MAGNETIC DECLINATION AT BOMBAY. 
383 
16. Variation from year to year in the range of the mean diurnal variation of Decli- 
nation. 
Table XVIII. — Showing the range of the mean diurnal variation of Declination for the 
several years 1859 to 1865, and for the component half years (April to September, 
and January to March and October to December). 
Years. 
Range. 
Year. 
Half year, 
April to September. 
Half year, 
October to March. 
1859. 
2-913 
5569 
1-776 
1860. 
3-500 
5-836 
1-763 
1861. 
3-186 
5-365 
1-614 
1862. 
2-887 
4-851 
1-537 
1863. 
2-768 
4-809 
1-435 
1864. 
2-723 
4 612 
1-188 
1865. 
2-590 
4-280 
1-343 
The regular progression in these numbers, the equivalent of which is shown also by 
the varying range of the curves Nos. 23 to 29, Plate XXVII., is very marked, and tends 
towards maxima in 1859-60 and minima in 1864-65, in near correspondence with 
the maxima and minima of the decennial variation of aggregate annual disturbance. 
In order to show the periodicity, the ranges have also been calculated of the mean 
diurnal inequality (including disturbances) for the larger number of years 1848 to 1864 ; 
and the same has been done for the Greenwich observations (excluding certain complete 
disturbed days), with the results subjoined. 
Table XIX. — Showing the range of the mean diurnal inequality of Declination at 
Bombay in the several years 1848 to 1864, and at Greenwich in the several years 
1848 to 1857, with the corresponding ratios of the range of each year to the 
1864. 
2-652 
0-94 
In calculating the average range (2 ,- 808) for Bombay, double value was given to the 
ranges from 1853 to 1859 ; for Greenwich it was taken of such a value (8 ,- 0) as would 
make the sum of the ratios equal to the sum of the ratios at Bombay for the same years. 
Two periods of maximum range are now seen to exist not far from the years of maxi- 
mum disturbance with a minimum intervening, and an approach to a second minimum 
near the last year (1864). The diminishing progression of the ranges for Greenwich 
being (with one slight exception) continuous, shows no signs of periodicity when viewed 
by itself ; but the succession of ratios so much resembles that which appears for the same 
years (1848 to 1857) at Bombay, that it is reasonable to suppose that on the extension 
of the results for Greenwich beyond 1857 an increasing progression would begin to 
average range. 
Years 
1848. 
1849. 
1850. 
1851. 
1852. 
1853. 
1854. 
1855. 
1856. 
1857. 
1858. 
1859. 
1860. 
1861. 
1862. 
1863. 
Bombay .. ■ 
f Range. 
( Ratios. 
3-491 
1-24 
3-248 
116 
3294 
1*17 
2 965 
1-06 
2-611 
0-93 
2-728 
0-97 
2-4 6 
0-86 
2-576 
0-92 
2-453 
0-87 
2-459 
0-88 
2-720 
0-97 
3-117 
1-11 
3-551 
1-26 
3-282 
117 
2-790 
099 
2-568 
091 
Greenwich 
f Range. 
[ Ratios. 
11-4 
1-42 
10-3 
1-29 
10-0 
1-25 
8-4 
1-05 
8-0 
1-00 
6-9 
0-86 
7-2 
0-90 
70 
0-87 
5-9 
0-74 
5-6 
0-70 
