46 



Art. 9. -T. Terada: 



16. Since in the above investigations, the trains chosen 

 from among the records of 1913 were those especially regular 

 and moreover, the periods were determined with special care, 

 the material seems appropriate for studjdng the frequencies of 

 different periods in different hours of the day, in spite of the 

 relatively small number of trains taken. The results of the ex- 

 amination are tabulated below, which show remarkable predomi- 

 nance of the longer waves in the night hours, as already remarked 

 in §9. 



Table IX. Number of trains. 



17. Rotatory character of the horizontal components. As 

 already mentioned, the horizontal components of the periodic 

 disturbing field show as a rule more or less rotatoiy character. 



Fig. 17. 



clockwise 

 cou-nterclocRwisc 



To investigate the relation 

 regular waves 



in detail, 



with decidedl}^ rotatory 

 character were chosen from 

 the records of 1913, at the 

 same time with the investi- 

 gation of the pieceding 

 article. The data obtained 

 were classified into two 

 groups, i.e. those which 

 showed regular rotation in 

 the clockwise and in the counterclockwise sense respectively. 



30 



20 



I 



I z 



16^ 



20" 



24-^ 



