ELECTRICAL CURRENTS OF THE EARTH. 



21' 



of the as(^eiuling- current was not altered by the substitution of the 

 copper wire covered with gutta-percha for the insulated iron wire, nor 

 were any differences noticed when the wire was extended on the ground 

 covered with grass or with snow. 



I have seen the intensity of the current increased by placing the 

 electrodes in the ground at a depth of 10 centimetres (4 inches) below 

 the bottom of a pit from 1 to L* metres (3 to 7 feet) deep ; and while in 

 excavations of inconsiderable depth, the ascending current has marked 

 from 15° to 1(P, in those much deeper, and in wells, it has indicated 

 more than 20^. When the electrodes are in a very superficial stratum 

 the deviation is less fixed than when they float in tlie water of wells. 

 In the latter case the deviation remains constant from hour to hour, if 

 the day is clear and calm, nor is it changed by reversing the position of 

 the electrodes in the wells. 



It may, I think, be of use to cite here a series of numbers v.iiich 

 exhibit the deviations realized on certain days of July, 1804:, v.ith elec- 

 trodes sunk in excavations having a depth of 2 metres (7 feet.) The 

 atmospheric electricity was of moderate intensity and constantly posi- 

 tive; tlie sky in part clear, and in part overcast. The galvanometer 

 with which I operated was one of 2,000 coils. 



