142 ‘ ROCHESTER ACADEMY OF SCIENCE. [Jan. 26, 
meteoric particles, as would serve as a conducting medium, not only 
from sun to earth, but much farther, as appears from the presence of the 
zodiacal band and gegenschein, shining faintly though it be, in the 
part of the heavens most remote from the sun. The probability that 
these coronal extensions serve as conductors of electrical impulses 
originating in the sun will be strengthened in proportion as it is found 
that the diurnal, annual and other variations of terrestrial magnetism 
are directly related to the varying location of the earth, and of the 
disturbed parts of the sun in reference to these discs. 
In Spring and Fall the earth, as we have seen, is traversing 
one or the other of these coronal extensions, and it is at these 
seasons as a rule that auroras are most brilliant and numerous, the 
earth then being in the very midst of the conducting magnetic material. 
Thus certain interruptions in the recurrences of similar magnetic con- 
ditions, to which reference has been made, may at length be explained. 
‘They are due simply to the varying position of the earth itself in respect 
to the conducting medium. 
There is evidence, also, that it makes a difference as to which hemi- 
sphere a solar disturbance is located upon. In 1888, and for several 
years preceding, there were series of bright auroras at the interval from 
each other of a synodic revolution of the sun, which were confined 
almost entirely to the Spring and early Summer months of each year ; 
these series being interrupted almost completely at other seasons. 
(Seecolumns 4 to ro of plate.) It 1s likely in this case that the originat- 
ing solar disturbance was confined to one hemisphere of the sun, and 
in proper relation to one coronal extension only, so that its full effect 
was experienced by the earth for a limited period recurring annually. 
In another case, likewise extending over several years, the originating 
solar disturbance seems to have been of such extent as to involve 
both coronal discs, the result being greater persistence of magnetic 
phenomena throughout the entire year, but with the customary pro- 
nounced maxima due to the position of the earth in Spring and Fall. 
(See columns 18 to 24 plate.) Thus another series of the interruptions 
and modifications of periodicity to which reference has been made, may 
be accounted for by differences in the position of solar disturbances, 
with respect to the coronal discs, which serve as the conducting medium 
for the conveyance of the impulses which they originate. 
Other effects of the varying position of the earth in reference to 
these coronal extensions and other effects of their varying inductive 
power, remain to be described. Thus the permanent magnetic poles of 
the earth are displaced from the poles of its axis of rotation a distance 
