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mum and the minimum are altered together with the geographical 
position, and that the daily variation has no secundary maximum 
at noon. We should not forget however, how Jarge the influence 
of moon- and daylight is, and how difficult it is to choose an 
adequate scale for the Intensity. At lower latitudes the maximum 
is reached a little before midnight, the minimum about six o’clock 
in the morning. 
The annual variation of the Aurora australis according to BOLLER !) 
is given by: 
Jan. Febr. March April May June July Aug. Sept. Oct. Nov. Dec. 
63 104 119 if 44 25 39 52 58 67 63 65 
which shows considerable analogy with that of the Spasms; but 
unlike the Spasms the Aurorae are more numerous during a disturbed 
magnetic state. 
It seems however that a connection exists with a series of wholly 
different motions in the curves of the Horizontal Intensity, in which 
for a time varying from a few minutes to several hours the Magnet 
regularly executes little oscillations with an almost constant period 
of about 1—4 minutes, and an amplitude of from 1 to 7 g. 
I had made these motions already the subject ofa careful inquiry, 
when a remark in the second paper?) of Prof. ESCHENHAGEN made 
it appear probable to me, that Dr. Arenpr had made already a 
similar investigation for the curves at Potsdam. 
Prof. ESCHENHAGEN writes (p. 679): “So far as has been observed 
until now, these vibrations appear principally in the daytime; at 
night they are very rare. But frequently at night larger oscillations 
occur, which are observed even macroscopically in the usual records 
and which usually occupy whole minutes, though the phenomenon 
itself seldom lasts for an hour, but usually only for a short time. 
Already at the beginning of the registering in 1890, attention was 
paid to this, as the greater distinctness and larger time-scale at 
Potsdam allowed the phenomenon to be observed there better and 
more easily than at other observatories. Since then Dr. ARENDT 
has studied this kind of waves, and he is inclined to the opinion, 
that they are connected with the phenomena of atmospheric electricity.” 
This paper of Dr. Arenpt’s “Beziehungen der Elektrischen Er- 
scheinungen unserer Atmosphiire zum Erdmagnetismus (das Wetter 
') W. Bouter. Das Südlicht. Beiträge zur Geophysik. Bd, IIL. Heft 4. $.554. 1898. 
2) Sitzungs Ber. d. Pr. Akademie d. Wiss. zu Berlin 1897. June 24. 
15* 
