I9I0.] TERRESTRIAL MAGNETIC DISTURBANCES. 135 



It is thus seen that the disturbances of May 8, 1902, and of January 26, 

 1903, both traveled around the earth eastwardly, at an average velocity of 

 about 6,700 miles per minute, taking from 3^2 to 4 minutes to make the com- 

 plete circuit. The disturbance of May 8, 1902, as determined from the times 

 of beginning at the various stations, began in about the meridian of 75° 

 west, whereas the initial meridian for the disturbance of January 26, 1903, 

 computed in a similar manner, was found to be, roughly, 160° west. . . . 



Magnetic storms do not begin at precisely the same instant all over the 

 earth. The abruptly beginning ones, in which the effects are in general small, 

 are propagated over the earth more often eastwardly though also at times west- 

 wardly, at a speed of about 7,000 miles per mnute, so that a complete circuit 

 of the earth would be made in ^Yz to 4 minutes. For the bigger and more 

 complex magnetic disturbances the velocity of propagation may be cut down 

 considerably. The time of beginning of the disturbance may be appreciably 

 different, for the various magnetic elements, according to the character of 

 the operating systems. 



The moment it is granted that magnetic storms do not occur over 

 the earth simultaneously, then a new point of view is presented for 

 the investigation of the relation between magnetic storms and solar 

 activity, and a definite criterion is set for testing any theory ad- 

 vanced. A second decisive test is furnished by another important 

 fact disclosed by our study of the direction of motion of the two 

 magnetic disturbances of May 8, 1902, and January 26, 1903. The 

 electric currents which we should have to suppose circulating in the 

 regions above us to produce the disturbance effects as actually 

 recorded for the cases cited, would have to go around the earth east- 

 wardly, if they are to be ascribed to a motion of negatively electrified 

 particles. This is in fact the very direction in which the times of 

 beginning of the disturbances were found to progress. 



Were we to suppose now that magnetic disturbances are due to 

 the entrance in the earth's magnetic field of small negatively elec- 

 trified particles brought to us from the sun by the pressure of light, 

 or were we to adopt the hypothesis of cathode rays coming from 

 the sun, then, in either case, it would be found that the effect of the 

 earth's magnetic field is to deflect these particles in such a way that, 

 in the equatorial regions, for example, they would be made to 

 circulate around the earth from east to west. But this direction is 

 contrary to that in which we found the negative electric currents 

 would have to go for the disturbances of May 8, 1902, and January 

 26, 1903, to harmonize with the times of beginning noted at stations 



