DiuENAL Variations for the Magnetic Declination. 



xxm 



(Makerstoun Observations for 1844, p. 339) for the determination of this question; namely, by the selection of 

 those days in each month which appear to have been nearly unaffected by irregular disturbance ; a method 

 which it is conceived is considerably preferable to that of rejecting only those days affected with large magnetic 

 irregularity. The variations for ten days in each month of 1844 will be found p. 339 in the volume for that 

 year, and for seven days in each month of 1845, p. 5 of the present volume ; from these two Tables the follow- 

 ing Table has been formed : — 



Table 14. — Diurnal Variations of Westerly Declination for different periods, deduced from Days 

 selected as free from irregular disturbance, in the Years 1844 and 1845. 













CI i 



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. m. 



/ 



, 



/ 



/ 



, 



/ 



/ 



/ 



12 10 



-0-72 



-1-27 



-0-78 



-M3 



-113 



-0-92 



-106 



-0-99 



13 10 



-0-55 



-1-28 



-0-86 



-1-35 



-1-09 



-0-82 



-M6 



-0-99 



14 10 



-0-50 



-1-47 



-MO 



-1-40 



-106 



-0-78 



-1-32 



-1-05 



15 10 



-0-54 



-1-83 



-1-50 



-1-78 



-M7 



-0-85 



-1-70 



-1-28 



16 10 



-0-70 



-1-91 



-2-54 



-2-58 



-1-24 



-0-97 



-2-34 



-1-66 



17 10 



-0-67 



-2-24 



-3-90 



-3-97 



-1-42 



-1-04 



-3-37 



-2-21 



18 10 



-0-70 



-2-50 



-4-68 



-4-70 



-1-77 



-1-23 



-3-96 



-2-60 



19 10 



-0-68 



-3-30 



-4-73 



-4-73 



-200 



-1-34 



-4-25 



-2-80 



20 10 



-0-49 



-3-46 



-4-08 



-3-79 



-1-87 



-M8 



-3-78 



-2-48 



21 10 



-0-22 



-2-50 



-2-38 



-1-69 



-0-76 



-0-49 



-2-19 



-1-34 



22 10 



+ 0-73 



-015 



+ 0-39 



+ 1-16 



+ 1-55 



+ M4 



+ 0-47 



+ 0-80 



23 10 



+ 2-03 



+ 2-89 



+ 3-57 



+ 4-08 



+ 3-73 



+ 2-88 



+ 3-51 



+ 3-20 



10 



+ 2-61 



+ 5-39 



+ 5-37 



+ 5-90 



+ 4-95 



+ 3-78 



+ 5-55 



+ 4-67 



1 10 



+ 2-59 



+ 6-21 



+ 5-77 



+ 6-38 



+ 4-83 



+ 3-71 



+ 6-12 



+ 4-92 



2 10 



+ 1-80 



+ 5-34 



+ 5-16 



+ 5-41 



+ 3-39 



+ 2-60 



+ 5-30 



+ 3-95 



3 10 



+ 0-98 



+ 3-71 



+ 3-89 



+ 3-60 



+ 1-76 



+ 1-37 



+ 3-73 



+ 2-55 



4 10 



+ 0-25 



+ 1-90 



+ 2-23 



+ 204 



+ 0-51 



+ 0-38 



+ 2-06 



+ 1-22 



5 10 



+ 0-07 



+ 0-57 



+ 0-92 



+ 0-88 



-0-14 



-004 



+ 0-79 



+ 0-37 



6 10 



-0-20 



+ 0-07 



+ 0-31 



+ 0-13 



-0-35 



-0-28 



+ 0-17 



-005 



7 10 



-0-47 



-0-23 



+ 0-10 



-003 



-0-86 



-0-67 



-005 



-0-36 



8 10 



-0-78 



-0-79 



-0-08 



-0-25 



-1-28 



-103 



-0-37 



-0-70 



9 10 



-119 



-103 



-Oil 



-0-29 



-1-61 



-1-40 



-0-48 



-0-94 



10 10 



-1-38 



-0-96 



-0-35 



-0-66 



-1-46 



-1-42 



-0-66 



-1-04 



11 10 



-1-15 



-1-26 



-0-62 



-MO 



-1-47 



-1-31 



-0-99 



-M5 



36. The numbers in Table 14 will be found projected in dotted lines, Plate I., where the differences of the 

 results from the whole series, and from the undisturbed series, will be at once apparent. The following are the 

 epochs, in apparent time, of maximum and minimum westerly declination, deduced from the series of Table 14. 



Maximum, 

 Minimum, 



Secondary Maximum, 

 Minimum, 



Dec. Jan. Feb. 

 Ol* 35ni P.M. 

 5h 40m A.M. 

 2h 5™ A.M. 

 IQli 0" P.M. 



JIarch. April. 

 P 5™ P.M. 

 T'^ 40"! A.M. 



May. June. 

 Qh 55m p,M. 

 gh 45m A.M. 



July. Aug. 

 0>» 50ra P.M. 

 &^ 35n» A.M. 



Sept. Oct. Nov. 

 Ql' 30m P.M. 

 1^ 30m A.M. 

 2h Qm A.M. 



9^ 30m P.M. 



37. The principal results from the undisturbed series for the diurnal variation are as follow : — 

 In the quarter, September to November, the minimum of westerly declination is shewn with nearly equal 

 distinctness at night and in the morning ; a well-marked secondary maximum occurring at 2*^ a.m. : a similar 

 result is exhibited in the following quarter ; the morning minimum, however, being less distinctly marked than 

 that in the evening. In both cases we find, in opposition to what has been previously conjectured, that the 

 removal of days of disturbance causes the distinct exhibition of a morning maximum previously masked by dis- 

 turbance. The means for each month from September to February shew the secondary maximum ; it is seen 

 with least distinctness in January. In the couples of months from March till August, no secondary maximum 

 is shewn, the north end of the magnet moves eastwards from about l'^ p.m. till 7^ or ^ a.m., but with less 

 velocity between 5** p.m. and 3"^ a.m., than before the former and after the latter hour. 



mag. and met. obs. 1845 and 1846. 



/ 



