DIURNAL VARIATIONS FOR THE VERTICAL COMPONENT OF MAGNETIC FORCE. li 
97. From Table 46 we conclude, 
1st, That the diurnal range of the vertical component is greatest immediately after opposition, and that 
it is least about conjunction ; there is the appearance of a secondary maximum at conjunction in three of the 
years, and in the means of all. 
2d, That the diurnal range is a minimum when the moon is farthest south, and also when it is farthest 
north, and that it is a maximum when the moon is north of the equator. 
TasLE 47.—Mean Difference of a Single Observation of the Vertical Component of Magnetic Force, 
from the Monthly Mean at the corresponding Hour, with reference to the Moon’s Age and 
Declination. 
After | 
Moon | Varia- 
farthest Mean. | tions, 
| 
| 0-00 
0159 ||—0016 
0191 ||+0016 
0171 || —0004 
0170 ||—0005 
0154 ||—0021 
0199 | +0024 
0165 ||—0010 
0188 |+0013 | 
| 
98. Variation of the Mean Difference of a Single Observation from the Monthly Mean for the corresponding 
Hour, with reference to the Moon's Age and Declination—Table 47 has been formed from Table 41, p. 386, 
1844, and Table XLII., p. 23, of this volume. The conclusions from Table 47 are nearly the same as those 
already made for the diurnal range, No. 97, they are as follow :— 
1st, The mean difference of an observation of the vertical component from the monthly mean for the 
corresponding hour is a maximum about the time of opposition, and a minimum before and after conjunction, 
a secondary maximum occurring at conjunction. 
2d, The mean difference is a minimum when the moon is farthest north, and also when farthest south, 
maxima occurring between these epochs. 
The differences of the results for the single years from those for the mean of both are not greater than 
might be expected in such an investigation ; the general agreement of the results, however, with those for the 
diurnal ranges deduced from four years’ observations is a confirmation of their accuracy. 
DIURNAL VARIATIONS FOR THE VERTICAL COMPONENT OF MAGNETIC FORCE. 
Diurnal Variation of the Vertical Component.—The following Table has been formed in the manner 
already described for the magnetic declination, No. 26; the means from which it has been formed will be 
found in the previous volumes, and in this volume, pages 20 and 37. 
99. The following are the approximate epochs of the maxima and minima in apparent time, as deduced 
from Table 48. 
Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 
h. m. h. m. h. m, h. m. h. m. h. m. Lh m. h. m. h. m. h. m. h m. h. m. 
Max. +7 5 +525 +510 +60 +6 0 +620 4520 +60+5 5 +4 0 +615 + 6 45 
Mine -14 0 -14 0 -14 0 -1215 —13 46 13 45 -1410 -1315 -1315 -—16 30 -—13 0 —-16 20 
Max. 20 15 21 0 19 50 20 0 20 30 20 40 22 0 2 
Min. 0 0 0 15 0 0 — 010 23 55 23 40 23 30 2 
The principal maximum occurs between 4" p.m. and 7} p.m. in each month of the year; it occurs earliest in 
February and March of the first six months of the year, and in October and September of the remaining 
months ; it occurs latest in January and December ; and later in June than in the immediately preceding and 
succeeding months. A minimum occurs between midnight and 4° a.m. throughout the year, which is the prin- 
cipal minimum excepting in June. 
Only one maximum and minimum occur in the diurnal variation for the four winter months, November to 
February ; in the other months a secondary minimum occurs about noon, which becomes more distinct the nearer 
the time is to the summer solstice, when that minimum is better marked than the other near midnight. 
MAG. AND MET. oBs. 1845 anv 1846. n 
