Pas eee 
and Directive Force of the Magnetic Needle. 31 
n the explanation of the deflection of the needle (at 6 A.M. ) 
in iis interval between the solstices it was implied that each of 
the two systems of currents had the same tendency to deflect the 
needle toward the west at the winter solstice, that it had to de- 
flect it toward the east at the summer solstice ;—that is that the 
tween the equinoxes and either solstice would then be half of 
the whole deflection ; Ane ae the deflection from the equinoxes _ 
to the summer solstice s 3/47, and from the equinoxes to the 
winter solstice 1:43. Both sets of currents are concerned i in pro- 
ucing this inequality. As for the morning radial currents they 
proceed from all the points of the photosphere which are exposed 
to the sun, but the character of the result may be ascertained by 
considering the more effective currents. These proceed, at the 
summer sclien, from the points which lie to the north of the 
prime vertical ; and at the winter solstice from the points that lie 
to the south of the prime vertical. The former system of points 
are nearer to the zenith than the latter, and hence the deflection, 
so far as it depends on the radial currents, should be greater at 
the summer than at the winter solstice. It will be seen on refer- 
ring to the Table on p. 29 that the effect of the ecliptic sabes 
is also greater at ‘the summer than at the winter solstice. 
~ values of E at these two periods are about in the ratio of 4 to i 
The inequality in these two values seems to imply that the excess 
f the morning currents of the northern hemisphere over those 
of the southern hemisphere, at the summer solstice, is greater 
than the excess of the morning currents of the southern hemis- 
phere over those of the northern at the winter solstice. In ac- 
cordance with this conclusion we have the fact already alluded 
to that the individual currents of the northern hemisphere . at 
Jeast a portion of them) have a much higher intensity in the 
ter than-in the sammer. But it remains to be ascertained, a 
pore - the variations of declination observed at some sta- 
tion the southern hemisphere, whether the currents of the | 
soutbera savaihore do not experience a coceauontiah diminu- 
tion at the southern solstice. 
HORIZONTAL FORCE. 
Diurnal Va riations.—T he curve of ‘the diurnal variations of 
ima occur about 4 4. m. an p. m., and the minima about 10 
A 10 p.m. It may be conceived, for the sake of more 
ready comprehension, as representing a flood and ebb tide in the 
ethereal sea of magnetic fo orce Maca fall flood tide lagging be- 
hind the sun about 4 hours, at noon and midnight, and the ebb 
