ELECTRICAL CURRENTS OF THE EARTH. 



219 



many experiments I have used another but similar line, whicli enabled 

 me to test, by comparison with one another, the two electrodes immersed 

 in close contiguity, now in the lower station, now in the ui>per. The 

 electrodes were the usual plates of amalgamated zinc, immersed in the 

 solution of sulphate of zinc contained m porcelain cylinders, which cyl- 

 inders were immersed in turn in well or spring- water contained in two 

 vases of terra-cotta, buried in the earth. It is useless to state that 

 these electrodes were hrst tested, and that every precaution was used 

 to ascertain their homogeneitj^ At the two extremities, after selecting- 

 a soil having- very nearly the same qualities, I excavtited two holes, with 

 a width and depth of one metre, {3 feet,') Ayhich I hlled with the same 

 earth, and into the holes thus prepared introduced the vases with the 

 two electrodes. On each day of experimenting, I began and finished 

 by reversing the position of the vases, in order to assure myself that 

 the deviations were independent of the electrodes, and that, when tested 

 in contact, the latter were perceptibly homogeneous. The difference of 

 level between the two electrodes was about 55 metres, (ISO feet.) 



Simultaneously with the observations of the electric currents in the 

 circuit, I studied at the extreme stations the atmospheric electricity in 

 the way already described. On clear and calm days I have alw'ays 

 found very strong- signs of positive electricity near the upper station, 

 and no signs or very weak ones of the same electricity in the valley 

 below, near the lower station; indeed, at this station tlie same thing- 

 occurred even in stormy weather. At the upper station the signs 

 changed according to the intensity and distance of the existing storm, 

 as Ave shall again mention. I select the numbers obtained on the 2d, 

 3d, and 4th days of July, when the air was warm and dry, and the 

 weather calm with the exception of a distant storm which was observed 

 on the 3d, some hours after midday. On the 2d, from morning until 10 

 at night, the current continued to ascend in the metallic line, and re- 

 mained fixed at between 15° and 10° during- the morning, and between 

 11° and 12° iu the afternoon. The results of the 3d were the following : 



The electrodes having been left in place all night, the current Avas 

 found the next morning, fixed at between 14° and 15°, and the same 

 deAiation remained on reversing the position of the electrodes. 



I report also the numbers obtained May 30, on which day a peculiar 

 storm occurred, a strong sirocco Avind having prevailed. Avhile for some 

 time the sky was covered Avith dense clouds traversed by electric dis 

 charges in the distance. Eain also fell. 



