( 208 ) 
I further investigated whether any connection existed between the 
frequency of the Spasms and the tropical and the synodical revo- 
lution of the moon, respectively 29,5306 and 27,3216 days; and 
moreover with the sun’s rotation, for the periods: 25,787; 25,800; 
25,815; 25,857; 25,929 and 26,071 days. 
In none of these cases however was a marked periodicity found, 
at all events nothing pointing to a direct influence of these revolutions. 
Such an influence would have been useful for the explanation 
of the phenomena we are now considering. 
It is. not possible now to give an explanation; for that purpose 
we require, that 
Ist. The Microvariometer should furnish new material for research ; 
gnd. The phenomenon is also investigated at other magnetic 
observatories ; 
34, A theory of tbe variation of the earth’s magnetic force, of 
the Aurora borealis and of the electric currents in the earth and 
the high atmosphere has been established. 
I will only point out some analogies, which may perhaps con- 
tribute afterwards to an explanation. 
The deviations, calculated according to VAN DER SToK’s method 
of reduction, can serve as an indication of the amount of distur- 
bance of the Horizontal Intensity at Batavia, especially for the 
shifting of the lines. The table‘) for the period 1892—93 shows 
for these deviations 
Ist. A semi-annual period, with its maxima in March and Sep- 
tember, its minima in June and January. 
2nd, A diurnal period, with its maximum at 3 P.M. and its 
minimum at 1 A.M. 
34, A concordance with the number of sun-spots. 
Hence there is agreement between the annual variation of these devia- 
tions with that of the Spasms, but not between the diurnal variations. 
The photograms giving the Potential of atmospheric electricity 
show nothing in particular during Spasms, the diurnal variation of 
the Potential is even reverse and is not semi-diurnal. The annual 
variation again only contains one maximum and one minimum. Co- 
incidences in the variations of the meteorological elements are not 
to be detected. Important coincidences are found with the periodical 
fluctuations cf the Aurora borealis here, in the nightly maximum 
and the semi-annual periodicity characteristic of this. 
The observed numbers have shown, that the epochs of the maxi- 
1) Observations, Batavia, Vol. XVI. 
