times of their occurrence.
Yet again, the atmosphere diminishes in density upwards, and this
diminution will affect the transmission of the electric force.

The result of the _annual variation_ that may be expected from the
magnetic constitution and condition of the atmosphere seems to me to be
of the following kind.

Since the axis of the earth's rotation is inclined 23 deg. 28' to the plane
of the ecliptic, the two hemispheres will become alternately warmer and
cooler than each other. The air of the cooled hemisphere will conduct
magnetic influence more freely than if in the mean state, and the lines
of force passing through it will increase in amount, whilst in the other
hemisphere the warmed air will conduct with less readiness than before,
and the intensity will diminish. In addition to this effect of
temperature, there ought to be another due to the increase of the
ponderable portion of the air in the cooled hemisphere, consequent on
its contraction and the coincident expansion of the air in the warmer
half, both of which circumstances tend to increase the variation in
power of the two hemispheres from the normal state. Then, as the earth
rolls on its annual journey, that which was at one time the cooler
becomes the warmer hemisphere, and in its turn sinks as far below the
average magnetic intensity as it before had stood above it, while the
other hemisphere changes its magnetic condition from less to more
intense.

_II.--Electro-Chemical Action_

The theory of definite electrolytical or electro-chemical action appears
to me to touch immediately upon the absolute quantity of electricity
belonging to different bodies. As soon as we perceive that chemical
powers are definite for each body, and that the electricity which we can
loosen from each body has definite chemical action which can be
measured, we seem to have found the link which connects the proportion
of that we have evolved to the proportion belonging to the particles in
their natural state.

Now, it is wonderful to observe how small a quantity of a compound body
is decomposed by a certain quantity of electricity. One grain of water,
for instance, acidulated to facilitate conduction, will require an
electric current to be continued for three minutes and three-quarters to
effect its decomposition, and the current must be powerful enough to
keep a platina wire 1/104 inch in thickness red hot in the air during
the whole time, and to produce a very bril