jAmjABY 13, 1911] 



SCIENCE 



47 



HYPOTHESIS OF IONIC CUKEENTS 



According to the measurements of Ruther- 

 ford and Zeleny, the average total ionic 

 velocity for dry air at the earth's surface 

 and an electromotive force of one volt per 

 centimeter, is 3.2 cm./sec. At this rate it 

 would take forty years to encircle the 

 earth. Putting together all the facts of 

 laboratory experiments at present avail- 

 able to me, including the work carried out 

 at the laboratory^ here by Zeleny and 

 Kovarik, a provisional calculation appears 

 to show that, for the atmospheric pressure 

 prevailing at about the height of 75 kilo- 

 meters, the ionic velocity would be of the 

 order required for a circuit of the earth in 

 about four minutes — hence, of the order 

 found above to correspond with progres- 

 sion of the observed times of beginning of 

 a sudden magnetic perturbation. 



A mathematical analysis of the mag- 

 netic observations made at various points 

 on the earth's surface has revealed the ex- 

 istence of a definite system of atmospheric 

 electric currents whose magnetic effects 

 are of sufficient magnitude to require their 

 being taken into account when determining 

 the so-called magnetic constants of the 

 earth. Now if the atmosphere is made 

 more conducting at any point, as the re- 

 sult, for example, of the ionizing efEect 

 from solar radiations, an extra current 

 will be started and set in motion by the 

 electromotive force existing at that point. 

 The direction finally followed by the extra 

 current will, however, not depend alone 

 upon the prevalent electromotive force, but 

 also upon the deflecting effect of the earth 's 

 magnetic field and of the earth's rotation 

 on the electric carriers, and doubtless upon 

 a variety of other conditions. 



If a negative ion is set in motion at a 

 given altitude in an eastward direction, 



^The Physical Laboratory of the University of 

 Minnesota. 



the deflecting effect of the earth's magnetic 

 field will be to bring it down closer and 

 closer to the earth. But the ionic velocity 

 decreases with decrease of altitude, hence 

 the magnetic effect produced by the moving 

 charge on a needle at the earth's surface 

 will begin later and later, as the charge 

 travels eastward. If, on the other hand, 

 the negative ion starts westward around 

 our planet, then the deflecting effect of the 

 earth's magnetic field would be to make 

 the charge move higher and higher and, 

 hence, faster and faster. We might thus 

 possibly have the following state of things : 

 Due to some cause, electric charges are set 

 in motion in every direction from a certain 

 point overhead. Those with an easterly 

 component of motion have their velocities 

 checked in the manner just described, 

 whereas those with a westerly component 

 are made to move faster, so that for two 

 stations, one east and one west, the mag- 

 netic effect is recorded later at the east 

 station. This deduction you wiU observe 

 would correspond with that actually found 

 for the vast majority of the 38 disturb- 

 ances above treated. In brief, the deflect- 

 ing effect of our own magnetic field would 

 be favorable towards the maintenance of 

 easterly progressing negative ions, since by 

 bringing them closer to the earth their 

 effect is increased, and unfavorable for the 

 westerly ones since they are made to move 

 farther and farther away from the earth. 

 Whether it is due to this fact that a sudden 

 disturbance progresses more often to the 

 east than to the west is an interesting 

 query. 



THE PECULIAE MAGNETIC DISTURBANCES OF 

 DECEMBER 29-31, 1908 



I want to make you acquainted next with 

 another set of most instructive magnetic 

 disturbances which differs from the kind 

 previously considered in several important 



