Vertical Component of Magnetic Force. 
245 
winter than in summer, as there is an indication of a minimum ahout 5 h a.m. The following are the results 
from the mean of hoth years : — 
The principal minimum at l h 10 m a.m., Makerstoun mean time. 
The principal maximum at 6 h p.m., 
A secondary maximum at 9 h 10 m a.m., 
A secondary minimum at ll h 40 m a.m., • 
The same results may be deduced from these means as have been already deduced from the means 
Table XVIII. 
Secular Change of the Vertical Component of Magnetic Force. 
The means for the year 1844 shew that the means of the observations at 22 h and 0 h , and at 4 h and 6 h , 
are respectively very nearly the same as the means of the observations at 23 h and 5 h . Assuming that they 
are equal for the year 1843, we shall have from the means for the year at the foot of Table XVIII. = 0-000100 
and from the mean for the year deduced from the means at the the foot of Table XV. = 0'015935. 
Mean at 20 h less than the mean of 9 observations from Table XVIII. by 0-000040, or = 0-015895 
Mean for 23 h " 0-000039, or = 0-015896 
Mean at 2 h 0-000044, or = 0-015891 
Mean for 5 h greater 0-000078, or = 0-016013 
From Table XVII., Abstracts for the observations of 1842, we have the means in micrometer divisions at 
the corresponding hours in 1842, these being converted into parts of force by the first formula given in the 
remarks to Table XV. we have, 
1842 ; 20 h = 0-017902, 23 h = 0-017962, 2 h = 0-017980, 5 h = 0-018147. 
The means above for 1843 being subtracted from these, we have — 
Secular change, 20 h = -0-002007, 23 h = -0-002066, 2 h = -0-002089, 5 h = -0-002134. 
Mean secular change 1842 to 1843, = -0-002074. 
Ranges of the Monthly Means of the Diurnal Variations. 
The ranges given in the last column of Table XVIII. must be very imperfect for some months, since the 
minimum actually occurs in general a little after midnight. It is very obvious, however, that the range is 
greatest at the equinoxes, and that it differs little in summer from winter, thus the diurnal range of the mean 
for the winter group of months is 0'000204, for the summer group 0*000222, while for the group at the 
equinoxes it is 0-000317- The corresponding groups in Table XIX. give the following ranges : — 
Diurnal range ; winter group = 0-000251 ; summer group = 0-000492 ; equinoctial group = 0-000788 ; 
or nearly in the ratios of 1, 2, and 3. 
TABLE XX. — Diurnal Ranges of the Vertical Component of Magnetic Force, as deduced from the 
9 Daily Observations in 1843, with the Weekly and Monthly Means. 
Civil 
Day. 
January. 
February. 
March. 
April. 
May. 
June. 
July. 
August. 
September. 
October. 
November. 
December. | 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
o-00 
O'OO 
0-00 1 
1 
[ ] 
0227 
0130 
0226 
0168 
0292 
0492 
0211 
[0481] 
0442 
0400 
2 
0959 
0099 
0111 
[0865] 
0258 
0414 
[0363] 
0297 
0421 
0213 
0468 
3 
0356 
0159 
0135 
0371 
0314 
0597 
0406 
0366 
[ ] 
0501 
0681 
[0270] 
4 
0056 
0162 
0474 
0332 
0338 
0405] 
0185 
1536 
0282 
0312 
0184 
5 
0096 
[0283] 
[0810] 
3738 
0200 
0469 
0238 
0288 
1011 
[0327] 
0286 
6 
0251 
0802 
0434 
0373 
2713 
0264 
0274 
[0798] 
0262 
0396 
0217 
0166 
7 
0267 
0355 
3300 
1416 
[0894] 
0398 
0300 
0266 
0436 
0228 
0303 
0247 
8 
[0360] 
0123 
0407 
1330 
0512 
0421 
0945 
0807 
0459 
[0341] 
0232 
1177 
9 
0610 
0280 
0322 
[0838] 
1010 
0139 
[0361] 
1526 
0542 
0139 
0373 
0555 
10 
0259 
0165 
0191 
0363 
0590 
0254 
0378 
0353 
[0459] 
0133 
0246 
[0633] 
11 
0676 
0276 
0163 
0434 
0185 
[0387] 
0140 
0399 
0418 
0141 
0105 
0822 j 
12 
0133 
[0351] 
[0347] 
1112 
0145 
0499 
0129 
0143 
0446 
0210 
[0264] 
0552 ! 
., 1 
mag. and met. obs. 1843 
