Vertical Component of Magnetic Eoece. 



243 



The mean at IS*^ in January is rendered comparable with the means at the other hours, thus : — 



Mic. Div. 

 Mean of balance magnetometer readings, January 9 — 31. = 768-8 



January 16—31. = 7645 



Diflerence, . . . , = 4-3 



The mean for IB'* deduced from the observations January 16 to 31 was therefore corrected by +4-3 

 micrometer divisions, in order to reduce it to the mean from January 9 to 31, as for the other hours. 



TABLE XVIII. — Diurnal Variations of the Vertical Component of Magnetic Force in 1843, the whole 



Vertical Component being Unity. 



Periods. 



IS". 



20>'. 



22'». 



231". 



Oh. 



21'. 



4''. 



6^. 



8i>. 



IC". 



Eange. 





0-00 



0-00 



O'OO 



0-00 



O'OO 



0-00 



0-00 



O'OO 



0-00 



0-00 



0-00 



January 



0000 



0059 



0087 





0111 



0119 



0105 



0166 



0189 



0168 



0189 



February 



0000 



0049 



0059 





0038 



0049 



0119 



0197 



0215 



0155 



0215 



March 



0004 



0060 



0079 





0013 



0000 



0078 



0206 



0256 



0134 



0256 



April 



0000 



0060 



0132 





0067 



0074 



0235 



0535 



0423 



0213 



0535 



May 



0094 



0158 



0136 





0010 



0000 



0142 



0228 



0272 



0072 



0272 



June 



0097 



0180 



0155 





0038 



0000 



0119 



0233 



0220 



0162 



0233 



July 



0000 



0078 



0112 





0043 



0087 



0184 



0230 



0260 



0133 



0260 



August 



0030 



0122 



0133 





0000 



0067 



0149 



0254 



0230 



0103 



0254 



September 



0000 



0158 



0208 





0107 



0166 



0230 



0271 



0169 



0045 



0271 



October 



0000 



0098 



0180 





0165 



0184 



0268 



0259 



0182 



0116 



0268 



November 



0000 



0026 



0073 



0052 



0063 



0127 



0176 



0142 



0151 



0126 



0176 



December 



0000 



0017 



0054 



0049 



0083 



0141 



0215 



0224 



0263 



0168 



0263 



Spring 



0000 



0055 



0089 





0038 



0040 



0143 



0312 



0297 



0166 



0312 



Summer 



0035 



OHO 



0105 





0001 



0000 



0119 



0201 



0222 



0093 



0222 



Autumn 



0000 



0116 



0167 





0081 



0129 



0206 



0251 



0184 



0078 



0251 



Winter 



0000 



0034 



0071 





0086 



0129 



0165 



0177 



0201 



0154 



0201 



Winter Solstice 



0000 



0038 



0068 





0074 



0109 



0154 



0182 



0204 



0154 



0204 



Equinoxes 



0000 



0093 



0149 





0087 



0105 



0202 



0317 



0257 



0126 



0317 



Summer Solstice 



0032 



0111 



0113 





0000 



0015 



0125 



0213 



0222 



0095 



0222 



The Year 



0000 



0070 



0100 





0043 



3066 



0149 



0227 



0217 



0114 



0227 



Diurnal Variation of the Vertical Component of Magnetic Force. 



An examination of the monthly means will shew, that they may be arranged into three very distinct groups, 

 namely, the months January, February, November, and December, about the winter solstice ; the months 

 March, April, September, and October, about the equinoxes ; and the months May, June, July, and August, 

 about the summer solstice. A consideration of the monthly means, however, will shew, that the diurnal curves 

 pass gradually from the type of the one group to that of the next following. 



In the means of the months about the winter solstice there is but one maximum and one minimum dis- 

 tinctly shewn ; the diurnal curve is single. 



The minimum occurs before 5^ 10™ a.m., Makerstoun mean time. 

 The maximum occurs between 6^ and 7^ p.m., 



There is a slight inflexion in the curve about 1 1 a.m., tending to a minimum ; this minimum is more or less 

 shewn in the separate monthly means, but never very distinctly excepting in February. 



In the mean of the months, about the equinoxes, there are two maxima and two minima shewn ; the diurnal 

 curve is double : — 



The minimum occurs between 9** p.m. and 5^ a.m., Makerstoun mean time. 



The maximum occurs at 5^* 10™ p.m., 



A secondary maximum occurs about 9** 10™ a.m., 



A secondary minimum ll'* 40™ a.m., 



