Horizontal Coimponent of Magnetic Force. 
XXXI 
50. The following Tables liave been deduced from tlie observations of the bifilar magnetometer in the same 
manner as the Tables already given for the magnetic declination. The variations are expressed in terms of the 
whole horizontal component, the latter being equal to unity. 
Table 22. — Monthly Means of the Variations of the Horizontal Component of Magnetic Force 
at Makerstoun. 
1 
Month. 
1842. 
1 
1843. 
1844. 
1845. 
1846. 
1847. 
1848. 
1849. 
January 
•005055 
•008747 
•012663 
•014943 
•016211 
■017925 
■017805 
•019392 
February 
■0052.30 
•008826 
•012845 
•015013 
•016316 
•017573 
■017649 
■019620 
March 
•005627 
•008584 
•012661 
■014988 
■016354 
•017806 
■018064 
■019638 
April 
■005439 
•008760 
■012976 
•014890 
•016354 
•017731 
■018406 
■020070 
May 
•006492 
•009769 
•013679 
•015340 
•016716 
•017751 
■019054 
•020833 
June 
■006786 
■010233 
•014425 
•015645 
•016570 
•018455 
•019316 
■021738 
July 
•006714 
•010104 
•014584 
•015572 
•016939 
•018146 
•019305 
■021358 
August 
•006796 
•010257 
•014376 
•015407 
•016388 
•018016 
•019116 
•020921 
September 
•007054 
■010542 
■014360 
■015078 
•016233 
•017857 
•018552 
■020647 
October 
•007482 
•010774 
■014344 
•015461 
•016480 
•016981 
■019230 
•020540 
November 
•007692 
•011579 
•014740 
■015851 
•017161 
•017584 
•019029 
■020975 
December 
•008239 
•012065 
■015212 
•015895 
•017775 
•018591 
•019010 
•021600 
•51. Monthli/ Mean Values of the Variations of the Horizontal Component. — The horizontal force has in- 
creased in the greater number of cases from month to month ; in March or April, and in August or September, 
the mean is generally less than in the immediately pi-eceding months. The means for 1848 and 1849 are consi- 
derably less accurate than those for the preceding years, depending as they do on only two daily observations ; 
and the means for the end of 1846 and for 1847 are much affected by excessive disturbance. 
Table 23. — Yearly Means of the Variations of the Horizontal Component of Magnetic Force, 
with the Secular Change. 
Secular Increase. 
Horizontal 
Year. 
] Component. 
Each 
Mean of 
Year. 
4 Years. 
1842 
0006550 
1843 
•010020 
•003470 
1844 
•013905 
•003885 
1845 
•015340 
•001435 
1846 
•016625 
•001285 
•002519 
1847 
•017868 
•001243 
•001962 
1848 
•018711 
•000843 
•001202 
1849 
•020611 
•001900 
•001318 
52. Table 32 contains the yearly means of the quantities in Table 22, together with the resulting yearly 
values of the secular change. The secular change appears to have been very large in the years 1842 to 1844, 
and considerably smaller and more regular in the years from 1844 to 1847 ; the change from 1847 to 1848 is 
smaller, and that from 1848 to 1849 is greater, tlaan for each of the preceding three years. It is not impro- 
bable that the change from 1842 to 1844 is increased by instrumental causes, such as stretching of the sus- 
pension wires of the magnet, while the variation of the changes in 1847-9 is evidently connected with the great 
disturbances of the year 1847-8. If we take the mean yearly secular change from 1845 till 1849, as probably 
miaffected by instrumental error, we find it = 0-001318, the horizontal component being unity ; or, if we take 
the absolute value of the horizontal component, = 3"388, we find — 
MAG. AND MET. OBS. 1845 AND 1846. ^ 
