PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. III. 551 



latitudes, which are not by any means restricted to the night side. Also if we go to regions near the 

 poles and the magnetic axis, we shall find a rapid diminution in the calmness. 



As regards Axeloen, we found the small calmness to be due, not so much to its more northerly 

 position, as to a number of centres of local storms which showed their own characteristic diurnal 

 distribution; but judging from the very great diurnal maxima of these storms, they must be mainly of 

 solar origin, and moreover we must suppose that stations so near each other as Kaafjord and Axeloen 

 have disturbances of essentially the same origin. 



The result of this investigation regarding the amount of sun-storminess has an interesting bearing 

 on the question regarding the possible influence of the moon on magnetic disturbances. If the agency 

 of whatever kind it was came from the moon the effect should show a period of a lunar day, different 

 from 24 hours. Then the moon storminess must be contained in the quantity a, and thus be extremely 

 small compared with that of the sun. 



It ought to be remembered that the alorniiiifss only contains variations of a somewhat abrupt and 

 irregular character. Then if the sun or the moon gave out a magnetically effective agency at a constant 

 rate, the effect of such an agency would not enter into the quantity we have called storminess. 



APPLICATION TO THEORY. 



107. The previous results regarding the amount of storminess due to the sun are obtained without 

 any assumption regarding the mechanism connecting cause and effect. We have merely made use of 

 facts actually found for the distribution of storms with regard to time and space. 



The next question is: How do the properties found agree with our theory ? 



Tin- characteristic properties to be explained are mainly the following: 



|i) The great storminess on the night and evening side of the earth, and in the region near the 

 auroral zone. 



(2) The calm region on the day side. 



(3) For the somewhat great storms, with their centres passing between Axeloen and Kaafjord, we can 

 distinguish two types, which we have called positive and negative polar storms. 



(4! A number of local storms occur in the vicinity of the pole to the north of the auroral zone. 



We found during the treatment of separate storms that the main features of the field of an elementary 

 storm could be explained by a system consisting of a vertical current coming in from space, and bending 

 round in the direction of the auroral zone at a height of some hundred kilometres above the surface 

 of the earth, and leaving the earth as another vertical branch. Now we have seen that the average 

 storm, which is made up of numbers of such systems, is almost entirely caused by the sun. There 

 seems then no escape from the assumption that these current systems-coming in from space, are currents 

 directly produced by electric radiation emanating from the sun. 



We can also use another line of argument. In order that the sun-effect shall mainly make itself 

 felt only within narrow regions on the earth's surface, and almost entirely on the side turned away from 

 the sun, it is necessary that the sun-agencies descend in comparatively narrow streamers, and are de- 

 viated in some way by some field of force possessed by the earth. 



Now electric rays from the sun, diverted by the magnetic field of the earth, will be just what 

 is necessary to explain this very peculiar kind of solar action. Regarding this point I must refer 

 to the publications of my experiments with the magnetic terrella in a vacuum-tube. 



Corresponding to the disturbed region near the auroral zone, we have areas of precipitation of 

 cathode particles on the terrella, forming bright spots or bands along a certain magnetic parallel which 



