GAUSS AND WEBER ON TERRESTRIAL, MAGNETISM. 



61 



still but imperfectly, from the influence of the irregular anomalies ; 

 but they are evidently still charged with the secular change. In 

 order to eliminate this, its amount between the middle of each 

 month and the 1st of October must be apphed with the negative 

 sign for the first six months, and with the positive sign for the 

 last six months. Assuming the above determined value for the 

 twelve months, 3' 46""2, we obtain the following results. 



In these results we find as much regularity as could be ex- 

 pected from the observations of three yeai's only. The first 

 column shows how much the forenoon dechnation in each month 

 differs from the mean forenoon dechnation, and in the same way 

 the second column shows the difference of the afternoon dech- 

 nation in each month and the mean afternoon dechnation. It 

 must be i-ecoUected that the latter mean itself is 10' 23"'8 

 greater than the former mean. 



It appears remarkable that in all the twelve months the fore- 

 noon and afternoon declinations fluctuate about theii- mean values 

 in opposite directions. In the five winter months, fi'om October 

 to February, the forenoon declination is greater, and the after- 

 noon dechnation less, than their respective mean values; and 

 both circumstances tend, during this portion of the year, to 

 render the differences less than their mean amount. In the 

 other seven months exactly the opposite effect takes place. 

 Moreover, these opposite fluctuations are, upon an average, 

 nearly of equal magnitude ; the consequence of which is, that 

 they nearly destroy each other in the mean given in the last 

 column. This result may be thus stated in other words : the mean 



