DiUENAL VAEIATIONS FOR THE HORIZONTAL COMPONENT, 



XXXIX 



and from October to September, the morning maximum becomes smaller in comparison with the afternoon 

 maximum ; and in May and August there are traces of the former which wholly disappear in June and July. 

 The forenoon minimum occurs earliest in August, and before 10*^ a.m. in the four months from June till Sep- 

 tember ; it occurs latest in November and December, and after lO^i a.m. in the seven months October till 

 April : the afternoon maximum occurs earliest for the first six months of the year, in February, and for the 

 last six months, in September ; it occurs latest in June and December. In order to destroy the smaller ir- 

 regularities, means for groups of months have been taken ; the same groups have been used as those already 

 adopted for the magnetic declination (No. 31). 



Table 32. — Diurnal Variations of the Horizontal Component of Magnetic Force for Different Periods, 



deduced from Table 31. 















Six Months. 





Mak. 

 Mean 

 Time. 



Dec. 

 Jan. 

 Feb. 



March. 

 April. 



May. 

 June. 



July. 



Aug. 



Sept. 

 Oct. 

 Nov. 



Sept. 



to 

 Feb. 



March 



to 

 Aug. 



Twelve 

 Months. 



h. ni. 



0-00 



0-00 



0-00 



O'OO 



0-00 



0-00 



O'OO 



0-00 



12 12 



- 0232 



+ 0062 



+ 0026 



+ 0212 



-0006 



-0119 



+ 0100 



-0010 



13 12 



-0260 



-0223 



-0110 



-0029 



+ 0056 



-0102 



-0121 



-0112 



14 12 



-0435 



-0574 



- 0234 



-0182 



-0063 



- 0249 



-0330 



-0290 



15 12 



-0174 



-0171 



-0314 



-0225 



+ 0148 



-0013 



-0237 



-0125 



16 12 



+ 0035 



-0138 



-0412 



-0312 



+ 0213 



+ 0124 



-0287 



-0082 



17 12 



+ 0255 



+ 0010 



-0477 



-0540 



+ 0254 



+ 0254 



-0336 



-0040 



18 12 



+ 0319 



+ 0091 



-0691 



-0690 



+ 0136 



+ 0227 



- 0430 



-0101 



19 12 



+ 0273 



-0201 



-1058 



-1146 



-0231 



+ 0021 



-0802 



-0390 



20 12 



+ 0084 



-0866 



-1603 



-1761 



-0747 



-0332 



-1410 



-0871 



21 12 



-0203 



-1373 



-1916 



-2152 



-1299 



-0751 



-1814 



-1283 



22 12 



-0420 



-1599 



-1977 



-2129 



-1428 



-0924 



-1902 



-1413 



23 12 



-0374 



-1429 



-1511 



-1589 



-1122 



-0748 



-1510 



-1129 



12 



-0229 



-0892 



-0784 



-0866 



-0566 



-0398 



-0847 



-0623 



1 12 



+ 0064 



-0159 



-0014 



-0052 



+ 0039 



+ 0051 



-0075 



-0012 



2 12 



+ 0241 



+ 0379 



+ 0562 



+ 0573 



+ 0337 



+ 0289 



+ 0505 



+ 0397 



3 12 



+ 0281 



+ 0782 



+ 0942 



+ 1197 



+ 0610 



+ 0445 



+ 0974 



+ 0709 



4 12 



+ 0281 



+ 099^ 



+ 1476 



+ 1456 



+ 0640 



+ 0460 



+ 1309 



+ 0884 



5 12 



+ 0231 



+ 1195 



+ 1751 



+ 1824 



+ 0746 



+ 0488 



+ 1590 



+ 1039 



6 12 



+ 0269 



+ 1121 



+ 1803 



+ 1819 



+ 0713 



+ 0491 



+ 1581 



+ 1036 



7 12 



+ 0203 



+ 0938 



+ 1769 



+ 1594 



+ 0565 



+ 0384 



+ 1434 



+ 0909 



8 12 



+ 0135 



+ 0737 



+ 1260 



+ 1231 



+ 0404 



+ 0269 



+ 1076 



+ 0673 



9 12 



+ 0019 



+ 0478 



+ 0776 



+ 0784 



+ 0286 



+ 0152 



+ 0679 



+ 0416 



10 12 



-0191 



+ 0430 



+ 0532 



+ 0597 



+ 0197 



+ 0003 



+ 0520 



+ 0261 



11 12 



-0168 



+ 0403 



+ 0197 



+ 0385 



+ 0110 



-0029 



+ 0328 



+ 0149 



70. The following are the approximate epochs of maxima and minima in appar-ent time from Table 32. 

 (See also Plate II.) 



Minimum, 

 Maximum, 

 Minimum, 

 Maximum, 



Dec. Jan. Feb. 

 101» 20m A.M. 

 4:^ 0™ P.M. 

 2^ 0" A.M. 

 6h 10"! A.M. 



Bfarch, April. 

 10"^ 10™ A.M. 

 5h 15m P.M. 

 2^ Om A.M. 

 5h 45m A.M. 



May, June. 



101^ 0™ A.M. 



6h 20m P.M. 



July, Aug. 



Q'^ 35™ A.M. 



5h 45m P.M. 



Sept. Oct. Nov. 



lO^" 0™ A.M. 



5h 50m P.M. 



2^ 0™ A.M. 

 5h 30™ A.M. 



From these means of groups, the forenoon minimum occurs earliest in July and August, and latest in 

 December to February ; the afternoon maximum occurs earliest in December to February, and latest in May 

 and June ; the morning maximum occurs earliest in September to November, and latest in the three months 

 thereafter ; the after-midnight minimum appears to occur genei'ally about 2^ a.m. 



The previous conclusions are obtained from the means of all the daily observations ; the following Table 

 contains means for the same groups of months, dedu.ced from the 10 days selected in each month of 1844 as 

 free from intermittent disturbance, and the 10 days similarly selected for each month of 1845. See Table 

 XXVIII., p. 362, 1844, and Table XXV., p. 14, of this volume. 



mag. and met. obs. 1845 and 1846. 



k 



