ON THE PERIOD OF THE ROTATION OF THE SU 
AS DETERMINED BY METEOROLOGICAL DATA, 
BY 
Dr. J. P. VAN DER STOK. 
1. In the »Observations made at the magnetical and melent 
logical Observatory at Batavia”, Vol. ІХ, Appendix Ш, the resulls 
were given of an investigation, according to HonNsTEIN'S method, 
into the existence ‘of a twenty-six-day period of Багошеше 
daily means and ranges, by which it was proved that, by 
this method, а periodical variation of the daily means might 
be demonstrated and that no trace of this phenomenon in the 
daily oscillation was observable. The above method, however 
is open to several objections and, although it certainly has | 
done excellent service in pointing out the existence of this | 
variation, it is inadequate for obtaining an accurate deter: 
mination of the period and the amplitude of the variation, the 
latter being in all cases, even in high latitudes, very smal 
with respect to the disturbing influences to which the dati. 
from which it has to be calculated, are subjected. | 
Proof has repeatedly been given in these publications thal 
the now twenty-two-yearly series of hourly meteorologie 
observations is unequalled when the object is to detect 28 
determine periodical variations of very small amplitude. қ 
fact, if the lunar atmospheric tide be taken as an examP" 
the conclusion to which Dr. van Besser (1) arrived, that in high 
latitudes even а thirty-yearly series of observations is insufficient 
to obtain a well defined and smoothly running curve, may" 
safely endorsed, whereas at tropical stations such as Вајат» 
% Handbuch der Witterungskunde, Theil 1, S. 118. 
