NO. 7.] GENERAL RESULTS. 189 



ARRANGEMENT OF THE RESULTS IN GROUPS. 



As a determination of all three elements was made at only three stations, 

 namely, Nos. 2, 152, and 179, it becomes necessary, if the total magnetic 

 force, or its three orthogonal components, X, Y, Z, are to be calculated, to 

 gather the stations into groups, and calculate the mean of the observation- 

 results belonging to each group. This mode of procedure may be considered 

 quite justifiable when we remember that the position of the Fram often 

 changed only very slightly during long periods, and that the drift of the ice 

 often carried the vessel back again to points in the neighbourhood of which 

 observations had already been taken. By a calculation such as this of the 

 mean values, we also obtain the advantage of being able to reduce to some 

 extent the influence upon the results, of the magnetic disturbances that may 

 be present. The area for each separate group, however, must of course 

 not be made too large, as there would then be a risk of the variation of the 

 magnetic elements with latitude and longitude not standing out with sufficient 

 distinctness. As an experiment, I have taken as the greatest extent for a 

 group, half a degree in latitude, and a number of degrees of longitude to 

 correspond, which makes an area of about 3100 sq. kilometres. The number of 

 degrees of longitude corresponding to a change of half a degree of latitude is 



2-4 in 78 of latitude 



2-6 79 



From the observation-results falling within each of the groups thus 

 defined, I have calculated a mean declination, horizontal intensity, and incli- 

 nation, with corresponding mean geographic coordinates, and thence again 

 a mean value for the total intensity, W, and its three components, X, Y, 



