Horizontal Component of Magnetic Force. 



361 



TABLE XXVII. — Diurnal Variations of the Horizontal Component of Magnetic Force in 1844. 



Mak. 

 M. T. 



.Lin. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Year. 



h. 



o-uo 



0-00 



0-00 



o-'oo 



(1-00 



0-00 



o-on 



000 



o-oo 



0-00 



O'OO 



0-00 



0-00 



12 



0167 



0458 



1176 



1796 



1634 



1947 



2260 



2052 



2190 



1785 



0556 



0150 



1327 



13 



0167 



0220 



0469 



2003 



1604 



1806 



2153 



1837 



2229 



1697 



0566 



0293 



1233 



14 



0088 



0118 



0591 



1758 



1457 



1704 



2017 



1789 



1961 



1667 



0528 



0105 



1128 



15 



0262 



0213 



0923 



1365 



1296 



1637 



1891 



1733 



2138 



1940 



0778 



0183 



1176 



16 



0427 



0228 



1106 



1662 



1119 



1469 



1785 



1779 



2150 



1859 



0931 



0477 



1229 



17 



0616 



0714 



0868 



1851 



1343 



1425 



1670 



1478 



2276 



1749 



0997 



0620 



1280 



18 



0622 



0580 



1532 



1712 



1197 



1054 



1537 



1417 



1950 



1663 



1210 



0750 



1248 



19 



0622 



0585 



1257 



1229 



0907 



0822 



1126 



0851 



1319 



1571 



1100 



0760 



0992 



20 



0456 



0601 



0652 



0479 



0357 



0333 



0676 



0144 



0946 



0855 



0913 



0515 



0557 



21 



0315 



0319 



0216 



0000 



0106 



0000 



0125 



0000 



0393 



0270 



0328 



0262 



0174 



22 



0000 



0126 



0000 



0064 



0000 



0001 



0000 



0056 



0000 



0000 



0000 



0000 



0000 



23 



0045 



0000 



0263 



0220 



0347 



0420 



0470 



0678 



0573 



0529 



0018 



0038 



0279 







0190 



0270 



0575 



1152 



1082 



1158 



1273 



1253 



1130 



1149 



0651 



0220 



0821 



1 



0498 



0622 



1432 



1666 



1508 



1711 



1992 



2124 



1949 



1627 



0686 



0309 



1323 



2 



0690 



0875 



1561 



2178 



2065 



2297 



2531 



2617 



2324 



1862 



0895 



0449 



1675 



3 



0517 



0799 



1998 



2541 



2261 



2528 



2884 



2992 



2440 



2254 



0934 



0501 



1867 



4 



0659 



0706 



2155 



2715 



3191 



2821 



3100 



2964 



2948 



2254 



0770 



0496 



2044 



5 



0550 



0557 



2195 



3378 



3427 



3060 



3282 



3501 



2769 



2313 



1305 



0452 



2212 



6 



0385 



0596 



1810 



3268 



3644 



3135 



3657 



3356 



2789 



2073 



1180 



0461 



2176 



7 



0192 



0547 



2192 



2839 



3454 



3179 



3626 



3296 



2779 



1994 



0770 



0393 



2084 



8 



0427 



0694 



2135 



2726 



3007 



2916 



3109 



3063 



2703 



2033 



0879 



0619 



2005 



9 



0322 



0592 



1259 



2376 



2554 



2631 



2785 



2591 



2719 



1903 



0568 



0235 



1691 



10 



0291 



0213 



1077 



2598 



2290 



2454 



2590 



2589 



2604 



1994 



0591 



0139 



1599 



11 



0298 



0134 



1526 



2142 



1855 



2061 



2393 



2061 



2493 



1764 



0424 



0234 



1428 



Diurnal Variation of the Horizontal Component. — The following is the mean result for the year 1844 : — 

 The horizontal component is a minimum at 10 h 10™ a.m., after which hour it increases with its greatest 

 rapidity, attaining its principal maximum at 5 h 30 m p.m. ; it then hegins to diminish, and continues to do so 

 with considerable regularity till 2 h 10 m a.m., when there is a secondary minimum; it again increases slightly, 

 and hecomes a secondary maximum at 5 h 30 m a.m., after which it diminishes with its greatest rapidity to the 

 principal minimum at 10 h 10 m a.m. The range of the mean diurnal variation is rather more than two thou- 

 sandths of the whole horizontal component (0-0022). An examination of the monthly means will shew, that 

 the two maxima and the two minima are each of nearly equal value in the winter months, the morning 

 maximum being the principal maximum in the month of December ; in the summer months, on the contrary, 

 the secondary maximum and minimum nearly or altogether disappear. There are several irregularities, 

 especially in the autumnal and winter months, which are evidently due to disturbances. The following are 

 the approximate times of the principal minimum (— ) and maximum ( + ), and of the secondary minimum 

 and maximum : — 







Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



-Min. 



A.M. 



10*20™ 



ll h m 



10 h 10 m 



9 h 30 m 



10 h 10™ 



9 h 40 m 



10 h m 



9 h 30 m 



10 h 10 m 



9 h 50 m 



10 h 30 m 



10 h 30 n 



+ Max. 



P.M. 



310 



2-10 



6-10 



5-20 



610 



7-0 



6-40 



5-10 



4-10 



50 



510 



3-20 



Min. 



A.M. 



2 



1 



1 



3 



4 







3 



2 



1-30 



11 P.M. 



1 A.M. 



Max. 



A.M. 



6-10 



6 



6 



5 



5 







4 



5 



3 



6-10 



6-40 



On the whole, it appears that the principal minimum occurs rather earlier in the day in the summer 

 months than in the winter months, and that the principal or afternoon maximum occurs rather later in the 

 day in the former than in the latter. 



In order to examine the diurnal variation when freed, as far as possible, from the effects of irregular 

 causes, the hourly observations on the days previously selected, Table VII., have been used. The following 

 Tables contain diurnal variations for the ten days and for the five days in each month least affected by 

 disturbances. 



MAG. AND MET. OBS. 1844. 



4y 



