GO 
MR. A. W. RtCKER AND DR. T. E. THORPE ON A MAGNETIC 
Azimuth of Kew Meridian Mark from Sun Observations. 
Date. 
Instrument. 
Observer. 
Azimuth. 
April 22, 1886 .... 
60 
R 
O 
2 
48-4 
Oct. ] 1, 1887 .... 
61 
T 
2 
49-9 
„ 12, „ .... 
60 
R 
2 
48-0 
„ 12, „ .... 
2 
50-1 
19 
5, Li/, ,, .... 
>1 
2 
48-2 
Mean. 
2 
48-9 
Value employed at Kew 
2 
48-7 
At Parsonstown the difference between the reading for the fixed mark and the 
meiidian, as calculated from a sun observation, was l''L 
We also thought that it would be desirable to compare the instruments under the 
normal conditions of use in the field. We therefore made three sets of observations 
at Ard Point, Stornoway; at Bunnahabhain, in the Sound of Islay ; and at Stranraer. 
At the first station the results of the individual experiments made with each instru¬ 
ment were in good accord, but, as the declinations differed from each other by an 
amount very much greater than any possible error of experiment, viz., 18', it was 
obvious that the station was afiected by local magnetism. At Bunnahabhain we took 
the precaution to exchange positions ; these observations were made on a patch of 
limestone, and were in agreement. At Stranraer the sky became overcast, and it was 
impossible to move the instruments after the first determination of the geographical 
meridian. The results show that the station was a good one, and we therefore give 
here the declinations obtained at Bunnahabhain and Stranraer. As we shall have to 
refer to them again, we reproduce only tlie data which bear upon the point under 
discussion. At Bunnahabhain the thread of instrument 61 was broken, and had to 
be replaced in the field, which accounts for the fact that the first observation made 
with it is not in very good accord with the others. The Greenwich mean time is 
reckoned throuo:hout from midnio'ht. 
Bunnahabhain.— Aug. 25, 1888. 
G. M. T. 
Station. 
Instrument. 
Observer. 
Declination. 
h. m. 
10 55 
1 
61 
T. 
2°2 44-0 
11 36 
2 
22 46-0 
10 29 
2 
60 
R. 
22 46-0 
12 25 
1 
22 47-3 
14 30 
1 
22 47-9 
15 9 
1 
22 47-3 
