MR. A. MA RirCKER ARD DR. T. E. THORPE OX A MAGXETTC 
of the moments obtained at one or two stations immediately preceding and following 
that at which the deflection experiment had been omitted. The total number of 
stations at which vibrations only were observed was 42. 
In tlie case of the Dip observations the correction for diurnal variation was deduced 
from the Kew curves for the diurnal variation of the Horizontal and Vertical Forces, 
which were supplied to us by Mr. Whipple. 
The disturbance corrections were calculated as previously described. 
The following form was used in wmrking up the results :— 
Inclination. Bunnahabhain. Observers: Needle 1, A. W. B. ; 
Needle 2, T. E. T. Dip Circle, Dover, 83. 
Date 1888. 
Xeedle. 
G. M. T. 
Observed. 
V, 
A. 
Corrected. 
h. m. 
0 • 
+ oh 
+ 07 
O / 
Aug. 25 . 
1 i 
12 46 
70 40-2 
70 .39-4 
2 
14 38 
70 39-4 
- 0-4 
70 39-8 
I\Iean. 
(T. 
Reduced. 
70 .39-6 
+ 3-4 
70 43-0 
All the observations were tabulated in these forms, and we propose to deposit 
copies of tliem with the Boyal Society. In this paper we give fewer data. It will, 
however, be more convenient to describe these under the heading “ Results of the 
Observations,” p. 93, and we now proceed to use the tabulated results in a discussion 
of the accuracy of our work. 
Er rors of Experiment. 
The completion of so large a number of observations as those involved in our 
survey, carried out for the most part by two observers with different sets of instru¬ 
ments, affords a good opportunity of testing the accuracy of experiment in the field, 
especially as we have followed a regular practice of determining both the geographical 
and magnetic meridians by means of independent experiments made at an interval of 
several hours. Again, our method of tabulating the results of the Force observations 
furnishes a good test of the various parts of the experiments, and, as will be seen here¬ 
after, we are able, in the case of the Dip observations, to arrive at conclusions as to 
the small errors due to the imperfections even of the excellent needles supplied by 
Mr. Dover. 
