16 Art. 9.— T. Terada: 



definite period from the scanty material at hand. The general 

 aspect will be seen from the annexed figure (Fig. 4). 



Fig. 4 





Since it was suspected that the number in question may 

 have some relation with the solar activity, it was compared with 

 the "provisory sun-spot number," published in Meteorologische 

 Zeitschrift, but no convincing relation could be found. ^-^ It will 

 however, be interesting to compare the present number with the 

 occurrence of sun-spots on a definite central area of the solar 

 disc.'-' 



b) These short period waves appearing simultaneously in the 

 X- and Y-components run remarkably parallel to each other 

 during the morning hours, viz. 6^ — 8^ say, every detail in one 

 component being repeated by the other with marvellous similarity, 

 no noteworthy phase difference being observed between the two 

 components (PI. V). ^Moreover, the amplitudes of the two 

 components are generally of nearly the same order of magnitude. 

 It seems as if these waves were due to the fluctuation of an electric 

 current running from NE to SW, making an angle nearly 45° to 

 the meridian. For these short waves, Z-component is com- 

 paratively insignificant and may be clearly discerned only when 

 the photographic trace is very fine. 



In the later afternoon hours, the parallelism between X- and Y- 

 components becomes imperfect. Some waves are present either in 



1) W. van Bemmeln compared the frequency of the " pulsations " with the sun-spot 

 ntimber and arrived at a negative result, loc. cit. 



2 1 E. W. Maundernoticed a 27 days period of magnetic disturbances and came to the 

 conclusion that the cause of the disturbance is to be sought on a limited portion of the 

 sun's surface, Monthly Notice of E. Astr. Soc, 65, 1904-05, p. 2, 538. The paper was 

 criticized by A. Schuster, ibid, p. 186. E. Marchand found a connection between the 

 magnetic disturbances and the sun-spots passing the central meridian of the sun's disc, 

 Congr. intern, de metéorolog., Paris, 1900, p. 148. 



