MontTHLY VARIATIONS FOR THE HORIZONTAL COMPONENT. XXXV1l 
TABLE 29.—Diurnal Range of the Horizontal Component of Magnetic Force, with reference to the 
Moon’s Age and Declination. 
After 
Moon | 
Mean. | farthest || 1846. | Mean. 
North. 
0-00 : diet ds 
4710 | 27— 1 
4235 2— 5 
3127 6— 8 || 
2936 345 9—12 | 
3436 13—15 
3058 16—19 
3874 20—22 | 
4982 23—26 | 
Variation of the Diurnal Range of the Horizontal Component with reference to the Moon’s Age and De- 
clination.—Table 29 has been formed from-the Tables in former volumes, and the Tables pages 12 and 33 of 
this volume. 
67. The conclusions from Table 29 are :— 
1st, That the diurnal range of the horizontal component is greatest about the time of opposition, and 
least about the time of conjunction; in the mean of the 4 years the range varies little from the time that the 
moon is 6 days till it is 20 days old; it also varies little during the remaining half lunation, but the value for 
the former is considerably greater than for the latter. 
2d, In the mean of the 4 years the diurnal range is a maximum about 4 days after the moon has attained 
its greatest north declination; it is a minimum when the moon is farthest north. The means for 1844 and 
also for 1845 indicate a minimum, both when the moon was farthest north and when farthest south, with 
maxima during the intermediate periods ; this result seems to deserve the greatest value, agreeing as it does 
with the conclusion deducible from a comparison of the laws of mean values and ranges, namely, that the 
range of the horizontal component is a maximum when its mean value is least, and vice versa. 
TABLE 30.—Mean Difference of a Single Observation of the Horizontal Component of Magnetic 
Force from the Monthly Mean, at the corresponding Hour, with reference to the Moon’s Age and 
Declination. 
| After 
Moon’s Varia- Moon 
Age. || 1844. | 1845. | Mean. | tions, | farthest || 1844- 
| North. 
d. d. | 0:00 a 0-00 0:00 z 0°00" d. d. || 0°00 q 
14—16 || 0668 | 0498 | 0583 |+0018 | 27— 1 || 0533 
17—20 | 0682 | 0591 | 0636 ||+0071 | 2— 5 | 0655 
| 
21924 || 0441 | 0578 | 0509 |_-0056] 6— 8 | 
25—28 | 0484 | 0539 | 0511 ||—0054 | 9—12 || 03510 
29— 1 || 0539 | 0571 | 0555 ||—o010 | 13—15 | 
2— 5 | 0497 | 0568 | 0532 |~-0033 | 16—19 | 
6— 9 | 0605 | 0556 | 0580 |-+0015 | 20—22 | 
10—13 | 0731 | 0493 | 0612 | +0047 | 23—26 | 
u | | i 
i=) 
or 
~I 
o 
68. Variation of the Mean Difference of a Single Observation from the Monthly Mean for the corresponding 
Hour with reference to the Moons Age and Declination.—The results for two years 1844 and 1845 from Table 
XXXYV., 1844, p. 369, and Table XXIX., p. 16 of this volume, are given in Table 30. The conclusions from 
this Table, which are nearly the same as those from Table 29, are as follow :-— 
’ 1st, The departure of the horizontal component from its monthly mean value for the corresponding hour, 
1s greatest about the time of opposition, and least about the time of conjunction; the actual epochs are imme- 
