ON THE EARTH’S MAGNETISM. 
381 
Table II. — Showing the Monthly Aggregates of Disturbances of Horizontal Force 
exceeding ‘00334 (metre-gramme-second) units of force, from January 1847 to 
December 1872. 
Years. 
Disturbances 
increasing 
: the Horizontal Force. 
January. 
Febru- 
ary. 
March. 
April. 
May. 
June. 
July. 
August. 
Sep- 
tember. 
October. 
No- 
vember. 
1 De- 
cember- 
1847. 
•00907 
■01775 
•01674 
•02732 
•00000 
•00000 
•00000 
■04421 
•01062 
•08554 
•01976 
•02142 
1848. 
•03658 
■06152 
•02606 
•03002 
•02851 
•00000 
•05591 
•05134 
•00000 
•14069 
•03931 
•00000 
1849. 
•15325 
•01714 
•01512 
•00709 
•01523 
•02326 
■00745 
■01570 
•02459 
•02833 
•00659 
•00418 
1850. 
•01577 
•01544 
•01105 
•00000 
•01620 
•01951 
•02412 
•00000 
•00727 
•04946 
•00364 
•00796 
1851. 
•02077 
•02365 
•04298 
■00000 
•04550 
•05728 
■00349 
•01577 
•04406 
•04360 
•00000 
■00749 
1852. 
•04536 
•24419 
•11981 
•01501 
•03380 
•01076 
06502 
•01202 
•00403 
•10634 
•00832 
•02668 
. 1853. 
•02796 
•04004 
•03449 
•00369 
•04307 
•06008 
•09990 
•02997 
•04000 
■01945 
■00431 
•04752 
| 1854. 
■00409 
■00756 
•02712 
■03405 
•07026 
■00000 
■01132 
•01723 
•01548 
•00708 
•00000 
•00701 
1855. 
•00000 
■01460 
•00748 
•00000 
•01445 
■00000 
•04876 
■00000 
•00000 
■00339 
•00361 
•01106 
1856. 
•19274 
•02631 
•00000 
•00389 
•00349 
•01745 
■00000 
•00763 
•00348 
■00393 
•00000 
•00768 
1857. 
•00000 
•00000 
■00788 
•01888 
■02353 
•01179 
•01651 
•00000 
•07689 
•01406 
•04776 
•01950 
j 1858. 
•06034 
•03265 
■10996 
•04717 
•09666 
■06326 
•02741 
•00000 
04577 
•07583 
•03001 
•00974 
1859. 
•07124 
•02244 
•06345 
•09157 
•02721 
■03326 
■03232 
•04560 
■13183 
■22485 
•08819 
■02266 
1860. 
•05302 
•03254 
•19500 
•14087 
•05049 
■06765 
•07483 
•12618 
•13884 
•03510 
■01262 
•01841 
1861. 
•08372 
•10390 
•02560 
•03140 
•02096 
■19531 
•03583 
•05782 
■01107 
•03264 
■09290 
•03801 
1862. 
■06612 
■09045 
•00368 
•02728 
•04650 
•03443 
■08801 
•10445 
•10420 
•08087 
•00769 
■05626 
| 1863. 
•08151 
■10808 
•10098 
•09064 
•02881 
•12260 
•02140 
•20006 
•05847 
•03759 
•03886 
01101 
I 1864. 
•00372 
■02653 
•01799 
•06810 
•04201 
•13497 
•08710 
•03553 
•04273 
■06378 
•00788 
•00000 
1S65. 
•07666 
•07456 
■03871 
•00721 
•00338 
■01185 
•04881 
•23497 
•09785 
•18215 
•27939 
•03966 
1866. 
•03058 
•15329 
•14081 
•00829 
■00746 
•00000 
•05271 
•00382 
•02139 
•15274 
•02206 
■00685 
1867. 
•00492 
•00768 
•03120 
•04817 
■03156 
•00752 
•01156 
■00730 
•02848 
•11074 
■03429 
•03356 
1868. 
■01109 
■01866 
•00729 
■13932 
•00364 
•03920 
•02604 
■07877 
•11978 
•02688 
■00000 
•00000 
1869. 
•04751 
•04613 
■03694 
•16159 
•06674 
■11497 
•06630 
•06377 
•10358 
•02430 
•07031 
•03387 
1870. 
•09332 
■07691 
•08896 
•03309 
•04273 
■03987 
■04036 
•13553 
•18851 
•09500 
•25815 
•09626 
1871. 
•17428 
■01968 
•16671 
•29371 
■02320 
■12342 
•10727 
•08968 
•03199 
•04688 
•14534 
-08743 
1872. 
•08526 
•06741 
■04145 
•06270 
•07961 
•09175 
•06115 
■05030 
•09116 
•15568 
•20619 
■01625 
Disturbances decreasing the Horizontal Force. 
1847. 
•13291 
■07978 
•33491 
•47664 
■41126 
•01228 
•03791 
•24646 
1-29535 
•83941 
-62093 
1-32156 
1848. 
■41396 
•73566 
•52963 
■44082 
•25848 
•00839 
•42689 
•04676 
■14562 
1-03536 
1-31195 
•14882 
1849. 
•15361 
■34546 
07406 
•04392 
■06023 
■11311 
■02902 
•01472 
■09302 
•15531 
•42311 
•04392 
1850. 
05317 
■12276 
•06599 
■02308 
•04435 
■07866 
•11441 
•02045 
•04442 
■22712 
•01508 
•08766 
1851. 
•50339 
•21535 
•06455 
■00000 
■18515 
•14645 
•06707 
■08168 
1-34014 
•60210 
•06286 
•29423 
1 1852. 
•35381 
1 05696 
•11290 
•41404 
•12053 
•19390 
•11268 
•02830 
•28188 
•11441 
•14018 
•08564 
1853. 
•04322 
■20955 
•15304 
■28258 
•44698 
•14385 
•28554 
•00369 
•68770 
■02894 
■16352 
■38029 
1854. 
■20900 
•15717 
•33748 
•42278 
•11508 
•03705 
•08220 
01891 
•09457 
•26276 
•06979 
•04745 
1855. 
01555 
■05654 
•08636 
•10479 
■08041 
•02081 
•07373 
•02464 
•01256 
•25156 
•00369 
•02274 
1856. 
01195 
•05033 
•05268 
•03507 
•04994 
•00866 
•01681 
•09126 
•06655 
•10662 
•00917 
•12140 
; 1857. 
•00749 
■02415 
•00839 
•10126 
•47028 
•04741 
•02716 
•00816 
•24404 
•05347 
•35977 
1-24577 
1 1858. 
•42793 
•16029 
•58995 
•99566 
■19593 
•43089 
•07337 
•02714 
■35608 
•20237 
•14029 
•32211 
j 1859. 
•13537 
•89391 
•11752 
•62330 
■18915 
•30410 
•44571 
•46413 
1 12879 
1-77052 
•46265 
•82666 
1 1860. 
•10656 
■38462 
1 09309 
•38132 
•31114 
■08680 
•94931 
1-00879 
•43830 
•67307 
•21485 
•33536 
' 1861. 
•56006 
•29277 
•31021 
•21158 
•05457 
•05590 
•04264 
•17087 
•25154 
•59525 
•29297 
■63135 
1862. 
•24050 
•23634 
■29742 
•23392 
•10651 
■00891 
•18965 
•56125 
•43924 
•88875 
•25039 
•59343 
1863. 
•25914 
07879 
•07900 
•14163 
•11356 
■10037 
•19459 
•13433 
•30873 
•34188 
■11432 
•02252 
1864. 
•00339 
•06082 
■29916 
•22083 
•16067 
■63418 
•30811 
•31811 
•29252 
•20128 
•09667 
•02541 
1865. 
•26233 
•27368 
•14320 
•29201 
•19018 
■12277 
•07451 
•81050 
•09827 
•30819 
•33401 
■02432 
1866. 
•06729 
•90626 
•13067 
•07426 
•07078 
•01029 
•01222 
•20720 
•11476 
•29021 
•13876 
•09057 
1867. 
■04851 
•25234 
-05092 
■07295 
•12774 
■04279 
•04308 
•01123 
•13665 
•17425 
•08676 
■02294 
1868. 
•00000 
■08876 
■50612 
•35348 
•15057 
•09218 
•32487 
•15639 
■34444 
•54636 
•00000 
•01414 
1869. 
•27997 
•44794 
•34134 
■61314 
•77931 
•38806 
•06795 
■46084 
•55401 
•29192 
•21115 
•26690 
1870. 
•73891 
•51550 
■47810 
•48246 
•64513 
•35981 
•21999 
•67844 
1-28971 
109525 
•52101 
•57811 
1S71. 
•36799 
112210 
•51099 
•72576 
•05740 
•27627 
•33183 
•44565 
•31528 
•37913 
•73249 
•04426 
1872. 
•05184 
■96353 
•15542 
■92697 
•21553 
■27526 
■51272 
•94517 
•53956 
1-63515 
•17688 
•15274 
17. The sidereal .periods of revolution of Mercury, Venus, and the Earth are 87‘97, 
224-70, and 365*26 mean solar days respectively. Nine periods of Mercury are so 
nearly equal to 2^ years (26 months) that the accumulated difference after ninety-nine 
periods is less than four days, or of one period of Mercury ; and the time of thirteen 
periods of Venus differs from 8 years so little that after thirty-nine periods the accumu 
