horizontal needle when under the influence of magnets. 351 
state of the weather had considerable influence on the nature 
and extent of the changes. On several occasions I certainly 
noticed that a cold cloudy morning, with the wind easterly, 
appeared to be very unfavourable to the increase of the 
easterly deviation, but I would not venture to draw any 
general conclusions from such observations. After having 
made these observations, I still farther diminished the direc- 
tive power of the needle, by bringing the magnets nearer to 
the centre. The needle now made five vibrations in seventy 
seconds, so that the directive force was diminished in the 
ratio of 1 to .034,, or was half what it was in the preceding 
case. 
Table of the Diurnal Deviations of a Magnetic Needle, tv hose 
directive force teas diminished in the ratio of 1 to . 034 , by the 
action of two bar Magnets placed in the line of the Dip : the N. 
end of the Needle pointing North. 
April 
*5 
16 
17 
18 
I 9 
Mean. 
h. 
m. 
0 
/ 
0 
✓ 
O 
/ 
O 
/ 
O 
✓ 
Q 
7 
0 
— 
0 
40 
— 
5 
00 
— 
3 
40 
— 
3 
07 
7 
3 ° 
— 
2 
20 
— 
0 
20 
— 
3 
10 
— 
5 
40 
— 
2 
53 
8 
0 
— 
2 
40 
— 
3 
02 
— 
2 
51 
9 
0 
— 
3 
00 
+ 
1 
44 
— 
1 
10 
— 
3 
00 
+ 
1 
40 
— 
0 
45 
10 
0 
+ 
0 
5 8 
+ 
5 
30 
+ 
2 
10 
+ 
1 
20 
+ 
2 
3 ° 
1 1 
0 
+ 
3 
22 
+ 
5 
5 8 
+ 
4 
5 6 
+ 
4 
45 
Noon. 
+ 
7 
00 
+ 
4 
34 
+ 
6 
20 
+ 
5 
5 8 
1 
0 
+ 
6 
40 
8 
+ 
8 
16 
+ 
7 
28 
1 
3 ° 
+ 
>4 
+ 
4 
20 
+ 
4 
56 
+ 
5 
5 ° 
2 
0 
+ 
5 
44 
+ 
7 
00 
+ 
5 
5 ° 
+ 
6 
1 1 
4 
0 
+ 
4 
40 
+ 
2 
5 ° 
+ 
1 
20 
+ 
1 
54 
+ 
2 
4 1 
6 
0 
+ 
0 
28 
— 
2 
12 
+ 
0 
5 ° 
— 
0 
18 
— 
0 
18 
8 
0 
— 
2 
34 
+ 
1 
44 
+ 
2 
10 
+ 
O 
z 7 
10 
0 

+ 
3 
00 
11 
0 
+ 
2 
06 
+ 
1 
10 
— 
5 
3 ° 
— 
0 
45 
