Vertical Component of Magnetic Force. 



375 



not much different from those for the anuual period, as deduced from the observations in 1844 ; and the result 

 might be stated in the manner already done for the horizontal component and magnetic declination. The 

 average difference of the daily means is a maximum when the vertical component is a maximum, and vice 

 versa. In the case of the horizontal component, the average difference was a maximum when the horizontal 

 component was a minimum. 



The following are the averages of the positive and negative differences : — 

 Jan. Feb. March. April. 



+ 0-000 

 -0-000 



068 



128 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



124 



091 



092 



084 



066 



117 



115 



113 



155 



162 



115 



078 



118 



126 



084 



070 



140 109 079 



119 175 107 



The positive departures from the monthly mean are greatest in the months of November, December, 

 February, and August ; they are least in the other months ; the negative departures are greatest in the course 

 of the year. 



TABLE XXXIX. — Mean Variations of the Vertical Component of Magnetic Force, after eliminating 

 the Secular Change, with reference to the Moon's Age, Declination, and distance from the Earth, 

 for 1844. 





Variations 





Variations 



After 



Variations 



After 



Variations 



Before 



Variations 



Before 



Variations 



Moon's 



of Ver- 



Moon's 



of Ver- 



Moon 



of Ver- 



Moon 



of Ver- 



and 



of Ver- 



and 



of Ver- 



Age. 



tical Com- 



Age. 



tical Com- 



farthest 



tical Com- 



farthest 



tical Com- 



after 



tical Com- 



after 



tical Com- 





ponent. 





ponent. 



North. 



ponent. 



North. 



ponent. 



Perigee. 



ponent. 



Apogee. 



ponent. 



Day. 



0-00 



Day. 



0-00 



Day. 



0-00 



Day. 



0-00 



Day. 



0-00 



Day. 



O-oo 



15 



0000 







0132 







0113 



14 



0081 



7 



0121 



7 



0064 



16 



0038 



1 



0086 



1 



0074 



15 



0035 



6 



0093 



6 



0101 



17 



0082 



2 



0092 



2 



0071 



16 



0045 



5 



0000 



5 



0060 



18 



0078 



3 



0086 



3 



0076 



17 



0093 



4 



0065 



4 



0049 



19 



0038 



4 



0080 



4 



0034 



18 



0065 



3 



0062 



3 



0051 



20 



0126 



5 



0113 



5 



0000 



19 



0027 



2 



0059 



2 



0093 



21 



0113 



6 



0102 



6 



0035 



20 



0074 



1 



0052 



1 



0058 



22 



0103 



7 



0124 



7 



0063 



21 



0022 



P 



0045 



A 



0070 



23 



0146 



8 



0110 



8 



0050 



22 



0018 



1 



0052 



1 



0114 



24 



0148 



9 



0119 



9 



0061 



23 



0088 



2 



0077 



2 



0133 



25 



0126 



10 



0030 



10 



0013 



24 



0004 



3 



0057 



3 



0085 



26 



0115 



11 



0074 



11 



0027 



25 



0063 



4 



0063 



4 



0092 



27 



0104 



12 



0033 



12 



0007 



26 



0057 



5 



0156 



5 



0102 



28 



0046 



13 



0039 



13 



0078 



27 ' 



0087 



6 



0091 



6 



0109 



29 



0075 



14 



0026 











7 



0078 



7 



0086 



This Table has been formed in the same manner as Table II., the rate of secular change employed being 

 0001915 per annum, or = 0-0000052 per diem. 



Variations of the Vertical Component with reference to the Moon's Age. — The means for this component 

 present more irregularities than those for the horizontal component. The following are the means of groups : — 



14 days to 16 days, Full Moon, 0-000021 29 days to 1 day, New Moon, 0-000091 



17 20 ... 0-000081 2 5 days, 0-000093 



21 24 ... 0-000127 6 9 ... 0-000114 



25 28 ... 0-000098 10 13 ... 0-000041 



The vertical component is a minimum at opposition, it is a maximum near the quadratures, and a second- 

 ary minimum at conjunction. 



Variations of the Vertical Component with reference to the Moon's Declination.— -The following are the 

 . means of groups of the second portion of Table XXXIX. 



27 days to 1 day, Moon farthest North, 0-000091 



2 5 days, 0-000045 



6 8 ... 0-000049 



9 12 ... 0-000027 



13 days to 15 days, Moon farthest South, 0-000065 



16 19 ... 0-000057 



20 22 ... 0-000038 



23 26 ... 0-000053 



From these means the vertical component is a maximum when the moon has its greatest north declina- 

 tion ; it is a secondary maximum when the moon is farthest south, and a minimum between these epochs. 



