DiUENAL VaEIATIONS FOE THE HOEIZONTAL COMPONENT. 
xliii 
Table 36. — Mean Difference of the Observations of the Horizontal Component of Magnetic Force, 
in 1844 and 1845, from the Monthly Means, at the corresponding Hour in each Year, as deduced 
from all the Regular Observations. 
Mak. 
Mean 
Time. 
Mean Positive Difference. 
Mean Negative Difference. 
Jlean Difference. 
, Nov. 
i Dec. 
Jan. 
Feb. 
Mar. 
April. 
May. 
June, 
July. 
Aug. 
Sept. 
Oct. 
Year. 
Nov. 
Dec. 
Jan. 
Feb. 
Mar. 
April. 
May. 
June, 
July. 
Aug. 
Sept. 
Oct. 
Year. 
Nov. 
Dec. 
Jan. 
Feb. 
Mar. 
April. 
May. 
June, 
July. 
Aug. 
Sept. 
Oct. 
Year. 
h. 
12 
m. 
12 
O'OO 
0496 
O'OO 
0650 
O'OO 
0425 
O'OO 
0538 
O'OO 
0531 
O'OO 
0863 
O'OO 
0956 
O'OO 
0417 
O'OO 
0790 
O'OO 
0733 
O'OO 
0630 

O'OO 
0774 
O'OO 
0421 
'- 
O'OO 
0640 
ti'UO 
0616 
13 
12 
0431 
0702 
0413 
0512 
0522 
0704 
1276 
0421 
0638 
0721 
0535 
0906 
0417 
0568 
0606 
14 
12 
0568 
0807 
0385 
0505 
0589 
1 103 
1840 
0385 
0727 
0921 
0750 
1 141 
0385 
0596 
0718 
15 
12 
0395 
0567 
0463 
0415 
0461 
0618 
0868 
0675 
0539 
0612 
0482 
0686 
0468 
0469 
0526 
16 
12 
0392 
0536 
0410 
0436 
0444 
0489 
0755 
0532 
0491 
0565 
0435 
0627 
0463 
0462 
0497 
17 
12 
0405 
0583 
0369 
0487 
0461 
0537 
0875 
0142 
0812 
0637 
0462 
0665 
0402 
0609 
0535 
18 
12 
0416 
0403 
0414 
0534 
0443 
0424 
0454 
0439 
0708 
0500 
0420 
0427 
0426 
0609 
0470 
19 
12 
0404 
0451 
0472 
0527 
0464 
0437 
0598 
0445 
0684 
0534 
0420 
0514 
0458 
0595 
0497 
20 
12 
0425 
0475 
0506 
0606 
0502 
0460 
0684 
0477 
0820 
0601 
0442 
0561 
0491 
0697 
0547 
21 
12 
0482 
0529 
0429 
0573 
0504 
0601 
0845 
0456 
0700 
0641 
0535 
0651 
0442 
0630 
0564 
22 
12 
1 0484 
0503 
0510 
0546 
0513 
0629 
0740 
0541 
0873 
0680 
0547 
0599 
0525 
0672 
0585 
23 
12 
yj Ooo 
yjKj t 1 
Ot 1 9 
0740 
UDyrU 
y)o i i 
Ci^l 1 
UO / 1 
0 
12 
0513 
0529 
0544 
0588 
0547 
0567 
0573 
0555 
0637 
0580 
0539 
0550 
0549 
0612 
0563 
1 
12 
0459 
0492 
0529 
0608 
0521 
0507 
0463 
0562 
0550 
0521 
0482 
0477 
0545 
0578 
0521 
2 
12 
0422 
0528 
0592 
0607 
0530 
0526 
0450 
0505 
0684 
0540 
0468 
0486 
0545 
0643 
0535 
3 
12 
0401 
0692 
0620 
0723 
0591 
0500 
0443 
0561 
0591 
0525 
0445 
0540 
0589 
0651 
0556 
4 
12 
0435 
0632 
0592 
0837 
0606 
0756 
0528 
0462 
0606 
0582 
0552 
0575 
0545 
0703 
0594 
5 
12 
0488 
0611 
0472 
0591 
0536 
0660 
0599 
0511 
0484 
0558 
0561 
0605 
0491 
0532 
0547 
6 
12 
0794 
0552 
0512 
0456 
0592 
0733 
0598 
0512 
0485 
0569 
0762 
0574 
0512 
0470 
0580 
7 
12 
0600 
0482 
0480 
0539 
0530 
0881 
0492 
0425 
0607 
0585 
0714 
0487 
0451 
0571 
0556 
8 
12 
0568 
0527 
0433 
0540 
0521 
0708 
0684 
0320 
0673 
0576 
0630 
0595 
0368 
0599 
0547 
9 
12 
0607 
0615 
0426 
0533 
0553 
0838 
0849 
0356 
0707 
0663 
0704 
0713 
0388 
0608 
0603 
10 
12 
0541 
0591 
0411 
0465 
0505 
1004 
0905 
0387 
0670 
0712 
0703 
0715 
0399 
0549 
0591 
11 
12 
0559 
0558 
0400 
0514 
0508 
0821 
0914 
0442 
0771 
0701 
0665 
0658 
0420 
0617 
0589 
The average positive difference of an observation of the horizontal component has its maximum and 
minimum values at the following hours in the means of the four quarters, the times of the principle values being 
distinguished by + and — 
Minimum, 
Maximum, 
Minimum, 
Maximum, 
Nov. Dec. Jan. 
- 6^ A.M. 
11^^ A.M. 
- S''^ P.M. 
+ 6^1i P.M. 
Feb. March, April. 
— 7'' A.M. 
P.M. 
1^ P.M. 
+ 2*^ A.M. 
May, June, July. 
-2^ A.M. 
+ P.M. 
Aug. Sept. Oct. 
- 3^ A.M 
+ 4*^ P.M. 
Year. 
— 5^ A.M. 
+ P.M. 
A maximum occurs in each quarter between 3^ p.m. and 6'^ p.m., and the minimum occurs in each quarter 
between 2^ a.m. and 6^ a.m. ; there are, however, several points of opposition : thus, the principal minimum 
in summer and autumn occurs at the hour of the principal maximum in spring ; and one of the two equally- 
marked minima of winter occurs at the same hour as the principal maximum in summer and autumn, and as 
the well-marked secondary maximum in spring. 
2d, The average negative difference has the following epochs of maxima and minima. 
Maximum, 
Minimum, 
Maximum, 
Minimum, 
Nov. Dec. Jan. 
+ 111'^ P.M. 
- A.M. 
10^" A.M. 
2^ P.M. 
Feb. March, April. 
+ 2^ A.M. 
6^ A.M. 
9^ A.M. 
-2^ P.M. 
May, .rune, July. 
+ 3h A.M. 
1^ A.M. 
-f 1^ P.M. 
- 8^^ P.M. 
Aug. Sept. Oct. 
+ 1W' P.M. 
- H^A.M. 
+ 10^ A.M. 
- 51'> P.M. 
Year. 
+ 2^ A.M. 
- 6^ A.M. 
10^ A.M. 
- 2'^ P.M. 
A principal maximum occurs in each quarter betwixt 1 1'* p.m. and 3^^ a.m. ; a secondary or principal maximum 
occurs betwixt 9** a.m. and 1^ p.m. The least values of the negative mean difference occiu-s about the same 
hours in summer as the greatest values occur in winter, namely, between 8^ p.m. and midnight. 
MAG. AND MET. OBS. 1845 AND 1846. I 
