384 
ME. C. CHAMBEES ON THE SOLAE VAEIATIONS OF 
show itself, as is the case at Bombay. The proportion, however, of the maximum to the 
minimum range at Greenwich is about 2, whilst at Bombay it is only about T5. 
The variation in the range of the mean diurnal variation of declination is also indi- 
cated by the corresponding variation in the magnitude of the maximum deflections for 
the half years April to September, for each of the first three pairs of terms of the series 
( y ) as delineated on Plate XXIX. figs. 34 to 36 ; but there is also in these figures a curious 
likeness, though not equivalent as to time, in the arrangement of the points for the 
successive years about the centre of coordinates indicative of systematic change from 
year to year in the law as well as in the extent of variation. 
17. Annual Variation and Secular Change . — The observationshaving been repeatedly 
interrupted in the year 1861, it is better perhaps to reject that year and use only the 
two continuous series of observations, 1859 and 1860, and 1862 to 1855, in the deduction 
of secular and annual variations. The following Tables will, however, be filled up for 
that year, although no use is made of the numbers in the calculations applied. 
Table XX. — Showing the mean monthly and annual values of Easterly Declination as 
deduced from the readings of Grubb’s Declinometer in the several years 1859 to 
1865. 
Years. 
Janu- 
ary. 
Febru- 
ary. 
March. 
April. 
May. 
June. 
July. 
August. 
Sep- 
tember. 
Octo- 
ber. 
Novem- 
ber. 
Decem- 
ber. 
Year. 
1859. 
20-592 
20-835 
21-130 
20-868 
21-227 
21-258 
21-366 
21190 
21-569 
22-092 
22375 
22-913 
21-451 
1860. 
23 021 
23037 
23-498 
23-460 
23-562 
24-045 
24-209 
24-506 
24-226 
24-294 
24-932 
25-150 
23-995 
1861. 
25-414 
25 685 
26-158 
26136 
26023 
26100 
25-902 
28-861 
29-041 
29185 
28-632 
28-897 
27-169 
1862. 
29-04 ? 
29-014 
29-178 
29-703 
29-367 
30-416 
30-992 
31049 
31-303 
31-677 
31-820 
32-464 
30-502 
1863. 
32-696 
32 755 
33-948 
34-334 
33 633 
33-424 
33 802 
33-783 
34-407 
34-742 
34-529 
35-471 
33-960 
1864. 
35-262 
35-032 
35-379 
35-331 
35-710 
36016 
36-459 
36-716 
37126 
38-043 
38167 
38198 
36-453 
1865. 
38-568 
38-618 
38-680 
37-816 
39004 
39-499 
40143 
41-251 
41-489 
41-717 
41-241 
42-311 
40028 
Mean of six 1 
years omitting 1 
1861 J 
29-863 
29-882 
30-302 
3-0252 
30-417 
30-776 
31-162 
31-416 
31-687 
32-094 
32-177 
32-751 
The numbers in the last column of Table XX. give values of the annual secular 
increase of easterly declination as follows : — 
From 1859 to 1860 the increase =2*544 
1862 to 1863 „ =3*458 
1863 to 1864 „ =2*493 
1864 to 1865 „ =3*575 
Mean . . . =3*017*. 
This gives a secular increase at the rate of 0'*2515 per month ; and applying corrections 
* It will be seen by a reference to Table III. on page 4 of the Tables of Eesults of the ‘ Bombay Magnetical 
Observations for 1864,’ that the annual secular increase of Declination, •which from 1846 to 1865 had an average 
value of only l'*24, has since the year 1859 been considerably greater, as shown above. 
