ON THE ELECTEICAL CURRENTS OF THE EARTH. 307 



current between these cavities, as I had obtained none in employing the two 

 porous cylinders with their plates of zinc plunged in a vat filled with water. I 

 proposed also to test beforehand whether the nature of the formations in which 

 the pits were excavated might have some influence. With this view 1 caused 

 the earth proceeding from the excavation of pits near the place where I was 

 established to be transported, and two cavities formed in a neighboring field to 

 be filled with it; having then introduced into this earth, in the manner already 

 described, the extremities of the galvanometer, I obtained no sign, of a current. 



Ver\" near the place where the two lines, north-south and east-west, crossed 

 one another, each of the lines was interrupted, and the extremities thus obtained 

 were passed into two capsules filled with mercury in the chamljer where 1 had 

 stationed myself with the galvanometer. I employed alternatelj" three ga^lvan- 

 ometers — one of 1,500 coils, another of 100, and a third of 24,000 coils ; the 

 numbers which I shall report in ni}- memoir were obtained with the first of them, 



I must be excused for these long details on the process which I employed; I 

 have thought it necessary to give them, as well by reason of the importance of 

 such researches as of the difficulties and uncertainty met with in the investiga- 

 tions which I have before cited. I continued the experiments on the two lines 

 for nearly a month, fi-om the 12th or loth of March to the 1.5th of April of the 

 present year, duiing which time the weather was generally fair, the air cold and 

 dr}', the sun very warm. I cannot report in this abstract all the numbers obtained 

 in this long series of experiments ; for ten days the observations were made 

 almost hour by houi", with a change of ol)servers. I am compelled, therefore, 

 to give here onlj^ a recapitulation of the results at which I have arrived. 



1. In two circuits, formed in the manner which I have described, it is rare not 

 to find electric currents more or less constant, whose origin cannot be attributed 

 absolutely to the heterogeneousness of the terminal metallic plates, nor to chemical 

 action between the water in which the plates are immersed and the terrestrial 

 strata. 



2. These currents augment in intensity by deepening the cavities into which 

 the terminal plates are plunged from O'^.SO to 2 metres; the greater conducti- 

 bility found in the mixed line l)y deepening the terminal cavities accounts for this 

 result. The same may be said of the slight and transient augmentation of the 

 electric currents which is reafized by the eftect of rain on the earth immediately 

 surrounding the cavities in which the electrodes are plunged. 



3. It has not been found that the extent of the plates of zinc and the diameter 

 of the porous vessels have a distinctly marked influence on the intensity of these 

 currents, when operating at a depth of two metres. 



4. In the meridian or south-north line, the current has always maintained a 

 constant direction ; hundreds of observations have continually shown tliat the 

 current entered the galvanometer by the metallic line coming from the south, 

 and issued from it through the line directed to the north. 13y comparing the 

 very nearly conformable deviations obtained in this great number of obsferva- 

 tions, it would appear that this current presents in the 24 liours two maximums 

 and two miytintums of intensity. The two minimums occur during the day and 

 in the night, at nearly the same hours, that is from 11 to 1 o'clock. After 

 1 o'clock in the night, the current augments and attains a maximum at from 

 5 to 7 o'clock in the morning. In the day this maximum oscillates between 3 

 and 7 o'clock in the afternoon. The difference of intensity between the maxi- 

 mums and the minimums of intensity is greater than that of 1 to 2. 



5. In the equatorial line the results are very different, and subject to great 

 variations. Frequently the needle rests at U°, frequently it oscillates, sometimes 

 into one quadrant, sometimes into the other, ranging from two to three degrees, 

 and even 14° and 15° on the same side, and often oscillating around 0°. The 

 direction of these cm-rents, which has occuiTed most frequently in the equatorial 

 line, was from west to east. 



