Vertical Component of Magnetic Force. 
243 
The mean at 18 h 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. = 764-5 
Difference, = 4-3 
The mean for 18 h 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. 
18\ 
20*. 
22 h . 
23 h . 
0\ 
2 b . 
4*. 
6>>. 
8 h . 
10 h . 
1 Range. 
0-00 
0-00 
0-00 
o-oo 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
January 
0000 
0059 
00S7 
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 
0110 
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 
0066 
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 h 10™ a.m., Malcerstoun mean time. 
The maximum occurs between 6 h and 7 h p.m., 
There is a slight inflexion in the curve about 11 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 h p.m. and 5 h a.m., Makerstoun mean time. 
The maximum occurs at 5 h 10 m p.m., 
A secondary maximum occurs about 9 h 10 m a.m., 
A secondary minimum ll h 40 m a.m., 
