Diurnal Variations for the Horizontal 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 Horn" in each Year, as deduced 

 from all the Regular Observations. 



Mak. 

 Mean 



Mean Positive Difference. 



Mean Negative Difference. 



Mean Difference. 



Nov. 



Feb. 



May. 



Aug. 





Nov. 



Feb. 



May. 



Aug. 





Nov. 



Feb. 



May. 



Aug. 





Time. 



1 Dec. 



Mar. 



June, 



Sept. 



Year. 



Dec. 



Mar. 



June, 



Sept. 



Year. 



Dec. 



Mar. 



June, 



Sept. 



Year. 





Jan. 



April. 



July. 



Oct. 





Jan. 



April. 



July. 



Oct. 





Jan. 



April. 



July. 



Oct. 





h. m. 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-on 



0-00 



0-00 



12 12 



0496 



0650 



0425 



0538 



0531 



0863 



0956 



0417 



0790 



0733 



0630 



0774 



0421 



0640 



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 



1103 



1840 



0385 



0727 



0921 



0750 



1141 



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 



0483 



0755 



0532 



0491 



0565 



0435 



0627 



0463 



0462 



0497 



17 12 



0405 



0583 



0369 



0487 



0461 



0537 



0875 



0442 



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 



0484 



0503 



0510 



0546 



0513 



0629 



0740 



0541 



0873 



0680 



0547 



0599 



0525 



0672 



0585 



23 12 



0495 



0506 



0555 



0554 



0524 



0593 



0671 



0512 



0749 



0627 



0540 



0577 



0533 



0637 



0571 



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 



Is^, 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. 



Feb. March, April. 



May, June, July. 



Aug. Sept. Oct 



- e^ A.M. 



-7*^ A.M. 



- 2^ A.M. 



- 3^ A.M 



llll'A.M. 



3i'> P.M. 



+ 3^ P.M. 



+ 4** P.M. 



— 3^ P.M. 

 + 6^^ P.M. 



7^ P.M. 

 + 2^ A.M. 















Year. 



+ 4ihp. 



A.M. 



M. 



A maximum occurs in each quarter between 3^ p.m. and 6** p.m., and the minimum occurs in each quarter 

 betAveen 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. 



2c?, The average negative difference has the following epochs of maxima and minima. 



Maximum, 

 Minimum, 

 Maximmn, 

 Minimum, 



Nov. Dec. Jan. 



-flllhp.M. 



- 61^ A.M. 



10^ A.M. 



2^ P.M. 



Feb. March, April. 



+ 2^ A.M. 



6*^ A.M. 



9^ A.M. 



— 2^ P.M. 



May, June, July. 



+ 3'! A.M. 



7'' A.M. 



+ 1^ P.M. 



-Si'* P.M. 



Aug. Sept. Oct. 



P.M. 



- Si'^A.M. 

 + 10^ A.M. 



— 51'' P.M. 



Year. 

 + 2»'A.M. 



- e^^A-M. 

 lOh 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 l^ p.m. The least values of the negative mean difference occurs 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 



