameter. 



Before the experiments, the entire line had been inspected, repaired, 

 and insulated with care, so that there was no sensible movement in the 

 needle on introducing a current into the line, while the opposite end 

 was insulated in the air. I emph\ved the usual electrodes of zinc, im- 

 mersing tbem in the water of wells when I could, or introducing them 

 into holes made in the ground and tilled with identically the same water, 

 which was that of the Dora. Between Ivrea, St. Vincent, and Aosta, 

 the experiments were always made in the night, when the telegraphic 

 offices were closed ; in the last experiments between Aosta and Cour- 

 mayeur, where the telegraphic service ceases in September, the experi- 

 ments might be made with confidence at any hour of the day. The 

 results obtained in the first series of experiments, as heretofore de- 

 scribed in the Gomptes-rendm of the Academy of Paris, (September 19, 

 1804,) were as follows: The electric currents obtained in the three lines 

 of the valley of iVosta, notwithstanding the much greater resistance of 

 the metallic portion oi^ these. lines in comparison with the line of 000 

 metres, (1,009 feet,) on which I had operated in the hills near Turin, 

 gave with the same galvanometer much stronger currents, measured by 

 the deviations more or less fixed of 40^, 00°, and even 80°, instead of 

 20° to 25° at most obtained in the shorter line. At all times, when the 

 deviations became fixed — and this was sometimes the case, even for the 

 space of an hour — the deviation indicated an ascending current in the 

 metallic line. But a certain tremor of the needle was noticed, and from 

 time to time, as in the experiments between Pontedera and Volterra, 

 the needle descended suddenly to 0°, about which it oscillated, or even 

 passed into the opposite quadrant, returning afterwards to the fixed 

 deviation [)rescribed by the ascending current of the wire. In this case, 

 also, I have every reason to believe, though I will not absolutely atfirm 

 it, that no voltaic current was introduced at such moments into the 

 circuit so as to produce the oscillations in question. 



The experiments made in November, 1800, were conducted under 

 better conditions when the correspondence between Courmayeur and 

 Aosta had been suspended for two months. In these I was assisted by 

 Siguor Eccher, adjunct of the chair of physics in this museum, to whose 

 zeal and lo^e for science it is due that even under unfavorable circum- 

 stances of weather and place, especially in the winter, all possible pre- 

 cautions were used m order that the experiments might yield exact 

 results. At each extremity of the line three similar vases of earth were 

 sunk -U a formation of nearly identical qualities at a certain distance 

 from one another, and the current was measured by transferring in 

 succession the electrodes of zinc immersed in porcelain cylinders and 

 ascertained to be homogeneous, now to one and now to another of the 

 earthen vases, all of which, at either extremity, were filled with water 

 from the same source. 



The experiments between Aosta and Courmayeur were made on the 

 3d of November, 1800, at 8 o'clock in the morning; the atmospheric 

 electricity at Courmayeur was feebly positive ; snow had fallen in the 

 night on elevated places, and the clouds were dissipated only at the 

 rising of the sun. At 8.45, the line was tested in order to ascertain its 

 insulation, which was found to be perfect. The experiments yielded 

 the following results : 



