Veetical Component of Magnetic Foece. 



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. May. June. July. Aug. Sept. Oct. Nov. Dec. 



+ 0000 068 140 109 079 124 091 092 084 066 117 115 113 

 -0000 128 119 175 107 155 162 115 078 118 126 084 070 

 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. 



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

 0-001915 per annum, or = 0-0000052 per diem. 



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

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



14 days to 16 days. Full Moon, 0-000021 



17 20 ... 0-000081 



21 24 ... 0-000127 



25 28 ... 0-000098 



29 days to 1 day, New Moon, 0-000091 



2 5 days, 0-000093 



6 9 ... 0-000114 



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, 0000091 



5 days, 

 8 

 12 



0-000045 

 0-000049 

 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. 





