76 SEVENTH REPORT—1837. 
middle of the larger space, or as 0°9 in the smaller space, 
which has its locality in the Pacific*. 
We may also trace in the intertropical regions another con- 
sequence of the inequality of force of the primary and secondary 
centres. Where the lines of unity approach each other in the 
Pacific, the primary is to the north, the secondary to the south; 
the latitude in which the lines approach is consequently to the 
south of the equator. In the Indian Sea the primary is to the 
south, and the secondary to the north ; and here the latitude 
in which the lines of unity approach each other is to the north 
of the equator. 
Every geographical meridian has a point of minimum inten- 
sity ; if these points in different meridians were connected by a 
line, that line would separate the intensities of the northern 
from those of the southern magnetic hemisphere. It would be 
in some respects analogous to the line of no dip, but it would not 
be aline of equal intensity, as it would consist of intensities va- 
rying from unity to the lowest on the globe. Such a line traced 
on the map is found to differ very considerably in geographical 
position from the line of no dip. 
8. The geographical position of the maximum of intensity 
in the North American quarter is not the same with that of the 
maximum of dip, or with that of the point of convergence of 
the variation lines. 
It will be necessary here to enter into rather more precise 
geographical positions than we have hitherto done. In regard 
to the maximum of dip we cannot err widely in taking the lati- 
tude and longitude where Capt. James Ross observed the dip 
of 89° 59! in 1831, viz. 70° N. and 263° E. That this is also 
very nearly the spot to which the variation lines converge may 
be shown abundantly by the observations made in the different 
polar voyages by sea and land}. It is marked by an asterisk 
* Since the above was written Mr. Erman’s sea observations have been re- 
ceived ; he crossed the space in the Atlantic included by the line of 0-9 some 
degrees to the west of St. Helena, and, midway between the north and south 
portions of that line, found the intensity diminished below 0°8. Captain Fitz 
Roy’s observation at St. Helena is consequently no longer the lowest observed 
on the globe; and it is probable that even a lower intensity than was observed 
by M. Erman would be found a few degrees to the south of St. Helena, and 
nearly in the meridian of that island. 
+ M. Hansteen, who has brought together the observations of dip and va- 
riation made in the different polar voyages, finds that the variations observed 
to the north of the latitude in which the dip is 90° and in the vicinity of that dip, 
converge to a point alittle to the north of thatlatitude ; and conversely, that the 
variations observed to the south converge to a point south of that latitude; or, 
more exactly, that the curves of highest dip are ellipses, having theirgreater axes 
