Horizontal Component of Magnetic Force. 



XXXI 



50. The following Tables have been deduced from the 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. 



Month. 



1842. 



1843. 



1844. 



1845. 



1846. 



1847. 



1848. 



1849. 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



•005055 

 •005230 

 •005627 

 •005439 

 •006492 

 •006786 

 •006714 

 •006796 

 •007054 

 •007482 

 •007692 

 •008239 



•008747 

 •008826 

 ■008584 

 •008760 

 •009769 

 •010233 

 •010104 

 •010257 

 •010542 

 •010774 

 •011579 

 •012065 



•012663 

 •012845 

 •012661 

 ■012976 

 •013679 

 •014425 

 •014584 

 •014376 

 •014360 

 •014344 

 •014740 

 •015212 



•014943 

 ■015013 

 •014988 

 •014890 

 •015340 

 •015645 

 •015572 

 •015407 

 •015078 

 ■015461 

 ■015851 

 ■015895 



•016211 

 ■016316 

 •016354 

 •016354 

 •016716 

 ■016570 

 •016939 

 •016388 

 •016233 

 •016480 

 •017161 

 •017775 



•017925 

 ■017573 

 •017806 

 ■017731 

 •017751 

 •018455 

 •018146 

 •018016 

 •017857 

 ■016981 

 •017584 

 ■018591 



•017805 

 ■017649 

 •018064 

 •018406 

 •019054 

 ■019316 

 ■019305 

 ■019116 

 •018552 

 •019230 

 ■019029 

 •019010 



•019392 

 •019620 

 •019638 

 ■020070 

 •020833 

 ■021738 

 ■021358 

 ■020921 

 ■020647 

 •020540 

 •020975 

 ■021600 



51. Monthly Mean Values of the Variations of the Horizontal Component. — The horizontal force has in- 

 creased in the greater nvimber of cases from month to month ; in March or April, and in August or September, 

 the mean is generally less than in the immediately preceding 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. 



Year. 



Horizontal 

 Component. 



Secular Increase. 1 



Each 

 Year. 



Mean of 

 4 Years. 



1842 

 1843 

 1844 

 1845 

 1846 

 1847 

 1848 

 1849 



0-006550 

 •010020 

 •013905 

 •015340 

 •016625 

 1 •017868 

 1 ^018711 

 •020611 



■003470 

 ■003885 

 ■001435 

 •001285 

 •001243 

 ■000843 

 •001900 



•002519 

 •001962 

 •001202 

 •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, than 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 sti'etching 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 

 unaft'ccted 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. 



h 



