SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1891. 
35 
I’he data given in each case are as follows :— 
(1. ) The number and name of the station. 
(2.) Date of the observations. 
(3.) Initials of the observer and numbers of the instruments. 
(4.) Latitude and longitude of the station. 
For the Declination we give :— 
(1.) The time from the southing of the sun (S) at which the geographical 
meridian was determined by sun observations, a positive sign indicating the 
afternoon. 
(2.) The Greenwich Mean Time (G.M.T.) of the determinations of the magnetic 
meridian. The time is reckoned from the preceding midnight, 
(3.) The observed Declinations with all corrections applied (S), 
(4.) The mean observed Declination reduced to the epoch January 1, 1891 (Sg)- 
For the Inclination we give :— 
(1.) The number of the needle. 
(2.) The G.M.T. at which the observation was made. 
(3.) The observed Dip, with all corrections applied (6). 
(4.) The mean observed Dip reduced to epoch (0„). 
For the Horizontal Force we give :— 
(1.) The G.M.T. at which the deflection (D) and vibration (V) were observed. 
(2.) The corrected independent forces found as described in “Mem.,” 90, p. 73, 
but corrected for diurnal variation and disturbance (H), are given for stations 
at which observations were made in 1889. For subsequent dates only one 
value of the Force is deduced from the observations the value of which is 
equal to the mean of those obtained by the other method (see p. 31 above). 
(3.) The mean observed Horizontal Force reduced to epoch (Hq). 
Longitudes are to be taken as West of Greenwich unless the contrary is expressly 
stated. 
In cases where two stations were very near together the same latitude and longi¬ 
tude were used in the reduction of the observations made at both, and this value is 
given for both in the following Tables. 
The bearings are all from the geographical points of the compass, unless it is stated 
that they are magnetic. 
We think that the data thus given are sufficient for ordinary purposes, but, as 
stated in our previous paper, we intend to place full details of the obseiwations and 
calculations in the hands of the Royal Society, so that, if necessary, they can be 
referred to. 
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