Vertical Component of Magnetic Force. 



241 



tember till December. The diminution from January till December is 0-001731 ; if we refer to the previous 

 attempt to connect the different series of observations, we find the mean annual diminution from the beginning 

 of March 1843 till the beginning of March 1844 =213 micrometer divisions ; this, together with the rate of 

 this change, will give 210 micrometer divisions (j= 0*001890) for the diminution from January 1843 to January 

 1844. If proportional parts of this be applied to the monthly means above, the secular change will be elimi- 

 nated, and the annual period rendered more distinct. The corrected means are as follow : — 



Jan. Feb. March. April. 



0-01 I 6924 6899 6690 6555 



This indicates a maximum at mid-winter and at mid-summer, a minimum about April and a minimum in 

 September. It seems, therefore, very probable that the same law holds for the vertical component as has al- 

 ready been shewn to exist for the horizontal component, namely, maxima at the solstices, and minima at the 

 equinoxes. 



From the above the minima at the equinoxes seem to differ little, but the maximum at the winter solstice 

 is considerably greater than that at the summer solstice. 



The range of the annual period is 0-000386, 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



6539 



6771 



6798 



6793 



6599 



6716 



6852 



6925 



TABLE XVI. — 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 1843. 





Variations 





Variations 



After 



Variations 



After 



Variations 



Before 



Variations 



Before 



Variations 



Moon's 



of Ver- 



Moon's 



of Verti- 



Moon 



of Verti- 



Moon 



of Verti- 



and 



of Verti- 



and 



of Verti- 



Age. 



tical Com- 



Age. 



cal Com- 



farthest 



cal Com- 



farthest 



cal Com- 



after 



cal Com- 



after 



cal Com- 





ponent. 





ponent. 



North. 



ponent. 



North. 



ponent. 



Perigee. 



ponent. 



Apogee. 



ponent. 



Day. 



0-000 



Day. 



O'OOO 



Day. 



0-000 



Day. 



0-000 



Day. 



0-000 



Day. 



0-000 



15 



055 







025 







136 



14 



077 



7 



118 



7 



078 



16 



056 



1 



017 



1 



094 



15 



063 



6 



108 



6 



054 



17 



081 



2 



050 



2 



151 



16 



046 



5 



191 



5 



067 



18 



057 



3 



076 



3 



096 



17 



013 



4 



101 



4 



067 



19 



048 



4 



035 



4 



091 



18 



035 



3 



071 



3 



041 



20 



077 



5 



024 



5 



060 



19 



013 



2 



078 



2 



043 



21 



076 



6 



147 



6 



062 



20 



020 



1 



107 



1 



053 



22 



058 



7 



045 



7 



069 



21 



016 



P 



073 



A 



055 



23 



076 



8 



068 



8 



067 



22 



012 



1 



071 



1 



000 



24 



057 



9 



057 



9 



047 



23 



030 



2 



105 



2 



046 



25 



090 



10 



049 



10 



040 



24 



000 



3 



105 



3 



064 



26 



071 



11 



062 



11 



031 



25 



062 



4 



091 



4 



114 



27 



028 



12 



000 



12 



055 



26 



045 



5 



090 



5 



114 



28 



144 



13 



009 



13 



090 



27 



090 



6 



046 



6 



129 



29 



051 



. 14 



on 











7 



064 



7 



110 



Table XVI. was formed from Table XV. in the manner already indicated. Table II. for the declination. 



Variations of the Vertical Component of Magnetic Force with reference to the relative 

 Positions of the Sun, Moon, and Earth, as indicated by the Moon's Age. 



The means shew, with considerable irregularities, maxima near the quadratures, and minima near the 

 syzigies. The principal minimum occurs at the period of full moon, the following means of groups give the 

 same result : — 



14 days to 16 days. Full Moon, 0-000041 



17 20 ... 0-000066 



21 24 ... 0-000067 



25 28 ... 0-000083 



29 days to 1 day, New Moon, 0-000031 



~ 2 5 ... 0-000046 



6 9 ... 0-000079 



10 13 ... 0-00003. 



G. AND MET. OBS. 1843. 



3p 



