xl 
General Results of the Makerstoun Observations. 
Table 33. — Diurnal Variations of the Horizontal Component of Magnetic Force for Different 
Periods, deduced from Days selected as free from Irregular Disturbances, in the Years 1844 
and 1845. 
Mak. 
Dec. 
March. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Six Months. 
Twelve 
Months. 
Mean 
Jan. 
Feb. 
Oct. 
Sept. to 
Feb. 
March 
to Aug. 
li. m. 
19 T 5> 
0-00 
— 0098 
0-00 
+ 0283 
0-00 
+ 0244 
0-00 
+ 0287 
0-00 
4- m on 
0-00 
+ 0046 
0-00 
+ 0271 
0-00 
+ 0159 
— 0168 
4-0181 
— V/ J O i 
— 0018 
+ 0149 
— W L/U J 
14 12 
— 0158 
+ 0073 
— 0002 
+ 0044 
+ 0138 
— 0010 
+ 0038 
4- om 4 
15 12 
— 0066 
+ 0007 
— 0104 
+ 0002 
+ 0180 
+ 0057 
A A O O 
+ 0012 
16 12 
+ 0038 
+ 0034 
— n 1 'i9 
— 0072 
+ 0240 
+ Oloy 
A At: 0 
— (Judo 
+ 0037 
17 12 
+ 0176 
+ 0153 
— 0236 
+ 0279 
+ 0227 
A 1 O O 
— 0132 
+ 0047 
18 12 
+ 0206 
+ 0072 
— 0555 
— 0512 
+ 0151 
1 A 1 "7 O 
+ 0178 
AQ Q O 
— 0076 
19 12 
+ 0210 
— 0163 
— 0880 
— 0945 
— 0138 
T UUoo 
— UODO 
— 0313 
20 12 
+ 0057 
— 0687 
— 1 '^63 
— 15 14 
— 0734 
AO O O 
— 1 1 SO 
— 0763 
21 12 
— 0142 
— 1230 
— 1 723 
— 1908 
— 1217 
-0679 
- 1620 
— 1 149 
22 12 
— 0380 
— 1610 
— 1948 
— 1434 
-0907 
- 1791 
— 1 349 
23 12 
-0422 
- 1471 
- 1461 
- 1506 
- 1107 
-0764 
- 1479 
- 1122 
0 12 
— 0251 
— 1030 
— 0846 
— 0848 
— 0706 
-0478 
-0908 
— 0693 
1 12 
+ 0025 
-0464 
-0159 
-0116 
-0138 
-0056 
-0246 
-0152 
2 12 
+ 01.34 
+ 0019 
+ 0232 
+ 0472 
+ 0138 
+ 0136 
+ 0241 
+ 0188 
3 12 
+ 0115 
+ 0448 
+ 0681 
■f-0887 
+ 0303 
+ 0209 
+ 0672 
+ 0440 
4 12 
+ 0145 
+ 0488 
+ 0962 
+ 0898 
+ 0438 
+ 0291 
+ 0783 
+ 0536 
5 12 
+ 0236 
+ 0671 
+ 1321 
+ 1155 
+ 0485 
+ 0360 
+ 1049 
+ 0705 
6 12 
+ 0217 
+ 0796 
+ 1410 
+ 1241 
+ 0601 
+ 0409 
+ 1149 
+ 0779 
7 12 
+ 0120 
+ 0884 
+ 1368 
+ 1276 
+ 0573 
+ 0346 
+ 1176 
+ 0761 
8 12 
+ 0060 
+ 0735 
+ 1105 
+ 1129 
+ 0510 
+ 0285 
+ 0990 
+ 0637 
9 12 
-0024 
+ 0607 
+ 0873 
+ 0877 
+ 0459 
+ 0217 
+ 0786 
+ 0501 
10 12 
-0016 
+ 0665 
+ 0628 
+ 0660 
+ 0386 
+ 0185 
+ 0651 
+ 0418 
11 12 
-0016 
+ 0545 
+ 0450 
+ 0507 
+ 0277 
+ 0130 
+ 0501 
+ 0315 
71. The following are the approximate epochs in apparent time deduced from Table 33. (See also tiie 
dotted curves, Plate II.) 
Dec. Jan. Feb. March, April. May, June. July, Aug. Sept. Oct. Xov. 
Minimum, 10'^ 45™ a.m. 10^ 25™ a.m. 9^^ 55™ a.m. 9^ 50™ a.m. 10'* 10™ a.m. 
Maximum, 5'' 30™ p.m. 7^ 0™ p.m. 6^ 30™ p.m. 6^ 55™ p.m. 6^ 35™ p.m.- 
Minimum, l"* 30™ a.m. 3^ 20™ a.m. P 55™ .v.m. 
Maximum, 6'> 35™ a.m. 5"* 30™ a.m. 30™ a.m. 
A comparison of these epochs with those deduced from Table 32 will shew, that the effect of disturbance is 
to accelerate the epochs of the forenoon minimum and afternoon maximum, those of the latter being most 
affected. In the undisturbed diurnal variation the afternoon maximum occurs latest in Maixh and April, and 
in July and August. 
72. Diurnal Variation of the Effect of Disturbance on the Horizontal Component. — The following result is 
obtained upon the assumption, that intermittent disturbance which affects the hourly mean position does not 
affect the monthly mean of the 24 hoiu-s ; or, tliat the differences found No. 57, between the monthly means of 
the undisturbed days, and of all the days, is due to continuous and regular laws, which have little effect on the 
relative hourly positions ; it a])pears very probable from No. 58, that this assumption is not quite accurate, but 
that the negative quantities in the following Table are too small, and the positive ones too large : those 
for the summer months, however, must bo near the truth, as disturbance had little or no effect on the mean for 
that group : the error in the values for the other periods cannot affect the epochs of positive and negative 
maxima. 
