220 M. P. A. Reslhubei' on the Decennial Period in the 



Magnitude of the Daily Alteration of the Declination from 

 8 o'clock A.M. to 2 o'clock p.m.* 



I must remark here in explanation, that these i-esults do not 

 express the full magnitude of the daily variation; for, according 

 to my investigations of the hourly change of the declination 

 during the day, the minimum declination occurs with us at 7 

 o'clock in the morning, Gottingen time, the maximum at 1 o'clock 

 P.M. Gottingen time ; hence at 8 o'clock a.m. and at 2 o'clock 

 P.M. the declination had already decreased a little, and therefore 

 the quantities noted are a little too small, but certainly not con- 

 siderably so ; at all events they are sufficient to show clearly the 

 existence of the periodical alteration. 



The mean magnitude for the year attains a minimum between 

 1843-44, a maximum from 184*8 to 1849. 



I subjected the monthly mean magnitude of the daily change 

 of declination fi-om 1842 to 1850 inclusive to a strict calculation, 

 according to the method used in the case of periodic phsenomena, 

 and obtained for the annual course of the above change in the 

 daily declination the following result : — 



* The quantities wanting in 1842 and 1843 are obtained by interpolation. 



