14 Art. 9. -T. Terada : 



PART II. 

 General Results of the Investigation. 



4. The general character of the photographic records ob- 

 tained by our system of instruments may be seen in PLI. and II. 

 The time taken as abscissa increases from left to right. Upward 

 corresponds to the positive direction of each component for the 

 non-reflected trace. PI. I. is the representative record for a quiet 

 day. The trace of the sensibility determination is to be seen at 

 the beginning of the carves (marked witli-^). PI. III. is one of 

 the typical records for disturbed days, the parts of the curves 

 reflected from the " traps " are marked witli the letters Ri, Ro, the 

 suffix giving the number of reflexions. 



Even on the most quiet days, the records shows as a rule 

 numerous trains of more or less regular waves or pulsations, the 

 periods of which range from about 20 sec. to several minutes. 

 Allied phenomena seem to have been studied first by Balfour 

 Stewart^^ who found periods of 30 seconds. Kohlrausch "^ found 

 by direct eye observations a wave of 12 sec. period. Arendt^^ 

 investigated waves with periods of several minutes, frequent in 

 night hours, in connection witii his researches on the magnetic 

 disturbances associated with the phenomena of thunderstorms. 

 Eschenhagen'^-* found prevalent waves of 30 sec. which appeared 

 most frequently during daytime. Birkeland^-' studied the pheno- 

 mena for Haldde as w^ell as for Potsdam, and obtained most 

 frequent groups of waves with periods of 10 and a little longer 

 than 30 sec. More recently, van Bemmeln in Batavia"^ studied 

 similar waves with 1-4 minutes periods which he called " pulsa- 



1) Balfour Stewart, Phil. Trans. 18Ü1, p. 425. 



2) F. Kohlrausch, Wied. Ann. 60, p. 336. 



3) Th. Arendt, Das Wetter, 1986, p. 2-il and 265. 



4) Max Eschenhagen, Sitz. Ber. d. preuss. Akad. d. Wiss., Berlin, 32, 1897, p. 678 ; Terr. 

 Mag. and Atm. Elec, 2, 1897, p. 105. 



5) Kr. Birkeland, Expédition Norvégienne de 1899 — 1900 pur l'étude des aurores boréales. 

 Résultats des recherches magnétiques. Christiania, 1901. 



6) W. van Bemmeln, Verslag. Konink. Akad. v. Wet. t. Amsterdam, Proc. of the Sec. of 

 Sc, 2, 1899-1900, p. 202. 



