226 Proceedings of the Royal Irish Academy. 
in each position as the true position taken up by the magnet. The 
telescope is then directed to the mark on the schoolhouse already men- 
tioned (p. 223), whose true bearing has been carefully determined, and 
the reading taken on the circle. As the suspension fibres are liable 
to be a:ffected by the hygrometric state of the air, and by that means 
torsion introduced into the thread, an experiment is made by putting 
in a known amount of twist, by turning the head of the suspension 
piece, and noting its effect on the scale. The magnet is afterwards 
dismounted, and in its place a plummet of equal weight is suspended, 
which is allowed to take up its position of rest. If any torsion is 
shown, a suitable correction is applied to the reading previously ob- 
tained. 
The values observed in the manner above described are given below 
for the months of March to December, 1888, together with those de- 
termined at Kew Observatory for the same time, the difference between 
them being shown. During the year several periods of disturbance 
have been registered by the self-recording instruments at Kew, notably 
in April, May, August, and October. 
DECLINATION. 
i888. 
Va. 
Kew. 
V.-K. 
March, . . 
22° 35' 
18° 
8' 
+ 4° 27' 
April, . . . 
22 
42 
18 
8 
+ 4 34 
May, . . . 
22 
49 
18 
7 
+ 4 42 
June, . . 
22 
51 
18 
8 
-f 4 43 
July, . . . 
22 
50 
18 
8 
-1-4 42 
August, . , 
22 
53 
18 
7 
+ 4 46 
Septemher, . 
22 
55 
18 
5 
-h4 50 
October, . . 
22 
51 
18 
4 
-1-4 47 
November, . 
22 
52 
18 
3 
-1-4 49 
December, 
22 
49 
18 
1 
-F4 48 
Means, . . 
22 
49 
18 
6 
-f4 43 
