DIURNAL VARIATIONS FOR THE HORIZONTAL COMPONENT. xii 
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. 
Mean Positive Difference. Mean Negative Difference. Mean Difference. 
Nov. | Feb. | May. | Aug. Nov. | Feb. | May. | Aug. . | Feb. | May. | Aug. | 
| Dec. |. Mar. | June, | Sept. Year. - | Mar. | June, | Sept. . | Mar. | June,| Sept. | 
| Jan. | April.| July. | Oct. - | April.| July. | Oct. . |April.| July. | Oct. 
0-00 0-00 0-00 0-00 0-00 0-00 0-00 ; ; 0-00 ooo | 
0496 | 0650 | 0425 | 0538 0956 | 0417 | 0790 B 0774 | 0421 
0431 | 0702 | 0413 | 0512 1276 | 0421 | 0638 Z 5 0906 | 0417 
0568 | 0807 | 0385 | 0505 0385 | 0727 1141 | 0385 
0395 | 0567 | 0463 | 0415 |) | 38 | 0675 | 0539 0686 | 0468 
0392 | 0536 | 0410 | 0436 0532 | 0491 0627 | 0463 
0405 | 0583 | 0369 | 0487 0442 | 0812 2 | 0665 | 0402 
0416 | 0403 | 0414 | 0534 0439 | 0708 0427 | 0426 
0404 | 0451 | 0472 | 0527 0445 | 0684 0514 | 0458 
0475 | 0506 | 0606 0477 | 0820 0561 | 0491 
0529 | 0429 | 0573 0456 | 0700 0651 | 0442 
0503 | 0510 | 0546 0541 | 0873 0599 | 0525 
0506 | 0555 | 0554 59: 0512 | 0749 0577 | 0533 
0529 | 0544 | 0588 5) 0555 | 0637 De 0550 | 0549 
0492 | 0529 | 0608 0562 | 0550 | 0477 | 0545 
0528 | 0592 | 0607 0505 | 0684 0486 | 0545 
0692 | 0620 | 0723 3 | 0561 | 0591 5) 0540 | 0589 
0632 | 0592 | 0837 5) 0462 | 0606 552 | 0575 | 0545 
0611 | 0472/0591 0511 | 0484 0605 | 0491 
0552 | 0512 | 0456 0485 0574 | 0512 
0482 | 0480 | 0539 0607 0487 | 0451 
0527 | 0433 | 0540 0673 J 0595 | 0368 
0615 | 0426 | 0533 5 2 0707 0713 | 0388 
0591 | 0411 | 0465 0670 0715 | 0399 
0558 | 0400 | 0514 0771 0658 | 0420 
KF OOODNaupwnwnoreo 
_—a— 
1st, 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 — 
Nov. Dec. Jan. Feb. March, April. May, June, July. Aug. Sept. Oct. Year. 
Minimum, — 65 am. —7> aM. 2) XM. —3! am —5> am. 
Maximum, . 113% a.m. 33” pm. +3) pM. +4" pM. +42) p.m. 
Minimum, — 8) pie 72 PM. Bod ceaeeiades eneGemasay 
Maximum, + 63> Pm. +2) am. 
A maximum occurs in each quarter between 3" p.m. and 6? p.m., and the minimum occurs in each quarter 
between 25 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. 
P Nov. Dec. Jan. Feb. March, April. May, June, July. Aug. Sept. Oct. Year. 
Maximum, +113 p.m. +2) aM. +35 aM. +1135 p.m. + 27 am. 
Minimum, — 635 a.m. 62 a.m. 72 aM. — 33>am. — 65 a.m. 
Maximum, 10° a.m. 92 aM. +15 pM. +105 a.m. 102 a.m. 
Minimum, 2h PM. —2) pM. — 83" p.m. — 53° pM, — 22 px. 
A principal maximum occurs in each quarter betwixt 11 p.m. and 35 4.m.; a secondary or principal maximum 
occurs betwixt 9" 4m. and 14pm. The least values of the negative mean difference occurs about the same 
hours in summer as the greatest values occur in winter, namely, between 85 p.m. and midnight. 
MAG. AND MeT. ops. 1845 anv 1846. U 
