PART III. EARTH CURRENTS AND KARTH MAGNETISM. CHAP. I. 731 



The opinion expressed by Wild, Weinstein and others on the one side, and Blavier on the other, 

 cpresent the two extremes. We think that the right explanation will be one which unites the two 

 xtreme cases into one theory. 



In fact we think that recent investigations on terrestrial magnetism have already made it possible 

 look into the complexity of earth currents with a keener eye than it was possible for those who 

 /ere working some years ago. 



Through the works of A. SCHUSTER('), von BEZOLD and AD. SCHMIDT, we are already familiar with 

 K- idea of extraterrestrial currents. The existence of such currents is a necessary consequence of the 

 ypothesis that magnetic disturbances are the effects of electric radiation from the sun. 



My previous research ( 2 ) as to the cause of various disturbances has shown that at any rate at places 

 car the poles, most magnetic disturbances are due to peculiar current-systems above the surface of the earth. 



The view we take as regards the cause of magnetic disturbances will necessarily influence the view 

 e take as regards their connection with earth-currents. If our hypothesis is right, we shall certainly 

 et currents induced in the earth on account of changes in the external currents. 



Recently van Bemmelen in his paper, "Registrations of the earth-currents at Batavia for the investi- 

 ation of the connection between earth-current and force of earth-magnetism", treats the earth-currents 

 om the point of view, that they may be considered as currents induced by external currents. 



He finds the ratio of the amplitudes in the earth-current registerings to the corresponding magneto- 

 ieter-records to increase as the time of oscillation diminishes and usually finds a difference in phase 

 etween the earth -current oscillations and those of the magnetometer. 



ARTH-CURRENT REGISTERINGS AT KAAFJORD AND BOSSEKOP, 19021903. 



144. At our stations Kaafjord and Bossekop, the earth-currents were recorded in cables, 400 metres 

 ng and resistance 1.55,?.?, one directed along the magnetic meridian and another perpendicular to it. 

 he cable-system formed a cross with equal branches, in the centre of which the instruments were 

 troduced. 



The galvanometers employed were of the type Deprez-d'Arsonval, and were placed as a shunt on 

 >e principal line, as indicated in the accompanying figure. 



The current measured in this manner on the galvanometer, will be a standard for the component 



the earth-current which goes in the direction of the connecting line between the two earthplates, 



, if preferred, for the component of the electromotive 



rce occurring in this district. 



The earth-current conditions will be to some extent 

 mnged when the cable is introduced. This might be 

 ;sumed to have special influence if the resistance in the << 

 ible is small in comparison with the earth-resistance. If, 



i the contrary, a great resistance is introduced into the 



^ 'fOO" 1 



rmer, it will not have any appreciable influence. 



Fig. 269. 



How important a part this may play it is not easy 

 say; but in any case it will not exert any essential influence in the main phenomena. 



The influence of the polarisation of the earth-plates will be very considerable where the lines, as 

 this case, are short. Here, therefore, it is only the brief variations that are suitable for investigation 



7 



Earth 



(') A. SCHUSTER: Phil. Trans, of R. S. 180, p. 467, 1889. 



I 3 ) Expedition Norvegienne 18991900. Parti of the present work. 



