210 W. A. Norton on the Variations of the Declination 
into acccount the law of variation of their angles of inclination, 
to the meridian, just established, but as I have only seen a meagre 
statement of his researches (in the Comptes Rendus) it would be 
premature to enter into a detailed discussion of them in the pres- 
ent paper. 
It remains to discuss the peculiar variations of declination that 
occur at intertropical stations, whic een signalized by Col. 
Sabine. In the first volume of the Hobarton Observations we find 
the following statement; “the cee variation between the 
hours 2 a.m. and 10 a.m, at St. Helena correspond in respect to 
the direction in which the magnet moves in the months from 
April to August with the phenomena of the Northern Hemisphere, 
and from October to February with those of the Southern Hemi- 
sphere.” Similar phenomena are observed at the Cape of Good 
Hope he comparison between the diurnal movements at short 
idtervals before and after the equinox is-:made in Fig. 7, p. 202; 
the same opposition of movement in the forenoon is here seen 
to exist very near the equinox. These curious phenomena may 
readily be referred to the action of the ecliptic and radial currents. 
hen the sun is north of the equator the currents in the Northern 
Hemisphere predominate, and when he is south of the equator 
those in the Southern Hemisphere predominate. Now we have 
already seen (p. 202) that when the sun is considerably north of 
the equator the tendency of the action of the currents of the North- 
ern Hemisphere, is to impel the needle eastward previous to 6 or 
7 a.m. and afterwards toward the west, and that when he is south 
of the equator the tendency of the action of the currents of the 
Southern Hemisphere is the reverse at the same hours; aud such 
are the actual diversities of movement that have been observed. 
The curves representing them for the months near the solstices, 
as observed at St. Helena, have the same form, and have the 
principal turning points at the same hours as those of Fig. 7. As 
the station (St. Helena) i is in the Southern Hemisphere, the cur- 
rents of the Southern Hemisphere, when they predominate have 
a more energetic action than those of the Northern ere ere, 
when in most effective action. Toward noon, (when the sun 
sses to the north of the zenith,) the radial currents from within 
the tropics will increase the tendency toward the east. In case the 
sun is north of the equator, the radial currents in question and the 
predominating currents from the high latitudes are opposed to each 
other, at that hour, but when he is ; south of the equator they con- 
= Oi to produce an eastward movement. e see therefore that 
the deflection toward the west, late in the forenoon, in the former 
position of the sun should be less than the deflection toward the 
east in the latter position. In the afternoon the radial currents 
that come from points within the tropics will again be in oppo- 
sition to the predominating extratropical currents when the sun 
a 
