324 
STAFF CAPTAIN F. J. EVANS ON THE 
As the recent observations available for this purpose were made between the years 
1866 and 1870, it was not desirable, on account of the large interval between those years 
and the Epoch adopted throughout (1872), to employ the results for that Epoch ; each 
observation has therefore been corrected by an amount which would reduce the decli- 
nation to a mean value for the month of the date actually observed ; this correction has 
been obtained from the Greenwich Observatory Magnetical Tables for 1868, pages iv & v, 
by taking the differences between the mean Westerly declination in each month as deduced 
from the mean of the mean Hourly declination (Table HI.), from the mean Monthly 
determination of the Westerly declination at every hour of the day, Greenwich mean 
solar time (Table II.)*. 
* For the British Islands, with the present average amount of Annual change (eight to ten minutes), these 
will he found useful Tables to obtain the mean value of the magnetic declination for the month when observed 
at any hour of the day. 
The following Table, which is deduced from Tables II. and III. alluded to in the text, has been constructed 
as it presents at sight the required correction, i. e. the amount in minutes of arc to be applied to the Westerly 
declination as observed within the limits of the British Islands at any hour of the day, Greenwich mean solar 
time, in order to obtain the mean value of the Westerly decimation for the month. + sign denotes the amount 
in excess above the mean monthly value, and must be subtracted from the observed declination"; — sign the 
amount in defect, and therefore to be added to the observed declination. 
Green- 
wich 
mean 
solar 
time. 
Jan. 
Feb. 
March. 
-April. 
May. 
J une. 
July. 
August. 
Sept. 
I 
Oct. 
Nov. 
Dec. 
1 n 
. Green- 
I wich 
mean 
1 solar 
time. 
h 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
' 
' 
' 
/ 
h 
0 
+ 2-0 
+ 2-8 
+ 4-6 
+ 5-9 
+ 5*0 
+ 4-4 
+ 4-6 
+ 6-2 
+ 6-8 
+ 5-4 
+ 3-6 
+ 3-1 
0 
1 
+ 2-8 
+ 3-8 
+ 6-4 
+ 8-0 
+ 6-0 
+ 5-5 
+ 6-1 
+ 7-5 
+ 6-6 
+ 5*9 
+ 4-1 
+ 3-5 
1 
2 
+ 2-4 
+ 4-1 
+ 6-3 
+ 7-8 
+ 5-4 
+ 5-9 
+ 6-5 
+ 7-0 
+ 5-9 
+ 5-1 
+ 3-2 
+ 3-4 
2 
3 
+ 1-6 
+ 3-4 
+ 4-9 
+ 5-5 
+ 4-4 
+ 5-1 
+ 5-9 
+ 5-5 
+ 3-7 
+ 4-0 
+ 2-1 
+ 2-8 
3 
4 
+ 0-8 
+ 2-0 
+ 3-2 
+ 3-5 
+ 2*9 
+ 4-4 
+ 4-8 
+ 2-8 
+ 2*2 
+ 2-0 
+ 1*3 
+ 2-3 
4 
5 
+ 0-6 
+ 0-6 
+ 0-6 
+ 1-7 
+ 1-8 
+ 3-1 
+ 3-1 
+ 1-3 
0-0 
+ 0-6 
+ 0-7 
+ P3 
5 
. 6 
+ 0-5 
+ 0-1 
— 0-1 
+ 0-5 
+ 0-7 
+ 1-9 
+ 1-5 
+ 0-3 
-0*8 
-0-2 
+ 0-1 
+ 0-3 
6 
7 
-0-1 
- 0-3 
-0-6 
-0-3 
-0-1 
+ 0-3 
+ 0-2 
-0-3 
— 1-0 
+ 0-1 
-0-4 
-0-2 
7 
8 
— 0-5 
-0-6 
- 1-4 
-0-6 
-0 7 
-0*6 
-0-3 
-0-9 
— 2*4 
-1-7 
-0-9 
- 1-5 
8 
9 
-1*9 
-2-3 
— 2-1 
-M 
— 1-0 
— 0-2 
-M 
-1-2 
— 2* 1 
-2-3 
-2-2 
-2-2 
9 
10 
-2-9 
-2-9 
— 1*5 
-1-7 
— 1-1 
-0-8 
-1-4 
— 2-4 
-2-3 
-2-5 
-2*8 
O.4 
10 
11 
0*4 
-3-3 
— 1-4 
— 1-9 
— 2-0 
— 1-4 
-1-4 
-2*5 
-2-4 
-2-4 
2*4 
-2-2 
11 
12 
-2-0 
-3-1 
— 1-3 
—2-6 
-1-9 
— 1*8 
-1*6 
-2-1 
-2-2 
— 2-6 
-1*9 
-2*1 
12 
13 
— M 
-1-9 
-1*6 
-2-9 
-1*9 
-1*4 
-2-3 
-1*9 
-2-2 
*— 2*2 
-1*6 
— 1-9 
13 
14 
-0-7 
— 1-4 
-2-0 
-3-2 
-2*3 
—2-1 
-2-9 
-1-4 
-1-8 
-1-9 
-1-3 
-1*4 
14 
15 
— 0-2 
— 1-2 
-3-1 
-3-1 
-2*4 
-2-1 
-2-7 
-2-2 
-1*7 
-M 
— 1-0 
-1-2 
15 
16 
-0-5 
-0-9 
— 2-3 

-2-7 
-3-0 
-3*4 
-2-5 
-1*8 
-1-5 
-0-4 
-M 
16 
37 
+ 0-1 
-0-2 
-1*7 
-2-0 
-2-6 
-3-7 
-4-0 
-3*3 
-2-1 
-1-0 
-0-8 
— 1*2 
17 
18 
+ 0-1 
+ 0-3 
-1-4 
-2-7 
-3-1 
-3-9 
-4-2 
-3-9 
— 1-8 
-0*9 
-0-9 
-0-7 
18 
19 
0-0 
+ 0-2 
- 1-5 
-3-8 
-3-2 
— 4*1 
-3-8 
4*2 
-2-0 
-1-5 
-0-6 
-0-4 
19 
20 
— 0-1 
-0-9 
-2-7 
-4-4 
— 33 
-3-9 
-3-4 
-3-4 
— 2-0 
-2-2 
-0-9 
— 0'4 
20 
21 
-0-4 
— 1-0 
-2-7 
-3*1 
-1*9 
-3-0 
— 2*4 
— 2’0 
-1*0 
— 2-0 
-0-5 
-0-4 
21 
22 
+ 0*5 
+ 0-5 
-o-7 
-0-4 
+ 0*1 
— 0-4 
-0-6 
+ 0-5 
+ 1*1 
+ 0-2 
+ 0-7 
+ 0-3 
22 
23 
+ 1-4 
+ 2-0 
+ 2*2 
+ 3-0 
+ 2-8 
+ 2-4 
+ P6 
+ 3-4 
+ 4-0 
+ 3-1 
+ 2-8 
+ 1-7 
23 
0 
+ 2-0 
+ 2-8 
+ 4-6 
+ 5-9 
+ 5-0 
+ 4-4 
+ 4-6 
+ 6-2 
+ 6-8 
+ 5-4 | 
+ 3-6 
+ 3-1 
0 
