192 W. A. Norton on the Variations of the Declination 
be excited in a similar manner and send off radial, and possibly 
feebler transverse currents. There is however, one possible con- 
ception that might be formed of the nature of the sun’s action, 
which confines the radial currents entirely to the great circles di- 
verging from the point underneath the sun. This is that these 
tions. A longitudinal impulse propagated along the ray proceed- 
ing from the sun, by its obliquity to the surface of the atmos- 
phere would give rise to a current flowing away from the sun, 
But such considerations are foreign to the present inquiry. ‘Taking 
up now the idea of a general electric excitement of the upper at- 
mosphere which receives the sun’s rays, we are to consider the 
various points of the parallel of latitude followed by the sun, (AB, 
Fig. 2,) as acquiring more aud more electric intensity, (that is 
more and more intensity of electric vibration,) as the sun ap- 
proaches them, and as declining in intensity after the sun has 
passed to the west of them. It is not reasonable to suppose, 
however, that the diminution of intensity should begin at the 
moment of the sun’s passage through the zenith of the point, for 
any current excited by the sun’s impulse must decline gradually. 
An hour after this passage, if the sun were to cease to act the 
moment it reached the zenith, a certain portion of the current 
then in existence would still be circulating ; and hence it follows 
that the current flowing from the point in question will continue 
to increase until the diminution of the sun’s impulse overbalances 
the portion of the current that remains undestroyed by the re- 
sistances. The current that follows the meridian of the station 
of the needle (coming from M, Fig. 2,) should then increase 
meridional components are directed toward the south; the east- 
erly motion will therefore continue. During the latter part of 
the night the points that lie to the east of the prime vertical (PA) 
acquire a greater intensity of excitation from hour to hour, but as 
the obliquity of the current that proceeds from the shifting pomt 
of maximum excitement, to the prime vertical, increases, the 
tendency will be to a westerly deflection. This will be dimin- 
i by reason of the greater proximity of the points immedi- 
tely to the east of the prime vertical. In fact, in the summer 
* 
