50 



Art. 9.— T. Terada 



magnetic field due to the current passing near the point A, 

 counted positive toward W from N of A, is given by 



sin 6 sin ?. 



sni a = 



\/l— (cos 6 sin ^ + sin 6 cos ^ cos /Î)- 

 Putting for example, <P—od° and (?=30°, 40° or 50°, the variation 

 of a as the function of ?. is shown in the annexed figure (Fig. 19). 



Fig. 19. 



360 X 



To compare with Fig. 16, the present figure must be properly 

 shifted along the axis of ?<, which is equal to the hours, up to an 

 additive constant. It seems that the meridian corresponding to 

 the pole P, (i.e. ?-=0) of the assumed circular current may be 

 placed somewhat in the early hours of the morning. The shapes 

 of the curves, however, do not agree so well as to enable us to 

 determine the most probable value of d. Indeed, it will be too 

 much to infer at once the existence of such a simple circular 

 current in view of the above consideration, based on the 

 observation at a single station. Still the orientation of the 

 different portions of the atmospheric current, of wliich the 

 fluctuations may produce the magnetic pulsations, must resemble 

 in some measure that of the corresponding portions of the ideal 

 simple system above considered, and must in any case be directed 



