Monthly Vaeiations for the Horizontal Component. 
xxxvn 
Table 29. — Diurnal Range of the Horizontal Component of Magnetic Force, with reference to the 
Moon's Age and Declination. 
1 
Moons j 
Age. 
1 
18-i3. 
1844. 
1845. 
1846. 
Mean. 
After 
Moon 
fa/ftliest 
North. 
1843. 
1844. 
1845. 
1846. 
_ — . 
Mean. 
d. d. 
0-00 
O'OO 
I>00 
0-00 
0-00 
d. d. 
O'OO 
0-00 
0-00 
O'OO 
0-00 
14—16 
3105 
4710 
3683 
4906 
4101 
27— 1 
3527 
3267 
3686 
4209 
3672 
17—20 
2846 
4235 
3959 
5489 
4132 
2— 5 
3792 
4481 
4429 
4285 
4247 
21—24 
2504 
3127 
3685 
4634 
3487 
6— 8 
3031 
4115 
4019 
4197 
3840 
25—28 1 
3282 
2936 
2986 
4510 
3428 
9—12 
2907 
3401 
3615 
5377 
3825 
29— 1 
2771 
3436 
3920 
4434 
3640 
13—15 
2998 
3248 
3491 
5394 
3783 
2— 5 
2792 
3058 
4492 
4429 
3693 
16—19 
2634 
3546 
4712 
4080 
3743 
6— 9 
3792 
3874 
4076 
4729 
4118 
20—22 
2795 
3682 
3290 
5271 
3759 
10—13 ; 
3145 
4982 
3706 
4370 
4051 
23—26 
2665 
4311 
3137 
4620 
3683 
Variation of the Diurnal Mange of the Horizontal Component with reference to the 3Ioon's Ac/e 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 
mth 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 Diiference 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. 
Moon's 
Age. 
1844. 
1845. 
Mean . 
Varia- 
tions. 
After 
Moon 
farthest 
North. 
1844. 
1845. 
Mean. 
Varia- 
tions. 
d. d. 
0-00 
0-00 
O'OO 
0-00 
d. d. 
O'OO 
0-00 
0-00 
0-00 
14—16 
0668 
0498 
0583 
+ 0018 
27— 1 
0533 
0519 
0526 
-0036 
17—20 
0682 
0591 
0636 
+ 0071 
2— 5 
0655 
0643 
0649 
+ 0087 
21—24 
0441 
0578 
0509 
-0056 
6— 8 
0588 
0577 
0582 
+ 0020 
25—28 
0484 
0539 
0511 
-0054 
9—12 
0510 
0536 
0523 
-0039 
29— 1 
0539 
0571 
0555 
-0010 
13—15 
0519 
0484 
0501 
-0061 
2— 5 
0497 
0568 
0532 
- 0033 
16—19 
0560 
0647 
0603 
+ 0041 
6— 9 
0605 
0556 
0580 
+ 0015 
20—22 
0570 
0472 
0521 
-0041 
10—13 
0731 
0493 
0612 
+ 0047 
23—26 
0675 
1 
0507 
0591 
+ 0029 
68. Variation of the Mean Difference of a Single Observation from the Moyithly Mean for the corresponding 
Hour ivith reference to the Moon's Age and Declination. — The results for two years 1844 and 1845 from Table 
XXXV., 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 : — 
I \st. The departure of the horizontal component from its monthly mean value for the corresponding hour, 
I IS greatest about the time of opposition, and least about the time of conjunction ; the actual epochs are imme- 
