1904. No. 2. THE DIURNAL VARIATION OF TERRESTRIAL MAGNETISM. 33 



2. In a magnetically calm period at the equinox, the sun, at that part 

 of the day when it is below the horizon of the magnetic north pole, 

 may be presumed to maintain a fixed in\ariable system of electric 

 currents in space outside the earth. 



3. This system of currents consists of several parts, of which the most 

 prominent, an approximately circular current, lies in a plane that is 

 tangent to the earth's surface at about 31° N. Lat., in such a manner 

 that the point of tangency is the centre of the path of the current. 

 The observations at hand only allow of the construction of the nor- 

 thern half of the current; but if we assume that the path of the 

 current is a complete circle, its most southerly portion must very 

 nearly intersect the line of direction from the sun to the earth. The 

 radius of the current-circle is about 3800 km., and it flows at an 

 altitude of about 1000 km. above the surface of the earth. 



4. On each side of the main current, which has a cyclonic character, 

 the observations indicate the path of an anticyclonic current. 



;. In the southern hemisphere, the otherwise more than meagre amount 

 of observations indicates a corresponding cyclonic main current with 

 an anticyclonic current on each side. 



These results, when viewed in conjunction with what Schuster and 

 von Bezold have previously found, seem to me so promising that they 

 call for wider investigations after the synoptic method I have employed, 

 but with more ample material in the way of observations than was at my 

 disposal. I will especially draw attention to the importance of very care- 

 ful investigation as to the part played in the normal diurnal variation of 

 terrestrial magnetism by the earth's magnetic field nearest the magnetic 

 poles. 



Printed 5 March. 190^. 



