292 



ON EAKTH-CURRENTS, AND THE DIUKNAL 



19. From a review of the preceding, we are enabled to see what 

 are the laws of the earth-currents common to all, or to the greater 

 number of the places of observation ; and to ascertain in what 

 manner, and to what extent, these laws are departed from in par- 

 ticular instances. And from a consideration of the physical cir- 

 cumstances of the localities in which these deviations occur, we 

 may, in some cases at least, be enabled to trace them to their 

 probable origin. 



I. In the first place, then, it will be seen that at most of the 

 stations in the northern hemisphere the direction of the current 

 changes, throughout the day, according to the same general law. 

 This will be evident from the annexed Table, which contains the 

 hours at which the direction of the current passes through the car- 

 dinal points at the undermentioned stations. 



TABLE IX. 



Direction of the Currents. 



From this Table we learn that the times of passage of the cur- 

 rent through the east, south, and west points, vary within narrow 

 limits. The means are : 



Mean time of easterly current, . . . 10 h 36 m A.M. 

 southerly current, . . 2 30 P.M. 



westerly current, . . . 7 10 p. M. 



The mean time of the south meridian passage is earliest at Bar- 

 naoul, and latest at Nertchinsk. The times of the north meridian 

 passage differ much more widely, the mean epoch being 3 u 10 m A. M. 

 for the east of Europe, and for the west of Asia, and 7 h 10 m A. M. 

 for the west of Europe, the east of Asia, and America. 



