( Ixv ) 



ADDENDUM. 



117. The process of making and reducing the observations for the absolute hori- 

 zontal intensity made according to the method of Gauss with a 15-inch deflecting 

 bar, has been already described (Introduction, Unijilar Magnetometer), and the ob- 

 servations of deflection and vibration will be found, p. 133-4, 347-8. The results 

 are as follows : — 



Table 12. — Results of the Observations for the Absolute Horizontal Intensity, 

 made with the 15-inch deflecting bar, in 1845 and 1846. 















Mean 





X Reduced 



Date. 



Pairs of Distances. 



Log. — 



Log. m X. 



X. 



of 

 Group. 



Bifilar 

 Reading. 



to mean 



Bifilar 



for 1845. 



1845. 



Feet. 



Feet. 











Sc. div. 





Dec. 29 



5-083 and 9-7083 



0-454510 



1-515975 



3-3942 



) 









5-250 • 



• 9-83 



0-454094 





3-3958 



> 3-3921 



548-9 



3-3869 





5-5 



• 10-25 



0-456497 





3-3864 



1 





• 



Dec. 30 



50 

 5-0 • 



• 6-5 



• 7-0 



0-455291 

 0-455826 



1-513839 



3-3828 

 3-3807 











5-5 • 



• 7-0 



0-455640 





3-3815 



3-3812 



539-1 



3-3807 





5-5 • 



• 7-5 



0-455766 





3-3809 











60 . 



• 7-5 



0-456009 





3-3800 









1846. 



















Feb. 16 



5-0 • 

 5-Q . 



• 6-5 

 . 7-0 



0-455309 

 0-454785 



1-516163 



3-3918 

 3-3938 



■^ 









5-5 . 



. 7-0 



0-454664 





3-3943 



[ 3-3929 



553-2 



3-3866 





5-5 . 



. 7-5 



0-455078 





3-3927 











6-0 . 



. 8-0 



0-455281 





3-3919 









April 14 



5-0 • 



■ 6-5 



0-453826 



1-514334 



3-3904 



) 









5-0 • 



• 6-0 



0-453431 





3-3920 



V 3-3904 



562-3 



3-3800 





5-5 • 



. 6-5 



0-454274 





3-3887 



1 







118. The value of m X, for December 30, is deduced from the 2d series of vibra- 

 tions made upon that day, as there was obviously some error involved in the 1st 

 series ; for a similar reason, the deflection at the distance of 8 feet has not been 

 employed. 



The mean value of X from the previous Table reduced to the mean 



bifilar reading for 1845, = 3-38355 



The mean value of X from the observations for 1844, reduced to the mean 



bifilar reading for 1844, = 3-38005 



Whence the secular change from 1844 to 1845 in parts of X, = 0*00104 



From the readings of the bifilar magnetometer the secular change 1844 



to 1845, = 0-00142 



MAG. AND MET. OBS. 1845 AND 1846. T 



