Diurnal Vaeiations for the Magnetic Declination. 



XXVll 



Table 18. — Mean Difference of the Observations of Magnetic Declination in 1844 and 1845 from 

 the Monthly Means, at the corresponding Hour in each Year, as deduced from all the Regular 

 Observations. 



Mak. 

 Mean 



Mean Westerly 



difference. 







Mean Easterly Difference. 



Mean Difference. 



Nov. 



Feb. 



May. 



Aug. 





Nov. 



Feb. 



May. 



Aug. 





Nov. 



Feb. 



May. 



Aug. 





Time. 



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. 



12 10 



1-43 



1-77 



1-47 



1-80 



1-62 



2-54 



3-54 



1-80 



2-71 



2-58 



1-83 



2-36 



1-62 



216 



1-99 



13 10 



1-51 



1-84 





33 



1-71 





60 



3 



16 



3 



18 



2-07 



251 



2-70 



2-04 



2-33 





62 



2-03 



2-01 



14 10 



1-33 



1-98 





30 



2-01 





66 



I 



80 



3 



07 



1-77 



2-34 



2-23 



1-53 



2-41 





50 



2-16 



1-90 



15 10 



1-38 



1-53 





51 



204 





60 



1 



98 



2 



25 



1-36 



1-94 



1-85 



1-63 



1-82 





43 



1-99 



1-72 



16 10 



1-35 



1-76 





70 



1-63 





61 



1 



39 





78 



1-36 



1-63 



1-53 



1-37 



1-77 





51 



1-63 



1-57 



17 10 



1-05 



1-36 





91 



2-73 





67 



1 



20 





34 



1-41 



1-49 



1-37 



112 



1-35 





62 



1-93 



1-51 



18 10 



1-81 



1-35 





61 



3-84 





98 







97 





14 



1-25 



1-39 



M9 



1-26 



1-24 





41 



2-04 



1-49 



19 10 



1-53 



1-31 





64 



3-00 





81 







91 





08 



1-21 



1-47 



117 



M4 



118 





39 



1-97 



1-42 



20 10 



1-94 



1-72 





84 



2-90 





09 







98 





14 



1-28 



1-64 



1-26 



1-30 



1-37 





51 



209 



1-57 



21 10 



2-00 



1-68 





76 



2-67 



2 



01 





16 





24 



1-37 



1-59 



1-34 



1-47 



1-43 





54 



1-99 



1-61 



22 10 



1-98 



1-99 





45 



1-93 





82 





15 





06 



1-31 



1-50 



1-25 



1-45 



1-38 





38 



1-69 



1-48 



23 10 



1-80 



1-48 





72 



1-64 





66 





23 





10 



1-51 



1-38 



1-30 



1-46 



1-26 





61 



1-50 



1-46 



10 



2-22 



1-93 





54 



1-59 





73 





39 





24 



1-29 



1-33 



1-32 



1-71 



1-51 





40 



1-45 



1-52 



1 10 



2-16 



1-62 





75 



1-73 





80 





47 





23 



1-39 



1-56 



1-41 



1-75 



1-40 





55 



164 



1-58 



2 10 



2-37 



1-80 





59 



2-12 





95 





34 





36 



1-30 



1-52 



1-38 



1-71 



1-55 





43 



1-77 



1-62 



3 10 



2-04 



2-07 





52 



2-04 





91 





76 





33 



1-37 



1-67 



1-53 



1-89 



1-62 





44 



1-84 



1-70 



4 10 



1-99 



1-73 





31 



1-62 





65 





55 





25 



1-27 



1-36 



1-36 



1-74 



1-45 





29 



1-48 



1-49 



5 10 



1-47 



1-79 





04 



1-38 





43 





71 



2 



07 



0-98 



1-42 



1-53 



1-58 



1-92 





01 



1-40 



1-48 



6 10 



1-98 



1-74 







98 



1-61 





62 



3 



71 



3 



79 



0-88 



2-78 



2-54 



2-58 



2-38 





93 



2-04 



1-98 



7 10 



1-46 



1-60 







95 



1-37 





36 



3 



56 



3 



60 



1-29 



2-42 



2-57 



2-07 



2-21 





09 



1-75 



1-78 



8 10 



1-72 



1-61 







90 



1-84 





53 



4 



60 



3 



52 



1-44 



3-25 



3-06 



2-50 



2-21 





11 



2-35 



204 



9 10 



1-54 



1-87 







80 



1-73 





48 



3 



52 



3 



54 



1-64 



3-84 



3-12 



214 



2-45 





08 



2-38 



2-01 



10 10 



1-64 



1-65 







86 



1-69 





47 



3 



65 



2 



86 



1-37 



3-54 



2-77 



2-26 



2-09 





06 



2-29 



1-92 



11 10 



1-66 



1-72 



1 



05 



1-74 





54 



3 



39 



2-67 



1-81 



3-64 



2-84 



2-23 



2-09 



^^ 



33 



2-35 



200 



43. Diurnal Variation of the Mean Excursions of the Declination Magnet, from the Monthly Mean Positions 

 for each Hour, from the Observations for 1844 and 1845. — In the previous investigations, vee have considered 

 the effect of irregular disturbance on the hourly mean position, the frequency of positive and negative excur- 

 sions, and the sums of the latter referred to the hourly means of selected days ; we have still to consider the 

 mean values of the excursions vrhich may evidently follow different laws from the sums, as the latter may de- 

 pend upon both the number and mean value. Table 18 has been formed in the following manner : Half the 

 sums of the differences of the hourly observations from the monthly means for the corresponding hours being 

 positive and half negative, half the sums were divided by the number of positive excursions to obtain the first 

 portion of Table 18, and by the number of negative excursions to obtain the second portion ; the third portion 

 is obtained by dividing the whole sums by the whole number of observations. Table 19 has been formed simi- 

 larly, excepting that the sums of the positive and negative disturbances are unequal (See Makerstoun Observa- 

 tions for 1844, p. 350). The quantities in Table 18 have been termed mean differences, those in Table 19, 

 mean disturbances ; the former being related to the means for all the observations, the latter to the means of 

 the undisturbed days. The epochs of maximum and minimum are nearly the same for both Tables ; those from 

 Table 19 only are given, as it is the best exponent of the laws with reference to approximate normal mean 

 positions. 



Mean Westerly Disturbance. Mean Easterly Disturbance. 



Mean Disturbance. 



Max. 



Nov., Dec, Jan., 1^ p.m. 



Feb., Mar., April, 2^ p.m. 



May, June, July, 8''-ll*> a.m. 



Aug., Sept., Oct., 8^1" a.m. 



Min. 

 lO'^ P.M. 

 6>'-ll'> P.M. 

 9" P.M. 

 9^1 P.M. 



Max. 



6li-9h P.M. 

 9t P.M. 

 12ih A.M. 

 10^ P.M. 



Min. 

 &" A.M. 

 1^-10^ A.M. 

 8^ A.M. & 6^ P.M. 

 8" A.M. 



Max. 



e^'-ii" P.M. 



9^* P.M.-l'' A.M. 

 12^^ A.M. & llh 

 IQh P.M. 



A.M. 



Min. 

 b^ A.M. 



6^ A.M. 



b^-Kfi' P.M. 



5'' P.M. 



44. The epochs given above can be considered only roughly approximative, since the value of the average 

 ' ' excursion for the hours about the times noted often varies very slowly. The points of most consequence in 

 these results are as follow : — 



MAG. AND MET. OBS, 1845 AND 1846. 



