54 GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



clock, the name of the observer, and remarks on .such observa- 

 tions as may be somcAvhat doubtful. An early communication 

 is ahvays greatly to be desired. Gauss. 



III. 



Extract from the daily Observations of Magnetic Declination 

 during three years at Gottingen. 



To discriminate the regular changes of declination, amidst 

 those incessant changes of greater or less amount, which we call 

 irregidar, in so far as their occuirence seems unconnected with 

 any periodical iniles, requires a great number of observations on 

 a fixed plan, persevered in for a length of time, in order to deduce, 

 by suitable combinations, mean values, freed as far as possible 

 from the influence of those anomalies by which the individual 

 declinations are affected. In general, in this part of the globe, 

 the declination increases during the forenoon, but the increase 

 is unequal on different days ; it even sometimes happens, though 

 rarely, that at the usual hour of maximum, the declination is 

 less than it was during the earlier part of the same day. The 

 cause of the morning increase may be in operation every day ; 

 but its influence is sometimes increased, sometimes diminished, 

 and sometimes entirely masked, by other irregular intervening 

 forces. Observations on a single day, or continued for a few 

 days only, cannot therefore determine either the amoiuit of the 

 effect due to the regular cause, or its inequalities at different 

 seasons. For this, mean values, taken from a great number of 

 days, are required. The same is the case with those progress- 

 ive changes which take place in one direction for a very long 

 time ; these we call secular, because they require a long series of 

 years to amount to many degrees. Single observations, repeated 

 after an interval of only a few years, even though performed on 

 the same day, in the same month, and at the same hour, can 

 afford us no certain knowledge respecting them; but mean 

 numbers, obtained by continued observations, allow us to an- 

 ticipate, at the end of very few years, what it would otherwise 

 take many tens of years to fix with any considerable degree of 

 approximation. 



With this view, from the very commencement of the obsen^a- 

 tions to be performed at our Magnetic Observatory, I have in- 

 cluded amon"! them the dailv determination of the absolute de- 



