64 



GAUSS AND WEBER ON TERBESTKIAL MAGNETISM. 



blished, although, in the mean numbers for the single months, 

 in the fourth and eighth columns, ten months give a difference 

 in the same direction. 



By combining the forenoon and afternoon fluctuations we 

 obtain the following means : 



April .... 



May 



June , 



July 



August . . . 

 September 

 October. . . 

 November 

 December. 

 January . 

 February . 

 March . . . 



First 

 Year. 



108 

 176 

 139 

 173 

 224 

 167 

 152 

 133 

 160 

 160 

 130 

 114 



Second 

 Year. 



114 

 156 

 161 

 215 

 214 

 251 

 254 

 190 

 271 

 245 

 166 

 133 



Third 

 Year. 



237 

 245 

 208 

 270 

 289 

 185 

 229 

 235 

 120 

 146 

 148 

 312 



Mean. 



164 

 196 

 172 

 223 

 244 

 204 

 216 

 191 

 195 

 189 

 155 

 206 



Mean Values. 



According to the numbers of the fourth column somewhat 

 greater fluctuations occur in the months from July to December 

 than in the other six ; but the mean values 3' 33" and 3' 1" have 

 too small a difference to justify a conclusion that greater fluctua- 

 tions commonly prevail in that period of the year, especially as 

 the difference has been principally occasioned by an excess in 

 the single year 1835-1836. 



On the other hand, the inequality of the fluctuations in each 

 of the three years, in relation to one another, is very perceptible ; 

 the mean value for the third year being about half as large again 

 as that of the first year. The general mean, from all observations 

 hitherto made, 3' 18", might therefore be considerably changed 

 by a longer continuance of the observations. 



These are the results which may be drawn from the daily re- 

 gister kept hitherto. It is highly desirable that similar obsei-va- 

 tions should be made at several stations, and at some they have 

 recently commenced. If, as is done at Milan, the observations 



