PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 8oi 



To enable a comparison to be made with these, we have put together, for = 40, which about 

 answers to the position of Berlin, the current-components for two systems of this kind. 



One of them answers to an external inducing current at the equator, where L 2/?, and which 

 ies nearest to the earth at a place answering to Noon; the second answers to a rectilinear current 

 jarallel with the plane of the equator, lying at a least height, // = 0.25 R, above a point in a small 

 :ircle round the pole with a spherical radius of 20, where the time is 2 h a. m., a night-system corres- 

 aonding to a negative polar storm. 



The strength of the current in the equatorial system is put at 20 times greater than the strength 

 it the current in the polar system. 



The vector diagram that has been drawn (fig. 288) shows us the suggestive agreement that exists 

 n the main between this and the vector diagrams that Weinstein has calculated from observations, one 

 t" which we here reproduce (fig. 289). 



\Ve must emphasise the fact that in this first experiment we have not taken into consideration the 

 rays that at about 6 h 7'' p. m. must penetrate into the polar regions just where we have been 

 ed to assume that the rays which produce the positive polar storms descend towards the earth. 



This group of rays will be included in our future calculations, as a preliminary investigation seems 

 o show that in this way a surprisingly close agreement may be obtained between calculated and observed 

 diagrams. 



It may further be noticed that in the equatorial system in a latitude of about 50, i. e. ft -= 40, 

 he currents are as a rule only in a direction N S. 



llnse currents will now approximately be proportional to , i. e. to or, in other words 



am ? 3(j 



ar 



o , in accordance with what Dr. Steiner has found. 



\Ve can therefore, from our points of view, find a natural explanation of all the hitherto known 

 >rincipal features of the diurnal variation of earth-currents. 



\Ve will not at present, however, go more thoroughly into the matter of the diurnal variation of 

 errestrial magnetism, but will reserve it for a subsequent chapter. 



