Diurnal Vaeiations foe the Magnetic Declination. 
XXI 
Table 12. — Diurnal Variations of "Westerly Declination for each Month, as deduced from the Regular 
Daily Observations made during the Four Years 1843 to 1846. 
Mak. 
Mean 
Time. 
1 
J an. 
-T eD. 
March. 
April. 
May. 
J une. 
Juiy. 
Aug. 
Sept. 
1 
Oct. 
jSfov. 
Dec. 
h. m. 
, 
, 
12 10 
0-96 
0-74 
0-26 
1-90 
1-90 
4-21 
2-35 
1-53 
1-57 
0-99 
1-22 
0-94 
13 10 
1-02 
1-82 
0-73 
1-08 
2-18 
4-00 
1-97 
1-55 
1-23 
1-19 
1-84 
1-00 
14 10 
0-91 
1-99 
1-56 
0-32 
2-77 
3-56 
1-67 
2-07 
1-48 
1-50 
3-09 
1-92 
15 10 
Ml 
2-16 
0-45 
0-88 
2-69 
3-01 
2-43 
1-69 
0-74 
2-54 
2-79 
2-41 
16 10 
1-49 
1-83 
0-54 
1-78 
2-11 
1-79 
1-61 
0-53 
1-13 
2-65 
2-36 
2-57 
17 10 
1-68 
1-78 
0-89 
1-05 
1-21 
0-68 
0-48 
0-30 
1-55 
2-89 
2-44 
213 
18 10 
2-46 
2-21 
1-19 
0-73 
0-22 
0-00 
0-24 
0-00 
2-13 
3-40 
2-57 
2-53 
19 10 
2-62 
2-51 
0-95 
000 
0-00 
0-32 
0-00 
0-12 
2-06 
3-00 
2-90 
2-47 
20 10 
2-54 
2-86 
0-68 
002 
1-31 
1-13 
1-04 
1-23 
3-01 
2-52 
3-01 
2-68 
21 10 
3-00 
3-50 
1-40 
1-70 
2-93 
3-11 
2-62 
2-85 
4-41 
349 
3-45 
2-81 
22 10 
4-00 
4-63 
3-43 
3-96 
5-70 
5-79 
5-02 
5-41 
6-82 
5-72 
4-92 
3-71 
23 10 
4-96 
6-23 
6-13 
7-37 
8-60 
8-92 
7-90 
8-32 
9-26 
8-07 
6-43 
4-94 
0 10 
5-53 
6-88 
8-18 
10-40 
10-33 
10-83 
9-82 
10-47 
10-45 
9-50 
7-55 
5-97 
1 10 
5-85 
7-11 
9-28 
11-29 
11-02 
11-61 
10-60 
10-83 
10-18 
9-41 
7-10 
6-02 
2 10 
4-89 
6-53 
8-02 
10-32 
10-30 
11-21 
9-76 
9-79 
8-89 
8-30 
6-44 
5-27 
3 10 
4-16 
5-03 
6-48 
8-44 
8-67 
9-80 
8-63 
7-36 
6-54 
6-65 
5-20 
4-03 
4 10 
3-76 
4-08 
4-77 
6-57 
'TIT 
7-17 
8-05 
7-14 
5-59 
4-34 
4-65 
4-28 
3-48 
5 10 
2-69 
3-31 
2-37 
4-24 
5-65 
6-45 
6-08 
3-77 
3-28 
3-43 
3-63 
2-77 
6 10 
1-97 
2-28 
1-31 
282 
4-98 
5-53 
4-97 
2-03 
1-87 
2-71 
1-96 
1-89 
7 10 
1-55 
1-88 
1-39 
1-76 
4-21 
5-26 
4-08 
2-28 
0-69 
2-39 
1-38 
1-41 
8 10 
0-83 
0-70 
0-77 
1-56 
3-32 
5-02 
3-45 
2-30 
0-00 
0-64 
0-48 
0-01 
9 10 
0-28 
0-32 
0-27 
1-52 
3-30 
4-65 
2-80 
1-54 
0-68 
0-74 
0-18 
0-29 
10 10 
0-36 
0-00 
0-51 
1-51 
3-'l4 
4-38 
2-57 
1-38 
0-95 
0-29 
0-00 
0-23 
11 10 
0-00 
0-89 
0-00 
Ml 
2-42 
4-04 
2-29 
1-81 
0-94 
0-00 
0-30 
0-00 
28. From Table 12 we find that the north end of the declination magnet is most westerly throughout the year 
between 0^ 20™ p.m., and l'^ 25™ p.m., the epochs in apparent time for each month being as follow : — 
Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 
Qh 50m 0*^ 50™ 0^ 55™ 10™ 1"^ 15™ P 25™ l^* 0™ O*' 50™ 0^ 30™ O^^ 45™ 0^ 35™ O^^ 50™ 
It appears, therefore, that the maximum westerly declination occurs farthest after apparent noon in the months 
of April, May, and June ; and that it occurs soonest after apparent noon in September, October, and Novem- 
ber. 
29. The north end of the declination magnet is most easterly from April to August, from 6'^ to 8^^ in the 
morning, and from September to March from S** to 11 in the evening: the approximate epochs in apparent 
time are as follow : — 
Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 
lOh 50m 9h 45m iQh iQh 40™ 181^ 50™ 18^ 20™ 5™ 18*^ 25™ 8^ 10™ 11^ 10™ 10^^ 20™ 9^ 50™ 
30. These epochs are considerably less certain than those for the maximum, especially when they occur be- 
tween 9*^ 10™ and 17"^ 10™, as they depend upon only two years' observations. The principal minimum occurs 
between 8^ and 11'' p.m. in the months from September till March, in the latter month the westerly declina- 
tion at 8^ A.M. differs little from that at ll'' p.m. : in the remaining months the minimum occurs between 
20™ and 7^ 40™ a.m. The morning minimum occurs earliest in J une and August ; the evening minimum 
occurs earliest in September. 
31. Secondary maxima and minima of westerly declination are shewn with moderate distinctness in some 
months, but the epochs vary so much from one month to the next as to render it doubtful whether they are other- 
wise than accidental : clearer results may be expected from the combinations of the means for two or three 
months, if sufficient care be taken that only those months are combined which exhibit separately similar cha- 
racteristics. A careful examination of the projected means, seems to shew the combinations employed for the 
following Table, as those best fitted for exhibiting distinctly the changmg character of the diurnal variation. 
