296 ON EARTH-CUERENTS IN CONNEXION WITH 



from observations made by himself, which, although derived 

 from a shorter series of observations, are of the highest scientific 

 value. For these places, therefore, it only remains to combine 

 the results of the declination and horizontal intensity, by the 

 method which has been already applied to the regular changes 

 of the same elements. 



The result of this calculation, applied to the Dublin observa- 

 tions, shows that the direction of the disturbance-current at that 

 place observes a mean law, not very dissimilar to that which 

 governs the regular diurnal current. Its azimuth rotates, during 

 the day, in the same direction as the sun, its direction pointing 

 almost exactly to the luminary. The direction is east about 5 A. M. ; 

 south, about noon ; and west, at 6 p. M. The current is easterly 

 from 9 p. M. to 9 A. M., inclusive, and westerly during the remainder 

 of the 24 hours. The mean azimuth of the easterly current, 

 measured from the north eastward, is 40 15' ; that of the westerly 

 is 230 18'. If the mean directions of the easterly and westerly 

 currents be assumed to be in the same right line, the mean 

 azimuths will be N. 45 E., and S. 45 W. This result agrees, 

 in a very remarkable manner, with those obtained by Mr. Barlow 

 and Mr. Walker from the direct measures of the intensity of the 

 earth-currents, as observed on days of disturbance in several of 

 the telegraphic lines of England; and the agreement must be 

 regarded as an additional proof of the dependence of the magnetic 

 changes upon earth-currents. 



The phenomena at Makerstoun are very similar to those at 

 Dublin ; and the epochs of the passage of the current through the 

 cardinal points are nearly the same. 



At Toronto, in Canada, the current is wholly easterly, the mean 

 azimuth being 81 25'. On the other hand, at Athabasca, the 

 current is easterly from 12 p. M. to 6 A. M., inclusive, and westerly 

 during the remainder of the 24 hours. The sums of the easterly 

 and westerly changes for the entire day balance one another, the 

 easterly currents being as much greater in magnitude as they are 

 less in duration. Their mean azimuths are 110 18' and 290 56'. 



At St. Helena the direction of the current is easterly throughout 

 the day, the mean azimuth being 70 53'. The direction is singu- 

 larly constant, the greatest deviation from the mean being only 

 10. The phenomena at the Cape of Good Hope closely resemble 

 those at St. Helena. The direction of the current is easterly at 



