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LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
available for the comparison. A few remarks however on prominent points may be 
looked for on the present occasion. 
1. The observations of declination, particularly those which point out the course of 
the lines of 0 and of 10° east, indicate a more westerly position than the one assigned 
by M. Gauss in the “Atlas des Erdmagnetismus ” for the spot in which all the lines 
of declination unite. The progression of the lines in the southern hemisphere gene- 
rally, from secular change, is from east to west ; the difference consequently is in the 
direction in which a change should be found in comparing earlier with more recent 
determinations, 
2. The general form of the curves of higher inclination in the southern hemisphere 
is much more analogous to that in the northern, than appears in M. Gauss’s maps. 
For example, the isoclinal line of — 85° instead of being nearly circular, as represented 
in the 3 te Abtheilung of PI. XVI. of the “ Atlas des Erdmagnetismus,” is an elon- 
gated ellipse, much more nearly resembling in form and dimensions the ellipse of 85° 
of inclination in the northern hemisphere in the same work, PI. XVI. 2 te Abtheilung. 
The analogy between the two hemispheres in the characteristic feature of the elliptical 
form of the higher isoclinal lines is the more important to notice, on account of 
the particular relation which appears to subsist in the northern hemisphere, between 
the change in the geographical direction of the greater axis of the ellipse, and the 
secular changes of the inclination generally throughout the hemisphere. The present 
direction of the greater axis in the northern hemisphere is nearly N.N.W. and S.S.E., 
or that of a line passing through the two foci of maximum intensity. In the southern 
hemisphere the present direction of the greater axis differs little from E.S.E. and 
W.N.W. 
3. Captain Ross’s observations of the intensity do not appear to indicate the exist- 
ence anywhere in the southern hemisphere of a higher intensity than would be ex- 
pressed by 2T of the arbitrary scale. In this respect also the analogy between the 
two hemispheres appears to be closer than is shown in M. Gauss’s maps, Atlas, 
PI. XVIII. With respect to the direction of so much of the line of highest intensity 
(2'0) as it has been possible to draw with any degree of confidence from the observa- 
tions now communicated, it will be found to be in almost exact parallelism with the 
isodynamic line of T7 in Plate III. of my memoir “ On the Variations of the Magnetic 
Intensity” in the Reports of the British Association for 1838; which line was the 
highest of which the position could be assigned, for any considerable distance, by 
the aid of the then existing determinations. 
