144 ROCHESTER ACADEMY OF SCIENCE. [Jan. 26, 
Still another form of induction from these coronal discs is due to 
the orbital motion of the earth in reference to them. In this case also 
a wandering pole is developed, but unlike that just described it under- 
goes very large changes of latitude as well as longitude. Its effect is 
apparent in smooth and sweeping deviations of the needle, which recur 
daily and are entirely different from the fitful and irregular movements 
characteristic of magnetic storms. These deviations depend for the 
most part upon the persistence of the permanent and sub-permanent 
magnetism of the coronal matter, rather than upon sudden variations in 
the extent of its magnetization. They consist of a large deflection 
eastward during the morning hours and a corresponding westward 
deflection about noon, and similar movements eastward and westward 
but upon a very much smaller scale during the night. In Winter this 
diurnal variation is very much less than in Summer, and the time of its 
occurrence is slightly modified. This appears to depend upon a trans- 
ference of the wandering pole, which has been developed, from the 
Winter to the Summer hemisphere of the earth because of some relation 
which this latter hemisphere sustains to the direction of the orbital 
motion. In other words, the earth’s axis remaining parallel to itself, 
and at acertain angle with the plane of its orbit, induction due to orbital 
motion will have its chief effect first in one hemisphere, and then in 
the other, according to the situation of the earth in its annual course 
about the sun. The revolution of the earth on its axis brings all points 
on its surface more or less directly under the influence of this pole, at 
certain hours of local time, the proximity and consequent effect being 
greater in Summer than in Winter. There is, therefore, in this case, a 
compounding of diurnal and annual periodicity. Also in years when 
sunspots and auroras are numerous the range of this regular diurnal 
movement increases, probably because of the increase of the sub-per- 
manent magnetism of the coronal particles. 
There is evidence also that other members of the solar system 
beside the earth are affected by magnetic induction of solar origin. 
There are regular variations of the needle which depend upon the 
position of the moon. The tables of auroras show likewise that mag- 
netic phenomena acquire greater intensity when the moon is in certain 
parts of its orbit. This was noticed moreover by Sir John Franklin, 
in the case of auroras in the Arctic regions. There is evidence too 
that the planets Jupiter and Saturn, in certain parts of their orbits, 
react upon each other and upon the earth by magnetic induction. 
These are phases of the subject, however, which have not been studied 
as yet, except in an incidental way. 
