298 ON EARTH-CURRENTS. 



The diurnal changes of the intensity of the disturbance-currents 

 present features equally marked. In order to perceive them 

 clearly, it may be convenient to examine separately the meridional 

 currents, and those at right angles to the magnetic meridian. 



The meridional currents are developed chiefly at the European 

 stations, and at Toronto, in Canada: at Athabasca, and at the 

 southern stations, they are comparatively small. The northerly 

 maximum occurs at Toronto, at 9 p. M., at Munich at 10 p. M., and 

 at Dublin at 11 P. M. Its epoch at Makerstoun is between 9 p. M. 

 and 11 P. M. The southerly maximum occurs at 8 A. M., very nearly, 

 at the four stations. Thus the epochs are nearly at the same hours 

 of local time, notwithstanding the differences of longitude. 



A similar result appears from an examination of the currents 

 at right angles to the magnetic meridian. Thus, in the northern 

 hemisphere, the easterly maximum occurs between 2 A. M. and 

 4 A. M., and the westerly maximum (or easterly minimum) between 

 3 P. M. and 5 p. M. The two epochs are precisely the same at 

 Makerstoun and at Toronto, places which differ more than five 

 hours in longitude. 



The corresponding epochs for the two stations in the southern 

 hemisphere in like manner agree with one another. The easterly 

 maximum occurs between 6 p. M. and 7 P. M. at St. Helena and at 

 the Cape of Good Hope, and the easterly minimum between 5 A. M. 

 and 6 A. M. It is deserving of remark that these epochs do not 

 differ considerably from those of the opposite movements in the 

 northern hemisphere, the easterly extreme in the one corresponding 

 nearly with the westerly extreme in the other. A similar opposition 

 in the phenomena of the regular diurnal change in the two hemi- 

 spheres was pointed out by the author on a former occasion, and 

 there seems good reason to suppose that the two facts are physically 

 related. 



It appears, then, that the principal epochs of the disturbance- 

 currents are connected with the sun's hour-angle, and are inde- 

 pendent of the longitude of the place at which they occur. 



The foregoing relations appear to be of a very general nature, 

 and such as to afford a distinct basis for physical theory. 



