218 



ELECTRICAL CURRENTS OF THE EARTH. 



It is impossible to discover in tlie numbers here reported any relation 

 between the intensity of the terrestrial current and the hour of the 

 day. The augmentation observed at the close of the IGth day, aud in 

 "the morning of the 17th, was probably owing to the rain which fell in 

 that interval, and in fact this result never fails to be obtained when we 

 sprinkle two or three buckets of water around the electrodes. In the 

 first hoiu\s of each of the days cited, I assured myself of tlie homoge- 

 neity of the electrodes by immersing them simultaneously in the water 

 and from time to time reversing tlieir position. The most important 

 in'ecaution is that of frequently ascertaining that the water maintains a 

 constant level in tlie cavities in which are immersed the porcelain cylin- 

 ders of the electrodes. 



I further report the numbers obtained in one of the observations 

 ■which I conducted with the electrodes suspended in two wells, one at 

 the top, the other at the base of the hill before mentioned. These num- 

 bers were obtained with the galvanometer of 1,,500 coils. In this exper- 

 iment the position of the electrodes was twice mverted. 



It is evident from the above that tlie deviation produced by the use 

 of electrodes floating in the water of wells is more constant than that 

 resulting from their employment when sunk, as we have described, in 

 the earth, for in the latter case the water in which the cylinders are 

 immersed is continually decreasing. I ought here to observe that, 

 having taken advantage of a well, situated midway on the slope of the 

 hill of Turin, I repeated these experiments with the same length as 

 before of the metallic line, and in one case with a stratum of earth ex- 

 tending from the base to about the middle of the hill, and in the other 

 case from the middle to the to^), the electrodes being all the time im- 

 mersed in wells; in the experiments in which the terrestrial circuit was 

 thus about half that before used, the fixed deviation of the ascending 

 current was 10° ; much less therefore than that obtained between the 

 base and summit of the hill , 



I deem it proper further to describe the principal results derived from 

 an uninterrupted series of experiments made through all the months of 

 last summer, in the hills around Florence. The line was composed of 

 the usual copper wire covered with gutta-percha, suspended upon poles 

 and interrupted about midway of its entrance into the laboratory, where 

 the two ends were immersed simultaneously with the wires of the gal- 

 vanometer of 1,500 coils, in two small vases filled with quicksilver. In 



