INEQUALITIES OE TERRESTRIAL MAGNETISM. 
415 
June . . 
.... 21° 12-2 
July . . 
.... 13-0 
August 
.... 13-3 
September 
.... 13-1 
October 
.... 13-1 
November 
.... 13-6 
December . 
.... 13-5 
From these are obtained the following Excesses of Corrected Westerly Declination for 
each month above the mean of all the months : — 
Annual Inequality of Western Declination. 
In Minutes of Arc. 
In parts of Horizontal Force. 
January . 
. . -6-04 
0-0000 
February 
. . -0-04 
0-0000 
March . 
. . +0-46 
4-0-0001 
April . . 
. . -0-44 
-0-0001 
May . . 
. . -1-14 
-0-0003 
June . . 
. . -0-74 
-0-0002 
July . 
. . +0-06 
0-0000 
August . 
. . +0-36 
4-0-0001 
September 
. . +0-16 
0-0000 
October . 
. . +0-16 
0-0000 
November 
. . +0-66 
4-0-0002 
December 
. . -f-0-46 
4-0-0001 
The monthly values of the Northerly Horizontal Force were treated in the same way, 
the correction applied being based on the supposition that the annual increase, in terms 
of the whole Horizontal Force, is about 0-0017. This number is derived from the fol- 
lowing values of Absolute Measure of Horizontal Force ; of which it is to be remarked 
that the numbers for 1858, 1859, 1860 are obtained from observations with the old 
instrument, corrected for the constant difference between the old and new instrument, 
those for 1861 from both instruments, and those for 1862 and 1863 exclusively with 
the new instrument. The values are : — 
1858 .... 3-789 
1859 .... 3-786 
1860 .... 3-864 
1861 .... 3-812 
1862 .... 3-819 
1863 .... 3-824 
