TERRESTRIAL GALVANIC CURRENTS. 217 



and by means of these expressions, the intensities of 

 the northerly and westerly currents could be computed 

 for every instant. Then, assuming these to be the 

 representations of veritable currents flowing through 

 the upper strata but below the Magnetic Observatory, 

 and applying the rule of Article 88, the disturbances 

 of northerly magnetic force due to W were found, and 

 the westerly magnetic disturbances due to N were 

 found. These were compared with the actual disturb- 

 ances of northerly magnetic force (or variations of H) 

 and the actual westerly magnetic disturbances (propor- 

 tional to disturbances of declination) registered by the 

 Horizontal-Force-Magnetometer and the Declination- 

 Magnetometer respectively. And the results were as 

 follows : 



(1) In the magnetic storms, the disturbances of 

 magnetism in the horizontal plane are almost perfectly 

 explained as the effect of the terrestrial galvanic 

 currents. 



(2) On days of quiet magnetism, the magnetic 

 forces, produced by the earth-currents, follow a well- 

 marked diurnal law, which differs greatly from that 

 of the magnetic diurnal irregularities. 



(3) The galvanic currents discoverable at the 

 earth's surface do not explain ordinary terrestrial 

 magnetism. If that magnetism is to be explained 

 by such currents, they must be very deep. 



