204 W.A. Norton on the Variations of the Declination 
from any action of radial currents; we. have already seen gone 
the slight effect of these is the reverse at this season. 
course of the forenoon, the ecliptic currents of the natehad 
hemisphere will come into preponderating action ; because after 
6 a. m. the points of meridian passage of these currents will move 
north, toward the zenith of the station, while those of the south- 
ern currenits will decline toward the south. The radial currents 
of the northern hemisphere will also come into action. From 
both of these causes combined, the declination begins to augment 
before the hour of noo 
At the equinoxes the resultant of the entire set of ecliptic currents 
‘would be a single current following the course of the ecliptic trace 
on the photosphere, but for the fact that the currents of the two 
hemispheres cross the meridian under somewhat different angles, 
and in different points (except at the hours of 6 a. m. and 6 Pp. M.). 
At the autumnal equinor, before 6 a. m. the currents of the 
southern hemisphere cross ie meridian to the north of the tropic 
of Cancer, and after 6 a. m. the same is true of the currents of 
the northern hemisphere. aah to 6 a.m. we may represent 
the whole system of currents b a single one in the ecliptic, 
and another crossing the northern tropic, at the point of general 
concentration, in a direction from S.of E. to N. of W. For 
the sake of distinction we will call the former the prima 
and the latter the secondary current. After 6 a. m. the secondary 
current crosses the tropic in a direction from N. of E. to 8. of 
W. Now at the earlier hours the obliquity of the secondary cut- 
rent to the meridian, continually, but slowly, (p. 209,) increases, 
and hence the needle has aslight tendency westward. The primary 
current now crosses the meridian from N, of E. to S. of W., an 
its obliquity rapidly omee and hence an Lowes tendency 
westward. Later than 6 a.m. the secondary current, now in the 
northern hemisphere, aaperianots a slow diminution of obliquity, 
_while the obliquity of the primary current, which now runs from 
.of E. to N. of W., rapidly increases. Both currents therefore 
conspire as before to urge the needle westward. ‘To this west- 
ward tendency in the morning hours is perhaps opposed a slight 
tendency in the opposite direction from the action of the radial 
currents. ‘The facts in the case will be seen on glancing at the 
September column of Table I. The movement is wes 
after 4 or 5a.m., except from 7 to8 a.m. The easterly mo- 
tion at that hour may perhaps be due to the progression north- 
ward of the points of meridian passage of the currents, oe 
with the ae aha of their individual intensities by re 
the westward movement of the circle of excitement. pee in 
‘the forenoon the shifting position of the ecliptic currents, both 
primary and secondary, tends to keep up the increase of declina- 
tion from hour to hour. At noon th heAiiesinncse tinea’ 
Sea 
