MAGNETIC DISTURBANCES. 



297 



every hour, excepting 5 A.M. when there is a slight westerly 

 movement. The mean azimuth is 77 54'. 



It thus appears that at some places as in the British Islands 

 the mean direction of the disturbance current rotates through the 

 entire compass in the course of the day; while at others as 

 Munich, Toronto, St. Helena, and the Cape of Good Hope it is 

 easterly throughout the day. While, therefore, there is a periodicity 

 in the easterly and westerly currents depending on the hour, we 

 are obliged to infer that there is, at the same time, some cause 

 constantly operating which tends to produce an easterly current. 



The mean azimuth of this current appears to be connected with 

 the magnetic meridian of the place, to which it is nearly perpen- 

 dicular. This will appear from the following Table of the mean 

 azimuths of the disturbance-currents at the northern stations, 

 measured from the astronomical and from the magnetical meridians, 

 respectively : 



The mean azimuth (magnetic) for the five stations is E. 14 N. 



The mean azimuth at the two stations in the southern hemi- 

 sphere is E. 11 S., deviating nearly as much to the south, as that 

 of the northern stations deviates in the opposite direction. It 

 thus appears that while the principal current is eastward in both 

 hemispheres, there is also a meridional current tending northward 

 in the northern hemisphere, and southward in the southern. Its 

 intensity is between one-fourth and one-fifth of that of the other 

 component. 



These results are wholly at variance with the hypothesis imagined 

 by H. de la Rive in explanation of the phenomena of magnetic 

 disturbances, according to which the disturbance-current flows 

 from north to south only.* 



* The discrepancy of M. de la Rive's hypothesis with the phenomena of the earth- 

 currents, as observed in the British Islands, has been already pointed out by .Mr. 

 Walker. It is even more marked at other parts of the globo. 



