GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



G3 



Mean Fluctuation of the Magnetic Declination during the three 

 years from 1834 to 1837. 



April 



May 



June 



July 



August 



September . . 



October 



November • . 

 December .... 

 January . . . . 

 February .... 

 March 



Mean 



I. 



74 

 192 

 172 

 21.3 

 264 

 162 

 116 



79 

 132 

 146 

 116 

 100 



157 



II. 



126 

 124 

 171 

 24.3 

 253 

 325 

 296 

 205 

 324 

 274 

 146 

 109 



229 



III. 



205 



277 

 1<)9 

 287 

 269 

 207 

 216 

 308 

 71 

 138 

 164 

 366 



238 



Mean. 



147 

 207 

 181 

 250 



262 

 241 



218 

 206 

 196 

 143 



909. 



211 



1, P.M. 



I. 



129 



158 



95 



119 



175 



172 

 182 

 170 

 184 

 174 

 178 

 127 



156 



II. 



101 

 183 

 151 

 184 

 165 

 143 

 202 

 173 

 206 

 212 

 183 

 153 



174 



III. 



264 

 210 

 217 

 252 

 307 

 161 

 242 

 126 

 154 

 154 

 129 

 246 



213 



Mean. 



180 

 185 

 162 

 193 

 225 

 159 

 210 

 158 

 182 

 181 

 165 

 183 



183 



In reference to the single observations, Ave may here mention 

 the greatest fluctuations which have occuitccI in the course of 

 thi'ee years, in the forenoon and afternoon declinations. The 

 greatest forenoon fluctuation was on the 8th of October, 1835, 

 when the declination was about 20' 1" greater than on the 7th of 

 October ; and the greatest afternoon fluctuation occurred on the 

 24th of April, 1836, when the declination was 13' 0" greater than 

 on the preceding day. On the other hand, perfect equaUty either 

 of the forenoon or of the afternoon declinations, for two successive 

 days, is a circumstance which has fi'equently occurred. In the 

 monthly mean fluctuations these extremes naturally come much 

 closer together ; nevertheless, the great dissimilarity of the single 

 months in this respect is still veiy remarkable, since, accorcHng 

 to the above general view, the mean fluctuation in the forenoon 

 decHnation in March, 1837, amounted to 6' 6"; in December, 

 1836, only to 1' 11". 



Whether, in general, greater fluctuations prevail at one time 

 of the day than at others, cannot be determined with certainty, 

 from the results of our observations of 8 a.m. and 1 p.m. Both 

 are nearly equal in mean fluctuation for the first year ; in the 

 two following years the forenoon fluctuations exceed in amount, 

 but the difference in the final results from the three years, 3' 31" 

 and 3' 3", is too small to allow of any conclusion bemg yet esta- 



